Defects of blue (Roquefort type) cheese

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R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
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DSFtOTS OP B£XIB C S O T S F W f ® D
C0S1SSS
by
ligb®# lays# Bryant
4 Thesis Submitted t© the Graduate Faculty
■ for the Degree- ©?
Major Subject Dairy Bacteriology
•
*
•
Approved?
fa ©barge' ©r
IfStfo»«»
e S d ^ f ^ a j o r Dep&r
lix&*s£a£&sjmk
a or a r i ^ i t e elxiS.
Iowa State College
1940
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
U M I N u m b e r: D P 1 1 8 3 3
IN F O R M A T IO N T O U S E R S
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R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
s F ^ r /
2
€&
*abm
m
ccktbs*s
m m m m m t m
vsmwmt m
5
6
m m m
m t m m
?
Manufacture of Blue Cheese
**.*..*.**♦
7
Manufacture of Cheddar Cheese * * * « • * • • *
8
Media Used
# ....
.
.
8
Preparation of testate juice agar . . . . ... -8
Preparation of acidified feoaaie juice agar
8
Preparation of Csapek'a «g«r . . . . . . .
8
Preparation of beef infusion agar
Plating Cheese
»»******..*..#
* * * .. 10
* » . ... 10
Preparation of sodium citrate solution *' • 10
Preparation of fat emulsion
.......
Preparation of plates
10
10
0© tormina 11on of pH
11
Determination -of'Moisture and Salt (I&C1) in
Cheese . . . . . . . . . . . • . . . . . . .
11
Preparation of Mold Powder
12
. . . . . . . . . .
EXPHMJfSffAb
. . IS
Soft M g ® Defect of Blue Cheese . . . . . . . .
General observations * .... . . . . .
Experimental * . . . .
Discussion
13
» . . 13
,.
15
. . . . . . . . . 03
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r rep ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
3
Conclusion * * ♦ • * . - * * . . * * • • *
Gas Formation In Blue Chans*
.23
* * ******
* 06
General observations , *■ * * * * * * * * *
Historical •* * * * * * * * * * *
06
* * * *- * 0?
Experimental *
.* * . « . * * * * * *
Discussion * ,
** * * * * • . . . . . . . 32
Goncltaslon * * * * * *
. * *27
■* * * * * * * ♦ * * 3©
I*ek of Meld Growth th Blue Cheese
* * * * * * 37
General observations * * * * * * * * *
* . 37
Experimental . * • * « * * * * * * * * *
* 39
Discussion . . . . . . . . . . . . . . . .
44
Ce&eloslen * * * * , * , .
46
**■■*>**.*
frmi tines# in Blme Cheese * * « « * * * * . ' • * * 47
General observations * * *. *■■*■» . * * . * 47
Historical * * * * . * ♦ * * * . ♦ * * * * * * 48
Experimental . * * * * * * * * * * * * * *
Discussion
.* * * *
* .* •
Gonelm«ion
** * * * * . * *
Black Discoloration of Blue Cheese
■*•* *
48
* * * . 54
*■■*■ * * * * * 54
*'*♦*#*
56
General observations * * * * * * * * * . *
56
Historical . * * * . * * * » * * ' . * . . *
57
Experimental * * *. * * . . .
.* *
Bisemailion
* * * * * * * 62
#*■ * * • * ■* * •
Conclusion * •
Gray Discoloration
.*
* * 58
* * * * . . . . . . . . . . 63
of Blue Cheese * * * * *
* * 64
General observations . . . . . . . . . . .
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
64
4
Historical...........................
65
Experimental
68
Mscmaaioii .*
*
0#ao3.mai©m .
*. * *
mmfiwhkiim m
*.
emGw&xm& m
*
*
*
*.•***
**
.76
«st ?iii®s defects 77
4ci»owm)6iii®fs . . ,
,
XXflRtTOT CXTBD *. . .
.. ♦ * * .* , .. « * *
79
.. ,
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r rep ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
.80
*
».*
...
s
B'fftOBTCfJCai
Sine® tbs ripening of the different cheeses Is
primarily a biological process, variations In the results
are to be expected*
In blue cheese, as In most other types,
seme of the variations are of a -minor- nature and the cheese
-showing the® are still considered -satisfactory*.
In other
cases the variations are of -more importance, the cheese
Involved toeing definitely defective*
The objectionable conditions encountered In blue
cheese vary widely, and soat of them ere difficult to
classify.
However, a number of rather specific defects
have been noted -often enough to make them of considerable
practical importance*
In general, the specific defects of
blue cheese are essentially the same as those encountered
in other cheeses*
to improvement In the general quality of blue cheese
requires a reduction In the number of chess® showing minor
variations from the most desirable qualities and the,;,-*
elimination of the cheese showing definitely objectionable
conditions*
As a basis for this, the causes of the various
defects must be established*
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
§
87ATSMBK7 OF FROKUES
•la the work i m m In reported, an attempt was mad® to
determine the causes of a maib*? of the more serious defects
of M u ® cheese.
The defects Investigated are:
m»
Soft edge defect of M u ® cheese
h.
Gas formation la M u ® cheese
c.
Lack of mold growth, la M u ® cheese
d*
Proitiness in Mu.® cheese
®.
Black discoloration ©f M u ® cheese
f * Gray discolorstint*, of M u ® cheese.
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
7
XSTB0D8
.Manufacture of Blue Ghees®
411 silk used for thm aaiatfaetur® of hia® cheese was
homogenised at 03%.* and m pressure of 2,200 pounds per
square inch*
two per aant of a cheese culture was added to
th© mill. and. the milk ripened to an acidity of 0*19 to 0*20
per cent,
lenaefe was added.at the rat# of 3 ounces per
1,000 pounds of mtlkf it was diluted 'to 20 times its volume
with water before addition to th# satUc*
S8°P.
Th© silk was set at
A setting period of 1 hour was used, after which the
curd was cut with one-half inch knives*
fee curd was
allowed to set for 1 hour- with occasional stirring and then
dipped into striae cheese cloths, where it drained*
After
draining for several minutes the mold powder was added and
the curd hooped*
The cheese were turned for' the first time
15 t© .20 minutes after hooping*
They were turned again
four ©r five times at increasing interval# during several
hours and then drained over night*
The cheese war® dry
salted at th® rat® ©f 5 pounds of salt ClaCl) per- 100 pounds
©f green cheese*
After salting the cheese were punched end
placed la th® curing r©#»*
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
a
Manufacture of Cheddar Cheese
Th® milk used to ask® cheddstr cbsese was adjusted
to 86°F. la a vat.
Two per cent of cheese culture was added
and the milk allowed to ripen to an acidity of 0.16 per cent,
calculated ar lactic acid.
Cheese color was added -at the
rat# of 1 ounce per 1,000 pounds of milk and rennet extract
at the- rate-of 3 ounce® .per 1,000 pound# of milk. . The
rennet was diluted to SO biases Its velum® with water before
being, added, to the milk*
the silk m s set for S3 minutes
and then cut with three-sixteenth inch knives.
The curd was
cooked at 1G2°F* until the acidity in the whey reached 0.16
per cent and the desired flrsmess of the curd was obtained*
After dipping, the cord was cheddared until about 0.5 per
cent acidity in the whey was reached.
Upon completion of
the milling, the card was forked for about IS minutes and
then 2 per cent salt was added.
As soon m
the salt'had
completely dissolved, 'the curd was placed la 5 pound hoops
and pressed over night*. The cheese were dried in .a 50°F.
refrigerator for f days and then paraffined*. They were then
placed la .a 50°f. curing room be ripen*
Media Used
Preparation of tomato Juice agar
Tomato juice agar was made as follows?
For each liter,
400 ail. of tomato juice {obtained by filtering canned
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
tomatoes} was neutralised .t« * pH of 7.0*
f®m gm. of Baeto
peptone, 10 gut* of Baeto peptoslsoi utillt and IS gm. of agar
wore dissolved In -600 ml* of water by boiling, after which
the preparation was mad# up to th# original weight and aided
to th# tomato fate©*
fh© rmtlinra was autoclaved at 15 ponies
pressure for 20
filtered end them, distributed in
tubes or bottles and signin' auteelavsd*
Preparation of acidified tomato lute#' agar
form to juice -agar was adJusbed to a pH of 3*5 by
adding & sterile 10 p®r m m % solution of tartaric acid
last, before'pouring
into pistes.*
Preparation of Czapek1© agarCs*p»k*a agar was amde by dissolving th®' following
ingredients In. 506 ml, of distilled waters
Sodium nitrate
2#® gm*
loao»potassiua phosphate
1*0 gm.
Potassium ©hloride
0*5 gm*
Mag*te*liai sulfate
0*5 gm.
Ferrous sulfate
0*01 gm*
Suerese
30*0' gm.
Agar shreds
20,0 gm.
After making mp to 1 liter,. th# medium was ©utoc laved for $0
minutes at 15 pounds ppw»«ia*»«
It was then filtered, dis­
tributed in tubes or bottles m A again autoclaved.
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
1©
ffrspara.ttm of beef InfuaIon agar
Beef infusion agar was prepared fey th© method outlined
in th© Conalttee Report ©a *fh# Xierofeiologiciil Analysis ©I*
Butter" Ctb
Flatlag ^©#®©'
.fy#.g«yatl©ii of aediaa citrate golmtiog
A. Z par eeat eolation of sodium citrate was prepared
fey d t© © © lyin g a
tilled w a te r*.
2
gp* d f ea&lvat ©itre.t* in
100 n il*
I t was pipetted into test tu b e s in
q u a n titie s * s to p p e re d sad s t e r iliz e d
© f dis­
9
m l*
in the autoclave,
fhe tubes w ere stored in a r e f r ig e r a t o r until used*
•Premratlon of fat ©fflsalslon
Si© fat emulsion m n aad* fey adding 0.*5 g®. of agar
and 3 n&+ of cotton seed oil to- 'ft ml» of water in a screw
cap hot tie*
fhe- material was sterilised in an autoclave
and allowed to cool*
As the agar started to solidify* th©
bottle m » shaken to emlstfy the 1*t*
His emulsion was
stored in a refrigerator' until used.*
Preparation of ©latea
One gm* of chocs# was weighedon a sterile piece of
paper
andtramsfeared to a mortar*
fo this was added 9 nil.
©f m sterile aqnaons aodinst oltrat# solution,*
'Hi® chess#
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
11
m.s ground until a hcmcgsnce&s suipsttsicn mmIfc-ed*
On*
ml* of the enalslfiM ©he#»»■ was used 1» making subsequent
dilutions*
the dilations employed-la the plates were
, , , 1-10,000,000, and
1-10,000, 1-100,000, 1-1 000 000
100,000,000*
Beef infusion agar m
1-
msei I© sake th®' total,
proteolytic and lipolytic bacterial counts|for the pro­
teolytic counts, 1 .si* of sterile skin milk was added to eadi
plate before the agar was poarod ana ror the lipolytic counts,
1 ml, of th© fat oisnlaioa mss added..*
0sapel:*s ® M acidified tomato juice agars were used
la plating for molds,. wiitl# toast© fale© and acidified tomato
Juice Agars m m
used for th# detection of yeasts*
■Bet«r»iaati« of pH
Two gn* of cheese was placed in a mortar and ground
to ® thick paste*
fen ml* ©f boiled and cooled distilled
water was 'added,, and th® alacture ground to a homogeneous
suspension*
Measurements were mad© with a potentiometer,
using a qminhydron® ■electrode -end s&tunatod calomel cell,
.Botersinstion of aolsfcgr* and salt {Hall) In cheese
5t» i&stho&s adopted were those rsccmsn&sd by th®
imbcoMltte® Report «n *B®t«'rsiisati« of Fat, loiaiur®,
-and Salt in Hard
(8),
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
12
^reparation ©f.aold powder
£rl«aa»yer flasks ©©staining '0,8 inch cubes of sterile
whole wheat bread'were inoemlated with & water suspension .of
mold spores*
they were inenbated at 80%.. until the bread
cubes had beeese ©oitjpletely
overgrew with aold.
The
contents of" the- flftak* were then placed ©a cheese cloth and
allowed to dry in a wars re-os#* H a n dry, the bread cubes
were grewnd in a sortar b® a fin® powder*
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
13
wxfmmsm&
Soft M g ® gefeeto of Blue Cheese
A defect in which * portion of the edge of a cheese
becomes soft is ©©eaaionelly noted In bine cheese*
Hu®
high humidity at which blue cheese Bust to®' ripened may
favor the development -of undesirable conditions other tham
those encountered In all ripened cheeses*
Th© soft edge
defect is of practical tBportanoe toeeam#-® the defective
edge anwt to# removed before th®' cheese is mark© ted.
general Observations
'The defect in a soft edge chess# is confined to th®
edge# end immediate vicinity*
It usually -penetrates to a
depth of 0*39 t© 1 inch and say extend-, coupletely around
the cheese*
If th® cheese is mot handled or disturbed. It
appears- normal in shape- and color and Ms. the usual slime
formation on the surface-*
firmness of th® ehees#
is tested by presslog with the thumb or fore finger# the
top# sides and bottom of th® cheese are fir® while the
edges are soft*
there is no gradual softening as the
defective ®dg# is approached- tout rather a sharp dividing
line toetwees the firm cheese and the- soft edge*
The
surface of these soft edges is very- easily slipped off
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
14
•xpoalng soft eb*a«© beneath.
fti# soft cheese has the
color and cons latency of a soil ripened eamembert..
At
first, the soft portion ioos not seea to have any off flavor
or odor, but after'a period of about 1 month it assumes a.
llmburger-lllt© character*
This is confined to the soft
material end appears to h a w little Influence on the flavor
of the normal portion*
Betailed observations on this defect were Halted to
one plant*
The first signs of soft edge' were noted on
cheese which had been ripened from 4 to 6 weeks*
In soia®
of the racks of ripening cheese the defect had only developed
on one or two ©ad cheese*
With others the defect had
developed on the edges of on© side of each of the cheese•
In s o w instances th© defect extended completely around
each cheese, and when this occurred It-was often found that
th© defect was ranch sore pronounced m
one side of th© cheese
than on the other; in son© eases there was evidence of th®
defect on cheese in the adjacent rack*
The defect was mot
present In all the eliees® of a single day's make but fre­
quently occurred in some of them and not In others.
It was
much more prevalent during th©- Spring and Srnsmer than during
th# Fall, and Winter*
Investigation showed that cheese in the curing roc®
near the refrigeration pipes and th© humidifier- had the
greatest tendency to develoj soft edges,
This would Indi­
cate that high humidity 'had some thing -to do with the defect*
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
IS
Other.evidence to support this was the fact that if the
pos it ion of the chess# In the ouriug room was change# *
certain locations seemed to effect a partial recovery.*
Experimental
Sine® the general observations indicated that
excess Its humidity In. certain locations is closely relate#
to the development of th® soft edged^defeat in blue cheese,
attempta were mad® to reproduce th® .defect- under experi­
mental conditions.
trial 1.
Two small, 2.5 powtd chees®, which were normal except
for si a®, were place# in the curing room, one near the
humidIfier and th# other as'far as possible from any source
of free moisture.*
After 1 month of ripening th© cheese
near th# humidifier hat developed a acre luxuriant slime
formation than th# control cheese* 13m to-p, hot to®, sites
a M edge# of both cheese were normally firm*
After 6 weeks
ripening the chess# hear the humidifier had developed soft
edges, whereas the- eo&trol'had not, and after 2 months
ripening the -former cheese had developed an advanced stage
of soft edge*
'Th®' edges of th® cheese hat broken away in
spots■revealing smooth, creamy material having a llmburgerlike odor.
In. comparison the control cheese wee' firm and
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
It
appeared to be ripening normally*
The cheese neap the
humidifier vms moved to a position near the control and
allowed to ripen another month*
This resulted in a general
firming of the outside of the cheese*
cheese were cut and observed.*-
both cheese.
At this time both
The sold growth was good In
Ifeither ehesse had developed more than a
suggestion ©f a roquefort flavor.- the- body of the soft
edge cheese was not as firm as the control., probably
indicating a higher moisture -content*
A distinct division
-was noted between the -soft -edge and the normal cheese*
Th#
-soft edge had penetrated to a depth of about 0*75 of an inch.
Trial 2 .
After salting -and punching 'three normal else cheese, a
part of -each cheese was covered with dry absorbent cotton.
The cheese were.then placed la different part# of the curing
room to ripen*
'the positions chosen for th# cheese repre­
sented the average ripening condition# in the -curing room.
The cheese were- examined at 2 week intervals.
The exposed
portion of -each cheese developed a normal slime formation,
whereas the covered portion was slow In developing slime and
the amount was lees fcb&n average*
fhe absorbent cotton
remained dry for about a month, after which a gradual
moistening took place.
By the time th© cheese had ripened
for 2 months, those portions of th® cheese covered with
absorbent, cotton had developed soft edge*
With all three
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
cheese the soft edges had a tendency to penetrate deeper
than usual*
The defect was not confined entirely to fch® .
edges of the cheese hut had a tendency to spread hack from
th# ©ig® and follow the outline. of th# absorbent cotton*
fh# consistency of th® soft ®dg® material was characteristic
©f the defect* hut it had not developed an off odor• Whan
finally cut th# normal portion# of th® efe#®»®:showed good
mold growth -and flavor development*
frfal 3 .
During the muting of two normal sia® cheese, a 2 inch
euhe froa a .peeled potato was placed in th# curd used for
on® of them in such a .position that it was near th# center
of th® resulting cheese.
After salting and, punching, th# .
cheese containing th® potato (the experimental eh©#®#} was
partly covered with pliofilm All® th# other cheese (the
control cheese) was not*
la th# curing room th® cheese
were placed star a humidifier to ripen,
After a ripening
period of i weeks * the unprotected portion of the experi­
mental ehees# ant the control cheese had developed soft
edge-*
the pliofilm was not removed from the experimental
cheese hut th#' eh###® underneath appeared normal and. was
firm to th# touch,.
After a ripening period of 2,5 months,
th# unprotected portion of th# experimental cheese and th#
control showed the soft edge defeat in an advanced stag®,
‘She defeat .had -spread hack from the edge*, end th# soft
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
IS
material had a llmberg®r-like odor.
The cheese under th®
pliofilm still appeared normal to the sight and touch.
When cut, both cheese had a serual mold growth 'and a good
flavor*
The soft edge defect had penetrated about 1 inch.
A sharp dividing line was noted between the normal cheese
and the defective cheese,
the half of the experimental
cheese'left unprotected appeared the same as the control
cheese while the protected half was normal In all respect®.
Ihen th© cheese containing the 'potato was out, there-
was a cavity in it about th© else of the original piece of
potato.
In. this cavity -a shrunken, brown, dry, mass was
all that remained of th®. .piece of potato.
cheese had dehydrate# it.
Evidently the
Hie results show how readily
the cheese takes mp moisture.
Trial 4 ,
After salting and punching three normal cheese, they
were placed in a cooler to dry*
Three days later 'the cheese
were removed from -the cooler and half of each was paraffined.
The cheese wore then placed near the humidifier in th®'
curing room to ripen*.
At intervals th# cheese were turned
in th® rack so that all parts of the cheese would b#
subjected to th® same general conditions, especially
exposure to free moisture*
After ripening; for 2 months
the usp&reffte®d portion of each, cheese had developed soft
edge while th® paraffined portion was fir® to the touch*
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
19
Two weeks, later th© cheese were cut. The unprotected half
of each cheese showed a penetration of tbs soft edge defect
of 0.25 to
0.75 inch.
Th® aold growth was normal and th#
cheese had developed a good flavor* Th© cut surface of th®
protected portion of each cheese showed that there had
been no softening under th# paraffin.
fheti the paraffin
was rtaiw«4, th# surfaces of the .cheese appeared to he
just th# saws as they *»re tha day they were paraffined,
ffee mold growth in the perteeted parts of the three cheese
varied,
in two of the choose the texture was fairly close
and showed little sold growth* the flavor in this area was
lacking.
In th® third cheese* however* th# texture was
wore open'and no difference in wold growth and flavor could
be detected between the paraffined and th# unparaffined
portions of th# cheese*
Uriel S.
A normal cheese was used bo study the offset of certain
hygroscopic materials with reference to their ability to
produce th® soft edged defect.
After salting and punching*
the cheese was placed on a board in th# center of th® curing
room*
Two aluainu® rings* O.S inch deep and 2 inches in
diameter, were used to keep the hygroscopic materials In
definite areas*
One ring m m filled with calcium chloride
and the other with. sodium chloride.
As these salts took
up moisture and is 'turn were taken up toy the cheese.
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
2 0
additional materials wore placed in th® rings.
It was
necessary to replace the ealetuiB chloride w e t sore ■often
then the sodium chloride, this trial was continued for 2
months and although there wee free moisture in the aluminum
rings seat of the tlae, th# cheese failed to develop soft
spots*
Apparently, th# hardening effect of the salts was
greater than the softening effect of 'the Moisture*
Comparative analyse-® of normal and defective cheese.
five experimental cheese, which Included a repre­
sentative fro® each trial that' had developed th® soft edge
defect, were analysed te compare th#' noiwl cheese with,
the soft edge material*.
The eoaparisom. included moisture
and salt contents, p8 and count# of total, proteolytic
and lipolytic bacteria.
Th© data are presented in fable 1*
Hi® Moisture content ©f a moras&l cheese is known to
vary in different parts*
The general, tendency is for the
water portions to be lowest is moisture.
The analyses
show that in every case there was a. significantly higher
moisture content in th® defective soft edge 'than in norm!
portions of th# same cheese, the difference® varying fro®
8.19 to 16*91 per cent.
The unusual relationship suggest®
that the outer portion of th# cheese had taken up and
retained ecnsid«rabl« moisture. ■
Variation# ia salt content ere noted in comparing
different portions of the.##*# cheese or different cheese
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
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R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
MB
from a lot.*
The variation In a cheese la greatest during
the salting, period,, when the salt' content of th® outer
portion la relatively' high, and the content'tends to become
more uniform as the cheese ages because of the diffusion.
In ths- analyses the norsel cheese ■regularly had a highersalt content, than the soft materiel* the differences ranging
from 0.54 to 1.55 per cent.* 'Si# lover salt content in the
soft tutorial presumably m s the result of the water taken
up by this material*
She data show that th®.' soft edge material regularly
had a hlgh©r pH than the normal cheese, th© difference
ranging froa 0*52 to 1.Jff pH unite*
There was considerable
variation la pH between the different normal cheese and
also between the- different soft edges*
The numbers ©f bacteria la different parts of a cheese
or different' cheese normally vary.
With a decrease in salt
content, an Increase in 'bacteria would be expected and this
is clearly shorn in. the data*
A direct microscopic examin­
ation not only confirmed th# difference In numbers between
the normal and soft chees# but also showed that the- soft
cheese contained a variety of bacteria, whereas- the normal,
cheese contained largely cocci,
the great variety of
organisms In the soft cheese suggested the many morphologic
types commonly found in the alia# of normal cheese.
'The softening of a cheese and the production of an
offensive odor suggest a protein breakdown,
if this were
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
2»
im® to bacteria* the eheeee should show the presence of
significant numbers of proteolytic types*
The bacterial
counts indicate that la no ©«««-. were significant numbers
of proteolytic .or lipolytic bacteria detected la the soft
material*
Figaros 1*. and 2* illustrate the soft edge defeet
In the cheese analysed; fig®*® 2* shows particularly the
depth to which the softening m y penetrate-*
Bisemssioa
The development ©f soft edge la him© cheese appears
to be the result ©f an eeewnletieie of moisture on the
cheese,
the logical piece- for softening to occur would
be the edge, since- her® two surfaces are separated by a
relatively m i l amount -of -cheese and. the ratio of
deposited moisture to eheese is high*
Moisture deposited
on other parts of the cheese would not -have- the same
significance.*
fhe Increase in moisture results In a
decrease In salt content, and 'this in turn may permit
greater activity of organism* or -of their enzymes.
In -a curing room a humidifier aay be responsible for
moisture being deposited directly on the -cheese .near it,
the amount depending on th® manner .of operation and other
factors.
Ordinarily* a humidifier is- essential In a
earing rean but If it Is- properly located and shielded
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
24
Cheese Showing Soft Kdge Defect
Figure 2,
Che©as Showing Deep Penetration of
Soft Mg® Defect
m
Figure !♦
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
ES
there is little Ganges' from it*
The refrigeration coils were else- involved la the
development of th@ defect in earing rooms.
Variations
in the brine often result in frost formation on the eoils.
than the coils warm and defrost, they evaporate moisture,
some of which may he condensed on the cold cheese.
If
moisture drips from the coll* it may fall ©m cheese or
splash on it.
Proper refrigeration readily eliminate#
the danger from the coils.
the reproduction of the soft edge defect by ripening
cheese near a humidifier or refrigeration coils explain#
the defect in artificial -curing rooms.
While the defect
appear to be unusual In caves, it has been noted there..
Presumably,,, conditions in a cave could result In moisture
being deposited on a cheese.
If the air were saturated
with moisture and fresh cheese were brought into the car®,
air currents could carry moisture'' from the fresh cheese
to the older cold ehe©#®*
Conclusion
A defect of blue cheese in which a. portion of the
edges became soft appeared to be caused toy excessive
moisture in the softened part# of the cheese*.
The defect
was readily reproduced toy placing cheese close to a
humidifier where free moisture could strike the cheese.
R e p ro d u c e d w ith p erm is sio n o f th e co p yrig h t o w n e r. F u rth e r re p ro d u ctio n p ro hib ited w ith o u t p erm is sio n .
m
Gas Formation la Blue Cheese
See produc Ing organisms are found In various dairy
products, Including cheese.
In some of the swiss type
cheeses, the characteristic eye formation is due to gas
producing organisms, Including those of the .genus
and is highly desirable.
In other types
of cheese, end particularly In eheddar cheese,' the produc- '
tloa of gas and the associated flavor constitutes a serious
defect,
The most common gas producing organisms causing
defects in cheese are member® of' the gseherlehla-iterotoacter
das formation Is knows to occur In blue cheese but
group,
Is of much less Ispertoaitce than in Cheddar cheese.
General -Observations
Gas formation has been observed In only a few blue
cheese,
The defective cheese were all imported, and while
the volume of domestic cheese is small, no gassy cheese of
this type has been observed,
'St® defective cheese were
not bulged and from the outside appearance did not disclose
the presence of gas holes*
Th® holes varied In size, were
practically round and seuatimoa were present in Moderate
numbers,
The mold growth was normal and the flavor did
not seem, to to® affected.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
liistonicmX
The gassy defect In. «bseat has been studied by
various Investigators bat* in general* they have confined
their observations fe© ©bees® of tbs Cheddar type*
Moore and
Ward (21) reported that a gassy condition in ©bees® curd*
which was aeeosspsiiied by an off ©dor* was due to. an
lseherl.eMa*Ier©baeter organism*
HarshalX {18} noted that
the colon organisms produced ||as boles in cheese alone but
not wt&n « igood starter was atfied*
la lew Zealand*
Whitehead (28} found that. wh«4 colon types were added to
milk* the resulting cheese developed unclean flavors but
no gas holes.,
telteh <1?J reported that the production
of gas la Cheddar cheese curd. mss mostly due to the colon
■group but s-ossetiaes was 'due to Bacillujt a O & U . or certain
yeasts*
Experimental
Although the general observation# indicate that gas
production in blue cheese does not have the same signifi­
cance that It does in Cheddar cheese* several trials war®
carried out, to determine the Importance of gas production,
by the Eaeherlchla-Aerobacter ban terla. la blue cheese,..
Cheddar cheese being used m
a control*
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
23
Trial 1*
A Quantity of fair quality raw silk was obtained
& M divided Into- two equal portions of about 100 pounds
each,
fti® milk for tela© cheese was homogenized, cooled
to 60°F. and placed in a refrigerator.
The milk for cheddar
cheese was divided into two equal portions of approximately
SO pound® each, and each lot was placed in. a compartment of
a five section experimental cheese vat#
two per cent
cheese starter was added to each portion*
One portion was
used a® a'control and to the other was added 10 ml* of a
milk culture of Aerohaeter aerogenes# which, had recently
'been isolated -fro*, gassy eheddar cheese*
manufactured In. the usual » ® » p *
the cheese was
'When it had reached
the eheddar lag stage, the bottegcelsed milk was taken from
the cooler and the mmfsctur# of the blue cheese was
begun,
this procedure was necessary because of the- dif­
ferent temperatures employed la the manufacture of the two
different types of cheese and because all five compartments'
of the vat were heated by the same jacket*
The milk for
the blue cheese was divided into two equal portions of
approximately 50 pounds each and each lot- placed in ©a®
©f the unused compartments of the cheese vat.
'two per
cent cheese starter was added t© each lot of milk*
One
listed in Bergey's Kemtel of Determinative Bacteriology
(2) •
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
29
compartment m s kept as a control and to the other m s
added 10 ml* of the eultotr# of 4 *.
cheddar cheese*
manner,
used with the
fha eh®©#® was ssnufactured in the usual
fh© tolu® cheese curd from each compartment mad©
on®' normal si®# cheese.
The two eh®®#® war® salted,
pinched and placed la the caring row® to ripen*
The cheddar
cheese curd fro* each compartment m s pressed into a loaf
of approxfinitely 5 pounds,
fbm two cheese were dried.,'
paraffined, end placed in a SO^F, experimental cheese cooler
to ripen*
After 1 month of ripening the experimental cheddar
cheese was very slightly bulged and the cut surface showed
large numbers of small gas holes*
fh® flavor and odor were
unclean and suggestive of gassy cheese,
The control Ched­
dar cheese had a normal outside appearance, and while the
cut surface w®® solid for the
most part, it had a small
number of opening® suggestive of gas holes*
and odor, however, were mild and clean*
fh@ flavor
The him® cheese
were examined at this time also hat war® not cut*
The
outsid® appearance of each was normal, and several plugs
draws from each Indicated that the » ® M growth and texture
of both cheese were good, ti© off flavors ©r gas holes toeing
noted*
After' a ripening period of 2 months tooth the cheddar
and the. tola® cheeses were cut*
The observations made at
the end of 1 month of ripening were confirmed.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
so
Trial 2,
A good quality raw silk ws®, -obtained and trial 1
repeated* with the exception that to each experimental lot
of mllk 20 ml. of a silk culture of A* aerogenes was added
instead &£ 10 si*
'The eheee* war® allowed to ripen 2
months before being cut and observed*-
The experimental
eheddar cheese was normal In shape- but the cut surface
chewed large number® of gas holes ami the cheese had an
unclean f laser * The control Cheddar cheese was close
textured, free from any openings suggestive of gas and
had a mild* clean flavor.
The experimental blue cheese
showed a few small gas holes but- the number and sis® war*
.such that they would b© noted only on careful examination;
for the most part the holes were in the outer portion of
the cheese, As is usual, the center of the- chocs® was
more open than the outer portion*
She mold growth In
the cheese was normal and some of th© characteristic flavor
had developed} an unclean flavor was not detected*
control blue chess® was free of gas holes.
The
The mold growth
wet normal and the eheeae had began to develop a desirable
flavor.
Figures 3 and 4 show -the cut surface© of the experi­
mental and control eheddar cheese.
Trial 3.
Milk similar to that used In trial 2 was- pasteurised
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Figure 3.
Caasy Cheddar Cheese lad® From law 111k
Inoeulistod W ith A ero o acter
m
m
Figaro 4* Control Cheddar Cheese lade Without
Inoculating law 111k With Aorohacfcor aerogonea
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
St
at 145%. for 50 minutes , and trial 2 was repeated.
The
cheese were allowed to ripen for 2 months and were then
out and observed*, The experimental Cheddar cheese was not
definitely bulged; however, it was filled with many small
gas hole® and had an unclean, slightly bitter flavor, with
no typical cheddsr cheese flavor,
tbs control Cheddar
cheese was close tsxtured and free of gas holes hut was
slightly hitter and lacked eheddar cheese flavor*. Both
blue cheese appeared normal and showed no gas holes j with
each there was a more compact and brittle body than is
normally found in raw
milk cheese, and although there was
good mold growth the. cheese lacked flavor*
fhe cut surfaces of the experimental and control
Cheddar cheese- are shown in Figures 5 and 6.
Fro® Figures
7 and 8 it Is evident that the cut surfaces Of the experi­
mental and control blue cheese were essentially the same.
m&i£*
Regular pasteurized market aiilk was used to repeat
trial 5* 'The results were essentially the same as those
obtained la trial 3*
Discussion
Ih# natch greater production of gas holes by A* aerogenea
la eheidar -cheese than in blue cheese presumably was due to
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
m
Figaro 5*
Q«®«f Chedder Ghees® lfs&* From Pasteurized.
Mill Inoculated With Aerohacter aerogenea
Figure 6. Control Cheddar Ch*®s® lad® Without
Inoculating Pasteurized Milk With Aarohaetor ^eroaenea
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
34
Pigur# 7. B l m Cheese Mad# frsu Pasteurised Milk
Inoeulatsd Witte Amrotmet&p
S© Gas Evident
Figure 8. Blue Cheese Mad® From Pasteurised Milk
lot Inoculated 'Witte Aerobaeter .aorogenea« No Gas
Evident
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
55
.several factors.
Perhaps the most important was the
difference in texture between the two types of cheese*
In cheddar cheese the texture is close and retards the
escape of gas# while in blue cheese the texture Is open .
and gas should escape readily*
In milk used for blue cheese, homogenisation results
in an early■production of fatty acids which have an
inhibitory effect on various bacteria*
Walls the cheese
culture organisms apparently develop rapidly In the milk,
they are present in relatively large numbers and less
effect would be expected on them than on species present
in much smaller
number® *
The temperature® employed in making blue cheese are
not as high, especially during the cooking process, as
those used in cheddar cheese*
The higher tempera tares
in cheddar cheese would tend to favor the development of
A*
aerorenes *
Presumably, the results obtained with A* aerogenes
are essentially the same as those' that would be obtained
with other species ©f the Egcherieh1a-Ae r obac ter group*
Conclusion
<3** formation is of relatively little importance in
blue cheese, presumably because of the open texture, which
permits the gas to escape * and the unfavorable conditions
Reproduced with permission o f the copyright owner. Further reproduction prohibited without permission.
m
In the cheese for the growth of ■the ea w u m gas forming
organisms* 'trials with a culture of A* aerogenea freshly
Isolated from gassy sheddar cheese shewed that Inoculations
(of the m i l k ) which resulted In w r y gassy cheddar cheese
caused no gas holes or only Insignificant numbers in bln#
eh©###*
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
m
lack of Hold growth in Blue Cheese
A lack of mold growth, oeeesionolly Is noted in blue
cheese.
In certain cases It probably is caused by too
abort a ripening period#
This undoubtedly applies to some
of the foreign- cheese, especially when there is either a
shipping deadline ©r * sharp Increase in demand*
With
further ripening such cheese coBtraonly derelops a normal
mold growth and flavor.
1m other cases the cheese lacks
mold growth even after extended, ripening.
.Often this
defect 1® not discovered "until after the cheese has been
cut, at which time the cause is difficult to determine.
Occasionally, however. Hie defect Is discovered at .such
a time that definite information on it can be obtained*
General Observations
An opportunity to study a» outbreak Involving a
lack of 'sold growth in blue cheese occurred when a commer­
cial cheese plant experienced the defect*
•occurred suddenly*
fh© outbreak
1 high quality cheese was .produced up
to and including the lot manufactured December 24, 1938.
Cheese samfabtmred on end after December fi-, 1938, did
not develop normal mold growth or flavor*
From the dally
plant record* it was noted that the ehe©s©maker had
obtained fro® a laboratory a fresh supply of wild powder
on December -24;, 1938*
This .mold powder was used to make
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
m
cheese the following day and thereafter at the rate of
about three times a week.
The cheese were handled in the
usual manner and, on the basis of slime formation, appeared
to be ripening normallyj the surface developed a good slime,
and some cheese also had considerable mold growth on the
surface*
When the first few lots of cheese made with the
new mold powder were about 2 mouths
for mold growth by plugging
old, they were examined
two or three cheese in each lot*
fh© plugs showed very little acid growth*
However, sine©
the ©ufcsid© appearance of the cheese was satisfactory, the
cheasemaker concluded that the
that it would develop later.*
continued as scheduled*
mold growth was slow and
She manufacture of cheese
About 1 month later another routin©
sold examination showed the cheese lacking In mold growth*
The cheese previously plugged were examined a second time
and the plugs showed no Improvement in mold growth*
A
.systematic investigation of mold development was then begun*
Several cheese in each lot were plugged and at least on©
cheese cut*
formal mold growth was not present In any of
the cheese examined*
Certain of the cut cheese showed
areas of normal mold growth, while other© were perfectly
white. In some case© It appeared that the mold had invaded
the cheese through the- punch hole#*
fro® the observations
the eheesestaker concluded that the lack of mold growth was
due to defective mold powder and discontinued the manu­
facture of blue cheese until -a new supply of powder could
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
§9
be obtained.
Upon receipt of the fresh Mold powder the
manufacture of bine eh*«*« was eontinned..
. .Several lots
were made and kept under observation*
The cheese war®
plugged several’times, beginning'at about S weeks and
ending after 6 weeks of ripening*
The presence of normal
mold was not observed In any of the plugs*
fh® second apparent failure of the mold powder was
called to the attention of the laboratory supplying the
powder*
The laboratory reported that another cheese
plant had used a shipment of' the same mold powder and
had not encountered any difficulty in obtaining normal
mold growth in its oboes#*
A m m supply of mold powder
was sent to replica that which .was questionable*
Cheese
ttsnafactured with this powder developed normal mold growth*
then the defective cheese were from 4 to 6 months
old an effort was muds to salvage some of them*
The firmer
cheese were repaneheti and inoculated with a water suspension
of normal mold spores*
This was successful in that many
cheese later- developed enough flaw®? to be salable*
It was
estimated -that the outbreak, involved some .§,000 pounds of
cheese and feat about 1,000 pound# were eventually marketed*
Skperimentnl
A sample of the questionable mold powder was obtained
from the commercial cheese plant*
The powder was somewhat
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
4 0
light®** in color than aortal*
it w&s plated ©a Csap©k*s
agar and the plates incubated at 22°C.
developed rapidly m
ster11a 'sgroalina*
Mold colonies
this medium and had a vide margin of
ft® sper** vara blue greem In color
and spread from the center to the outside of the colony
with age.
Ibil® the colonic* ©f the mold were not typical
of femiolillum rocmefortl . they ware near enough to he
accepted as on® of the species of Fen lei Ilium mead in
asking the blue veined cheeses.
When the questionable
mold powder was plated ©a acidified tomato. jute® agar
under the same- condition** a very different type- of
colony developed*
The colonies were more compact* slower
growing* white in color and failed to produce m blue green
color- even after weeks ©f gppowtkf. they did not resemble
colonies of the penlclllla e o M o n l y used la bln® veined
cheeses.
Flasks of whole wheat bread were inoculated with
the questionable mold powder and incubated at 10°C.
fh®
resulting mold growth was blue green in color- and appeared
to be identical with that of normal P. rogueforfcl.
Trial 1*
.la attempt was made to reproduce the defect la
experimental cheese by inoculating with the original
questionable sold powder*
A quantity of blue cheese curd,
-sufficient to make three cheese of about- 2.5 pounds each*
was prepared*
This was divided into three portions.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
To
41
on© lot was added norma1 mold powder, to the aecord lot a
mixture of questionable and normal mold powder and to the
third lot ©sly the questionable mold, powder . The curd, was
then handled la the uismal muum?*
After salting and
punching- the -cheese.* the surface. of the cheese containing
only the fusstioiiiibl©- powder was treated with calcium
propionate and the cheese.wrapped in parchment paper to
limit mold contamination from the outside.
The three '
cheese were then placed lit the regular- curing roes*
After
a ripening 'period of 2 months: the cheese were cat and
observed,
The cheese eefttelnlmg the .mixed powder shewed
areas of normal mold growth and other areas in which no .
mold growth could be detected*
Use cheese containing the
questionable powder did not show any mold .growth*
control cheese had a normal mold growth*
The
«hen. the- cheese
had ripened for S months* they were cot and observed a
second time.
The cheese containing the mixed powder did
not show any marked lapreveme&t la sold growth, although
there was s e n Increase*
Flavor development was lacking*
1© mold growth or flavor was noted in the cheese containing
the questionable powder*
The control cheese had about the
same- mold growth as when first examined hut met definitely
lacking in flavor.
Trial 2%
Trial 2 was a repetition of trial 1 with the
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42
exception that tbs- ©bees® were et m m m % » l m and the one
made with the questionable pewter was not treated with
calcium propionate or wrapped ta parchment.
fh© cheese
were ripened 2 months and then oat and observed . The
cheese containing the mixed powder showed a fair but rather
Irregular growth of iiomal » M
appreciable flavor.
bat' had not developed any
U » cheese containing the questionable
powder showed an occasional small area of normal mold
growth*
These areas were near the surface of the cheese
and appeared to have been dm© to an invasion of the- ©he®»©
through the- punch holes *
tee control cheese showed m good
mold growth and had developed ©on© flavor.
H u m the cheese had been ripened for 3 month©* they
were again cut ©ad observed*
fh# ©&©•«© containing the
alxsd powder had improved, somewhat in mold growth and had
developed a fair flavor.
The cheese containing- the ques­
tionable powder appeared about the same as at 2 months;
however., in tb@ small areas of normal mold growth cew©
flavor development had takes, place,
fh© control cheese
had about the s a » sold growth as at 2 months and had
developed a fin© flavor*
Trial 1.
Several samples of the original commercial eh©**©
showing a lack of a d d growth and several samples of
experimental cheese showing the defect were plated la
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45
the usual manner on Csjapekis and acidified tomato juic®
agars.
Characteristic colonies of the questionable 10M
ware noted on plates poured with ©sofa cheese.
Some of
the colonies were picked and purified fay repeated platings.
Feeder A was prepared with a culture obtained from
the eoaaaerelftl cheese by Inoculating. whole wheat bread in
the usual manner*
Powder B was and# with m culture isolated
froa experimental cheese that lacked mold growth.
Sufficient blue cheese curd was prepared to make
three normal sine cheese*
portions*
The card was divided into three
To the first lot normal powder was added, to the
second lot powder I was added and to the third lot powder
B was added*
She cheese were handled, in the usual manner
and after salting m & pinching were placed in the regular
curing room.
After a rlpeaimg period of 2 months, the
cheese were cut and observed*
The two cheese made with
powder A ©r powder B showed very little sold growth and
had no flavor*
The control cheese had a normal
and had developed considerable flavor*
cheese were again cat and observed*
10M
growth
After 5 months the
The cheese made with
powder A and powder B were still lacking in mold growth
and flavor.
The control cheese appeared about the same
as when previously examined*
Xdon fcif1ca11on of mold in defective powder»
A number of mold cultures that had been isolated from
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44
the original defective mold powder or from cheese mad© with
it* as well as culture# fro®, the experimental cheese that
laelsed soli growth, were studied in more or less detail..
Identification studies were carried out with cultures grown
on Csapdk** agar*
Xiereeeopleal observations and measure­
ments suggested that the organism was Penlelllium eehlnafeum.
according to the classificatt-on of Oilman and Abbott (11)*
Cultural characteristics suggested, 'that the. organism m s
f* roqueforti according to llourg# (3}.
'fee cultural
characteristics were accepted rather than the microscopical
observations and the mold is considered 'to be an atypical £*
roqueforti.
Discussion
Several epeeiee of the genus Peniellllum have been
used successfully in the ripening of blue'cheese but other
specie# are not satisfactory*
Although the. organism
present in the defective mold powder was regarded ss an
atypical strain of £* roqueforti* it did not develop well
in blue cheese*
fee culture used to prepare the powder
had been carried on as artificial medium for an extended
period* and this may have resulted in a variations however,
there remains the possibility of the contamination of the
culture wife an organism which outgrew the original type*
Because of the very close relationship between
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45
captain species of the gamut Fentolllluiu it would be
difficult to detect contamination op variation of a cul­
ture used to prepare a © M powder*
In case there was
©ont&slnatlon, or variation the first indication night
be the failure to produce normal mold growth- in cheese.
The questionable mold powder was sent to two
commercial cheese plants*
One plant h«d difficulty in
getting s normal mold .growth with it All© the other did
not.
She plant having difficulty received and used several
pounds'of the powder while the other plant received only
2 pound.
At the plant having no difficulty* the cheese
normally 'had an unusually «ct#»#2v® mold growth, although
the rate of inoculation of powder was the same as in
pleats snaking cheese with less abundant mold growth*
This
Indicates that the c!»@«® mad* in the on® plant was either
receiving &
natural Inoculation of mold while being menu-
•factored and ri pened or that conditions were exceptionally
favorable for' mold growth in the cheese,
fh©-experimental
results support the former assumption; cheese Inoculated
with questionable mold powder*, treated with calcium pro­
pionate and wrapped, in parchment paper failed to show any
growth of sorisal mold, whereat cheese not treated with
calcium propionate or 'wrapped' in parchment showed some
areas of normal mold growth.
It appears that under certain
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m
conditions enough natural inoculation occurs, to produce
fair mold growth and'.flavor la cheese.
la order to avoid slow noli development la the cheese,
the mold powder mast be carefully controlled.
It !»■
advisable to establish the effectiveness of a new lot of
mold powder by using It ia on® or two runs of cheese before
It Is employed la more extensive operation®.
There may be
an advantage In occasionally Isolating a fresh culture of
X* goshftfrftpfcl front » good blue cheese end using it lu the
preparation of powder.
Cc®elusion
The Incite of meld growth in the outbreak studied
apparently wa® caused by the use of a mold powder In which
an atypical strain of f* rooaefgrtl predominated.
Hie
variation in the sold tuny have been caused by the long
continued cultivation on an artificial medium of the cul­
ture used to prepare the powder*
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m
Fruitlneta la.BIme Cheese
A sweet, fruit life# flavor develops in cheese of
various types.
If the flatter does mot develop In a
cheese until after it 1* well ripened, it eojarfiosly la
not conspicuous and is not aoverly criticized*
Oca®tonally,
the flavor is noted in young cheese and then it Is am
indication that' fee cheese la not ripening properly*
Pruitineas occurs rather .frequently In domestic him#
cheese*
H u m slight * the defect is not objectionable
to meet people*
General Observations
in general., blue cheese with a fruity flavor .have
a normal appearance*
The defect can be detected 'by
smiling, or tasting the freshly cut surface of the
cheese*.
Shea the defect Is slight, the fruity flavor
seems to blend with the normal flavor of the cheese,
but when it Is pronounced the fruity flavor Is conspicuous.
In young eheea® the defect Is usually associated with a
soft bodyf.whereas in old cheese the defect is present
la cheese, with either a firm or a soft body*
Use presence
©f a yellow green me Id has been noted In some fruity
cheese, tut such a acid has also been noted in cheese
which were mot fruity*
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m
Historical
A fruity flexor it known to occur la various cheeses
sad i® quit# common In cheddar cheese,
Harding, Rogers,
and Smith (14) studied a ”aweetw flavor defeet la Cheddar
cheese end concluded that it was caused by yeasts,
.Mm
outbreak ©f cuts defect In Canadian Cheddar cheese was
studied by 3©©d (15), who attributed It tee the high yeast
content of the cheese.
Experimental
Because of the apparent relationship between a soft
body and high moisture content in cheese and the development
©f a fruity flavor# eight fruity cheese and eight normal
cheese were analyzed for moisture and also for salt* '■Each
cheese represents a different lot and all were obtained from
on-e pleat*
The data are presented In Table 2,
from the results It is evident that the moisture
contents of the fruity cheese were definitely higher' than
those of the normal cheese; the lowest moisture content of
the fruity cheese was higher than the highest moisture
content ©f the normal cheese*' The average moisture contents
of the normal cheese and the fruity cheese were 40.OT per
cent and 46,25 per cent# respectively.
Both the normal
and fruity cheese showed wide variation# in salt content,
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m
fable S*
moisture
Am sopifi
& & m m t contents of sgrkal
AND FRDXTT BLOB CBKXSE
$t
:s..
formal cheese
f
t
Cheeses Per cent: Per cent
number imoi abare t la Cl
fruity cheese
'it '
T'
:: Cheeses Per eent Per centsi numberstnoiatmr#
Wad
IS
. „ t
___
s 41*86
s
4*96
li
1
r 49*76
s 4.56
2
t 42.03
t
4.30
IS
2
s 47*23
t
5
'I 34,71
a
a
4,36
S'S
3
't 46*74
s 5*52
4
r 35.62
f
3,32
S'f
4
s- 45*38
s 4.85
■s
i 39,31
s
3.90
IS
5
t 45*98
4
■6 t 30*44
i
4.46
11
6
I 46*96-
: 4.15
7
'i 44.72
'i
4*68
a
7
■f 45*36
t
8
T
43.00
■t
3.93
IS
8
« 50.17
's. 4*78
i
4.48
it
s 46.25
t 4.60
Ay, I 40.07
■*
1
4*51
4.08
4,60
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50
but such variations are rather regularly noted In him©
cheese fro® various sources *
fh® average salt contents of
the normal cheese and the fruity cheese differed very
little, the values being 4,4S per m m t and 4.60 .per cent,
respectively.
An attempt was made to- duplicate the fruity flavor
defect by making a cheese with a M g b moisture content.
.Sufficient cheese curd was prepared to make three normal
sis# cheese.
Card for two cheese was dipped before It had
firmed in an effort to increase the moisture content.
It
was inoculated with normal powder and handled in the usual
manner.
fi» remaining ctird was allowed to- firm normally
and then dipped and inoculated with normal powder.
After
salting and punching the cheese, were placed in the -curing
room.
User, examined after 5 months the two- experimental
cheese had firm, compact bodies-, -and it was evident that
the attempt to make cheese with a high mole tore content
was- unsuccessful,
fee body was so- firs that mold develop­
ment was not satisfactory except in a few scattered, areas*
The cheese had a nasty flavor, as- Is- eosaaoo when mold
development la. a him# cheese is slow and act abundant.,
the control eheaao. had good-mold' growth and flavor.
Sine® occasional samples of fruity cheese show the
presence of a yellow green aoll, attempts were made to
isolate this microorganism so that Its relationship to
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SI
tli# defect could 'be studied.
Samples of fruity chess#
were plated on tonaate juice, acidified tomato juice, beef
infus lea and Csap#k#s agars*
Si® plates were poured la
duplicate and on# set Incubated at 10^0* and the other at
21°C.
fhe plates were examined after 1 week and P* rogue-
fortl was found on *11 plat##,
lioroerganlsas other than
P. roauefortl ©ccasleasily were noted., especially colonies
of & yeast and of a yellow green mold,
to agar slants and litmus milk-.*
'these were picked
fh# yeast did not ferment
lactose and was not considered further*
’
the yellow green
mold produced a fruity, yeast Ilk® fermentation in litmus
milk which suggested that It might cams® a fruity flavor
in cheese#
A mold powder was prepared with it for use in
experimental cheese*
frlal 1*
.A quantity of blue cheese curd sufficient to make
three S8*$ pound cheese was divided into three lots#
fo
one lot was added normal mold powder« A mixture of normal
and yellow mold powder was added to fee second lot*
fo
the third lot was added only yellow green mold powder*
After salting and pinching the cheese were placed In the
curing room with other' cheese made the same day.
fhe
three cheese were ©a the -end ©f the rack next to the
humidifier end the edges softened somewhat.
The cheese
nearest the humidifier was the control cheese and it
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63
developed more of a soft edge than the others, After
ripening for.2 months the cheese were cut and observed.
The cheese mod® with the mixed powder had s good normal
mold growth and the yellow green mold could not be detec­
ted; it leaked flavor,
The ekeeee islt with the yellow
green mold powder bad some normal a o M growth but it
showed very little flavor| the yellow green mold could
not be detected.
The control cheee# had good mold growth
but lacked flavor*
After a ripening period of 5 months the cheese were
again cut and observed.
Bach cheese had a normal mold
growth and the presence of the yellow green mold could
not be detected*
Both the experimental chseee and also
the control chess® had developed a fruity flavor*
This
was more pronounced in the control cheese than la either
of t he experimental cheese to which the yellow green mold
powder had been added*
All three cheese bad soft bodies,
the body of tbs control che.ee® probably being the softest*
The result# suggest a relationship between a soft body in
blue cheese and a fruity flavor*
Trial 2*
Sufficient curd was prepared to
size cheese and the
again tested.*
make three normal
mold powder# meed in trial 1 were
After ripening for 3 months the cheese were
cut and observed*
The cheese m i s with the mixed powder
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S3
showed & fair 10M gpwtth but no yellow green » M | no
blue cheese flavor coulcl be detected*
only the yellow green w M
fh© cheese made with
powder'had a few small areas of
normal mold hut ho growth of the yellow groan mold j the
eheese 'had not developed a desirable flavor*
fhe control
cheese had a normal mold growth and & flavor characteristic
of unrlpemed blue cheese *
After § months ripening the cheese were again cut
and observed*
fflbe bodies of the- cheese were firmer than
the corresponding small cheese*
fim normal mold, growth
had increased sc^ieidiat in the two experimental cheese,
but the yellow ..green aold m s sot detected*
the mold growth
in the control cheese was essentially the same as at E
months*
Each cheese had developed some blue cheese flavor*
It■was most pronounced la the control choose and least ■
pronounced in. the cheese made with the yellow powder,
A
fruity flavor was not detected in any of the cheese*
Additional attempts to isolate an organism canslag frultineas*
Several additional Samples ©f fruity bine cheese 'were
obtained,
The cheese, were approximately E*§ months of age,
had a good mold growth and 'had developed enough bln® cheese
flavor to bo salable*
Th® bodies of the cheese were softer
than normal., and each eheeee had a dlfinite fruity flavor*
The samples were plated on Cz&pek^s toast© juice, acidified
tomato juice end beef infusion agars*
The plates were
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$4
Incubated at 10®, SI® and 5?®C*
They were examined each
day for several days and very few microorganisms other
then P* roquefortl were observed*
Colonies of the yellow
green mold previously leelated fro® fruity cheese were
net detected*
©teemsSion
In the blue cheese studied, fruitiness most often
occurred la cheese having a high moietmre content, as
shown by general observations on the body of the cheese
and also by analyses*
The failure to isolate an organism capable of pro­
ducing f m i tines s la chess# suggests that the defect may
fee caused fey a variation In the growth products of the
normal blue cheese organisms, as a result of the change
in environment.
There remains th# possibility of 'the
isolation methods failing to yield the causative organism;
most .of the cheese examined were obtained after the
ripening was complete.
Conclusion
A fruity flavor in blue cheese seemed to- be associa­
ted with cheese having a relatively high moisture content*
*0
organism capable of reproducing the defect
could fee
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Si
isolated from the defective cheese, end & yellow green
mold present la souse ©I* the defective sa»ple» did net
eras* fra it in® ss in eh®##®, Although it produced a fruity,
yeast-like odor in milk,
A relatively high moisture content
la cheese may so Influence the activity of the normal blue
oboes# organisms that the growth products deviate somewhat
from the usual type*.
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is
Slack Macolorstoloii of Blue Cheese
Blue cheese 1# eharaeterlsed not only toy.its flavor
tot also toy the bln® w i n # throagh it*
a®' veins are due
to the growth ©f |* roqneforfcl aoA are expected in a normal
cheese,
Molds other than f* roqueforti occasionally invade
blue cheese.
If the color produced toy them Is rather
similar to that of the- normal tolue portions* It is over*
looked* tout if it Is not similar, its presence Is immediately
noticed and it Is designated as a color defeet*
On® ©f the
most noticeable of these color defects is a black discolor*
stolon*
General Observations
Samples of blue cheese having a black discoloration
were received from a coatereial cheese plant*
The cheese
shoved little evidence of normal slime formation, tout
were dry at the surface and had cracked in several places*
the surfaces of the cheese were darker in color than
normal, and the cracks were filled with a black mold
growth*
Cut surface# ©f the cheese showed that there had
been an invasion of the cheese ttore«#i the. punch holes*
They also skewed a penetration of the black discoloration
into part# of the cheese beyond the areas of black mold
growth*
There were many areas of normal mold growth and
the flavor off the cheese was fair , although it tended to
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m
be somewhat masty, especially in tb© discolored'areas*
Sis torleal
Microorganisms are known to cams® various color
defects In chooses*
Investigations have indicated
that bacteria are responsible for most of these*. Lelteh
(17) studied the cans# fot mottling and bleaching in Ched­
dar cheese and con-eludod that bacteria were responsible
and that colon forms accelerated discoloration*
Gruber
(IS) isolated an ©rgaals® causing small red or rust
colored spot# in Worth German hard and cream cheese*
He named It Bacillus easel fusel*
laiini and AiIowan
{26} attributed red spot® in aansstbal cheese to- a
propionic scld organism. Bacillus soldi propionic! var*
ruber*
lurri and Sfcsub (4) described am organism
responsible for red discoloration in ementhal cheese
and named it Bacterium subrufura* According to Davis
and Hsttick (10) Connell obtained the causative organism
from cheddar cheese end maned it Bacillus radons is* Davis
and J&ttlek (10) isolated the causative organism from
eheddar cheese and concluded that it was related to the
common lactic acid organism**
Stocker (24) found a
mold of importance in producing color defects in cheese*
He noted that black spots and dark discolorations on the
rind of soft cheese were dm® to Mon11la nigra*
Dlaeolor-
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m
at Ion is lew Zealand choose was studied beeteriologlcally
"by Morgan (2 2 )j toe noted that tbs muddy discolorations all
occurred near ©racks or openings la fee cheese aad
con*
eluded that they were caused by the growth of molds •
Experimental
Small portions of the defective ©hot## wore plated,
as lag Gz&p9k*s, t o m to Juice sad acidified tomato juie©
agars*
fhe plat®# wore divided into tliroe lot# and
Incubated at 10®, 21® .sat 37*0* the incubation time being
arbitrarily set at 1 week*
An. m & m l m t i o n of tb® plates
incubated at 37° c, showed very few molds and none sug­
gestive of ceasing a black discoloration in cheese*
Many
of fee plates incubated «t li®' ®r 2l°C* showed fee presence
of very dark, mold colonies in addition to- colonies of
P* roquafortl*
Of fee three media, Cs&pek’s agar appeared
t©. be the most favorable for growth of fee dark mold*
Several colonies of the dark sold were pieked to Czapek*©
agar slants and spotted on Csape1ecfl agar plates for further
study*
flating of the original cheese on 0®apek,e agar was
repeated several tine# and in ail eases plates incubated at
10® or 21°C* developed a significant number of very dark
mold colonies*
Several samples of normal blue cheese were plated
on Czapekfs agar and the plates incubated at 10° and 21°G•
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m
After 1 week the plates showed ah occasional contaminating
mold colony, hat home were dark colored or in any way
resembled the mold obtain## from the defective cheese*.
A preliminary exa»iaatlo» ladteeted that all colonies
of the dark mold were similar and were probably the same
species*
The fact that it w m found In significant numbers
in the defective cheese 'hut could not be isolated from
normal cheese led to the assumption- that it was the mold
responsible for the black discoloration*
Mold powder was
made with the. dark M W f,following the usual procedure»
and several trials wore carried out In an attempt to dupli­
cate the- defect.*
Trial 1*
Sufficient him# eh##s# curd to make thro# 2.5 pound
cheese was divided into thro# «f»al portions.
To on# lot
normal f # roquaforfci powder w m sd€«d# in the second lot
& mixture ©f P* rocmefortl and the dark mold powder was
used and to the third lot the dark mold powder was added*
fee lots of curd- were then .handled in the usual manner,
and after salting and punching, the cheese were placed in
the curing room*.
observed.
After 5 months- the cheese- were cut and
The outside- of the cheese containing the dark
mold was dark brown- to- black la color*
The outside
appearance of th* control eh««s# and. the cheese aid# with
the six.®#, powder# was normal *
The oat surface of the
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60
cheese containing the dark mold showed black mold growth
In the pinch holes , giving it a black streaked appearance*
The cheese near the surface and M i t to the psach holes
was discolored*
A slight ssuefcy flavor had developed*
ft,® cut surface of the cheese made with the mixed powders
showed a variation in the color of sold growth*
Certain ■
areas were blue , others dark to blank and some appeared
to be a mixture' of the two*
the black areas in the cheese
were very small and the cheese had not become discolored
outside the black areas*
ffae cut surface of the control
cheese showed only blue mold end was considered normal In
color*
Flavor development was not noted in either mixed
mold chess® or the control*
Trial 1 was repeated with the exception that the
cheese were normal la size*
Ifter ripening period of 3
months the cheese were cut and observed-*. 'Hie outside
appearance of the dark sold cheese differed from that of
the corresponding small cheese*
It first glance the
surface of this cheese appeared quite normal,- but when
the surface slime and mold had been removed, a large number
of punch holes were very noticeable*
They appeared as
regularly spaced black pits in the surface of the cheese.
The cheese in the Immediate vicinity of these pinch holes
had begun to turn dark.
Hie outside appearance of the
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61
control cheese and of the cheese containing the mixed molds
was normal and differed w r y little from that of the sum H e r
cheese of trial 1*
The cub surface of the dark mold cheese
showed: black streaks following the poach holes# and the
cheese surrounding these streak* was dark* 'The dark mold
had not epread through the cheese and was confined to the
'punch holes and openings leading from them*
The flavor of
the cheese was musty and did not in any way resemble blue
cheese*
The cut surface of the cheese containing the mixed
mold powders showed normal blue areas# black areas and
areas In which the mold appeared dark gray*■ The latter
war®' probably caused by the two molds growing in ©lose
proximity*
The flavor of the ©he*®# suggested a combin­
ation ©f blue cheese and musty flavors*
The cut surface
of the control cheese was normal'and the cheese had
developed a fin® flavor-*
Trial 5*
This was a repetition -of trial 2*.
Observations
after 5 months confirmed those of trial 2*.
Identification of dark mold.
Various cultures of the dark mold were studied in-'
considerable detail.
The organism was identified, accor­
ding to the classification of Uilmaa and Abbott (11), as
Hormod endrum ollvacemo.
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@2
2>i«cu«si<m
Under natural conditions the invasion
of blue cheese
by H* oliyactum i s a M be -expected to occur through cracks
and punch holes*
If the texture of' the cheese Is ©-pen,
the mold has a better opportunity to. spread through the
cheese and produce am extensive black discoloration.
Under
experimental conditions the growth of the mold was confined
to the outside of the cheese and to punch holes. ■ This
Indicates that B* ©Itvftosnai requires a good oxygen supply#
from their investigations, -Shea and Currie {25 ) concluded
that the dominance ©f t*. roauefortl In ■the. Interior of
roqnefort cheese Is due pertly to the reduced oxygen content
which favors the growth of the t u m m l sold over other types#
For this reason. Jf* ©ifmcemat. would not be expected to cause
a great deal of spoilage in morsel cheese.
It Is conceiv­
able » however,, that under certain manufacturing conditions,
tm which the cheese had a body particularly susceptible to
cracking , the mold could cause extern*lire damage*
fee musty" flavor produced by g* olivaeeum is of less
importance than the discoloration*
In experimental cheese
made -with & mixture of H* ollvaeeuai and jp* roquefortl . the
flavor of the cheese was not typical but was close enough
t© normal to -satisfy most consumers *'
If the -proper procetmre is followed, in making blue
cheese, and particularly when homogenised milk is used:.
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63
the chees® will have a body that is not susceptible to
cracking » s M if the proper husidity is maintained In the
cubing room, the cheese will not -dry and crack.
Suitable
aumnfaetaring »theds should do siuch toward controlling
the defect,.
Conclusion
I black discoloration and « m a t y flavor in cosiwrcial
blue cheese were attributed to the growth of JU olly&eeum
la the cheese.
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34
dray Blaaoierwtfoa of ■Blue, Cheese
Discoloratless of cheese may be divided Into two
type®, those Involving color only «*ft those involving
flavor sad' color*
Discolorations accompanied by a. flavor
defeel; are the mere aertotus* and the gray discoloration
■of bine cheese belongs i© this ©lass,. ®ie defeat: is
particularly serious beemtee wbeti oaee started, it spreads
through the entire cheese.*
■Seneral 'CJbeervatioms
Gray discoloration of blue cheese commonly is mated
on the surface of the cheese after the ■slime has been
removed by sorapiag or was-Mig*
B m discolored portions
are dark gray in. color s M vary frcm a few snail areas
on some cheese to complete discoloration on others.*
When
defective cheese are cat they'usnally Show a normal mold
growth*
Tim. cut surface of different chess# show
variations in the automat of discoloration*
Ihe defect
appears to have originated on the snrfaee and them to
have spread through the eheeee*
Because of this the
discolored portions evident on cutting' the- cheese vary
from small areas to complete discoloration.
In all
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m-
cases extensive discoloration la accompanied by a mousy,
ttMBoaifteal flavor which has * tendency to become soapy
with age| the off flavor does not appear until the cheese
are several month® old.
The defect seems to be confined
to certain lots of cheese and may or may act include all
the cheese in a lot*
Hair# appears to be no tendency for
the defect to spread from ©me cheese to another*
listorieal
Color defect® ia cheese have been observed and studied
by numerous investigators*
Bark discolorations, in which
either bacteria or certain amino-sold were involved, have
brem noted ia different cheese#*
Golding (12} Investigated an outbreak of eolor defect®
la stilton cheese.
The cheese first turned, yellow bat upon
aging turned red and then black*
Under practical eonditioijs
he found that the addition of large amounts of salt (taCl)
to the curd tended to- favor the defect*
Oxygen had a
tendency to.increase the darkening and from this 'fee suggests
that an oxidase- might be responsible*
This was further
substantiated when heated cheese failed to turn yellow while
chloroform did not stop 'the -©hangs*
The addition of a
solution of tyrosine to the cheese caused it to turn dark*
From this Golding concluded that under certain condition#
tyrosine may be a Halting factor#
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66
Cornish and William (8), working on discolored
stilfcon cheese, isolated aany types of microorganisms and
studied, two groups. The first .group* identified as
Bacillus protemg vtilgarl-a.. pranced a brown color both
In solutions of typtdffeano and ia tryptophan® agar.
In
tyrosine m&la*. however* it ppodoowd -tally a slight dis­
coloration.
The second, group, composed of gram negative,
alkali proimeittg bacilli#.gar® a slight discoloration in
tryptophan® media and turned .tyrosine media a dark brown
or black.
Further studies wore carried out by ?enn {27}
and by Mattlck and William {IS}*
¥©rm used the gram
negative* alkali producing bacilli isolated by Cornish
and Williams and studied the effect of pH color on production
in tyrosine media*
I® found that color was produced between
pi 3*73 and pH 9.7, with the Intensity Increasing a# the
center -of the- rang® was approached,
lettick and Williams
studied, the ’
Bacillus proteus vulgaris Isolated by Cornish
and Wllltsta*
They found teat la typtophane solutions a
color ranging from orange- to. light yellow was produced at
pH Talus# from 8.95 to $*41«
discoloration Is low- .Zealand Cheddar cheese was
Investigated biochemically 'by loir {20} and bacteriologi­
es lly by Morgan (22).
loir found 'teat th® pH of tea rnddy
area# was much higher than that of normal area# In the
same cheese.
Fro® this and other studies hi concluded
that the muddy discoloration Is probably caused by
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67
oxidative enzymes, including. tyrosinase.
Morgan noted that
the middy discoloration occurred near crack# or openings in
the cheese end concluded that it was .caused by the growth
of mold *
The ability of certain microorganisms to produce
black pigments has been studied*
Skinner (23} found that
nearly on©-third of the Aotinoiayces he isolated were capable
of producing a melanin when. grown- m
medium plus tyrosine*
Conn*# complete
Clark and Smith (5} reported that
Baelllua ulster produced a black pigment in protein media
which contain metabolically available tyrosine*
A dark discoloration of cheese due to metals has been
reported- by a number of investigators*
Seed and Whit# (16)
noted that light brows to yellowish brown areas In Cheddar
cheese were due to fragstents of the steel wool which was
used to- ©lean the vat*
Leiteh {17 ) found that black
discoloration In cheddar cheese was due to- lead sulfide,
while a gray -black discoloration was due to iron sulfide
formed under neutral or alkaline conditions*
Davies (9)
reported traces of tin in darkened areas of cheddar cheese
but -considered the lead constituent of the solder to- be
responsible for the color defect*
Barnieoat (1) added
various metals to cheese milk at the rate of from 3 to 7
parts per million*
fh® discolorations- noted with copper
and iron were considered to be due to the atmospheric
oxidation of a. -colorless metal protein complex, while the
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68
discoloration with lead was due to Its sulfides,
Experimental
Several Investigators wfe© have studied discolorations
in cheeses have concluded that the color was dm© to melanins
produced by the action of tyroisinaa© upon tyrosine*
This
suggests that perhaps there ar© microorganisms present in
gray discolored him© chess©, which «r© capable of producing
©telefilms.
lime eheese showing gray discoloration were obtained
end cultured on several different media*
Samples from the
surface aid the Interior of the eheeee were plated on
Czapek’s, torn to Jute#,, acidified, tomato Juice and beef
infusion agars*
The plates were divided into- three lots
and incubated at 10®, 81® ami 8?®8*. .After the colonies
were well developed, they showed a variety of colony types
which Included bacteria, yeasts and molds*
The total
number of microorgani sms differed with each cheese plated*
There was a variation in the flora of the different cheese,
with f. rociuefortl as the only microorganism which was
consistently present on. all plates*
Representative colonies
fro® each plat© were picked into a medium cone5©ting of skim
milk saturated with _1-tyrosine,
fee cultures were divided
into two lots and incubated at' 18® end 2I®8*
Observations
were made each week on the cultures to see whether any of
them were capable -of darkening' the medium.
An occasional
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m
culture produced si alight discoloration but discolorations
were not considered significant and the cultures were
discarded after an Incubation period of' 1 month.*
Additional
samples of gray discolored cheese were plated* and similar
results obtained,
the work of Skinner C85 5 suggests the possibility of
Actinomyces feeing Involved in the discoloration of blue
cheese*
Since blue cheese is usually aide from raw milk*
several samples of such milk were obtained and plated on
beef infusion agar*
The plates were divided end some
incubated at 21®G* and the others at 37°C.
the presence
of Actinomyces was noted on plates from an occasional
sample of milk*
the colonies observed wore of two types,
One typo produced * h w m m itseolorittioii In the medium and
the other did not.
All colonies of Actinomyces were
picked ©a beef infusion agar slopes and when a number of
cultures had been collected they were streaked on plates
of beef infusion agar to- which lad. been added 8 ml, of a
skim milk tyrosine, medium per plate,
‘Tubes of the skim
milk tyrosine'medium were also Inoculated with the organisms*
Some of the cultures were incubated at 10°0, and others at
21°C* .They were observed from time to'time for color
production,
a ® cultures, of AetiaoMaw* which did not
produce a discoloration in the beef infusion agar failed
to- produce a discoloration in the tyrosine media, and all
cultures' of Actinomyces producing a discoloration in beef
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70
infusion agar produced & natch darker discoloration in the
tyrosine media*
Os plates the black discoloration extended,
beyond the. limits of the colony*
In the skim milk tyrosine
medium the color ranged from a black at the surface to "a
dark gray at the bottom*
Tills dark.gray discoloration was
similar to- that found in a defective blue cheese*
Since the gray discoloration in cheese appears to
originate at the surface and progress into- the cheese* an
attempt was made to- reproduce the defect by inoculating
pieces of cheese with the pigment producing Actinomyces,
Portions fro* the surfaces of several normal cheese were
■placed in open mouthed glass containers and inoculated
heavily with the Actinomyces * fhe containers- were then
held in a cooler* similar to m curing room, to determine
whether the Aetionoiayces would grow and produce a gray
discoloration la the cheese*
After a period -of 2 months
no growth of Actinomyces could he detected, and ®s the
cheese showed no signs of discoloration the samples were
discarded,
'the failure of the Actinomyces to grow and produce
a gray discoloration in cheese suggests that conditions
for growth in the cheese were not satisfactory*
Since
'the organisms grew on agar -and in milk with approximately
the same .pi as that found on the surface of a cheese, It
would seem that from this standpoint
medium*
cheese was a favorable
The high salt eon tent of the cheese, however, mlgbt
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71
tee «. fee tap ia preventing fete.© growth ©£ Actinomyces.
Several
plates were prepared mslag beef infusion agar plus 5 ml, ©f
the' skim milk tyrosine medium to whiete had been added
varying amounts of salt,
The plat®# contained approximately
0*00, 0*O1, 0*1, 2*0, S«S and 7*0.per cent salt*
fh® plates
were streaked with pigment producing Actinomyces. Incubated
at 81*0 • and observed each day*
The organisms grew, on- all
fete# plates, and salt concentrations up t© and Including 2*0
per cent seemed to accelerate their grtwtb*
centrations definitely Inhibited growth.
Higher con­
In all eases fete®
organism® produced a black discoloration and this seested
to vary' In direct■proportion to the amount ©f salt,
The
color prodtaetlmi was greater Is each plat® containing salt
than it was in the ©e-ntr©!.
The |M was determined on IS samples of .gray discolored
cheese; in each ease the pH was also determined on a normal
colored portion of the same eh®®#®*
The data are presented
In tabl# 3*
The results show that a variation in pi occurred In
both normal and discolored cheese.
The pi rang® noted in
the normal choose was from 5*25 to 6.72
colored cheese from 6*25 t© 7*29.
and in the dis­
fh® greatest variation
In pH between normal and discolored portions of the same
cheese occurred with cheese 11 and amounted to 2*01 pH
units; the least variation occurred with chess® 2 and
amounted to only 0,14 of a pi unit.
The striking thing
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Table 5 .
pi DKTERMBATICRS OB BORKAL \*U ORAT DISCOBOIS? B O T CHX88B
*
Cheese number
1'
Cray
sdIscolored cheese
t
Bernal eheeae
1
f
*•07
I:
6.S8
2
*
6.11
1
6.25
3
s
6.15
4
s
6*16
f
7.18
■3
t
6.09
I
7,12
§
f
6.72
*
7.02
7
I
6,SO
4
7.05
B
l‘
.
6*IS
9
1
6.52
r
6.85
10
X
6.00
!
6.65
5*25
t
7.29
11
7.12
6.85
12
I
S.56
5
7.22
15
J
5.77
r
7.28
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75
shown by the data Is that In every ease the pi of the
discolored cheese was higher than that of the corresponding
normal cheese and in most case® the difference was signifi­
cant*
Golding (12), In investigating an outbreak of color
defect in atllton cheese, found that large amounts of salt
favored the discoloration-..-
Since atil ton cheese Is some­
what similar to blue cheese this suggests that perhaps
the salt has something to do with the gray discoloration
In blue cheese.
Six samples of defective and six samples of normal
blue cheese were analysed for salt*
Bach cheese repre­
sented a different lot and -all were obtained from the
same plant*,
fable 4 presents the results.
The data show a variation in the salt content of
both normal and defective cheese* The average salt con­
tent of the normal cheese was 5.92 per.cent while that
of the defective cheese was S.54 per ©eat.
The signifi­
cant thing shown by the analyses is that in all cases
the salt content in the defective cheese was considerably
higher than, that of normal cheese.
Four cheese of average size were prepared to deter­
mine whether the gray discoloration could be produced by
a higher salt content*
The cheese were salted in the
-
usual manner and were then placed' In a saturated salt
solution for 72 hours*
The cheese were punched and placed
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74
fable 4*
SGDJBft CiMtlDl COlfSifs OF iorlal All© S M I discolored
BL5S CHEESE
Cheese
number
s
:
t
*
Per cent faCl In
i
Gray
Jformel cheese
t filscolored cheese
a
*
4*80'
*
5*05
8
f
3.60
t
4.55
3.
i
5*95'
t
6.06
4
t
4.08
*
5.8®
5
.»
5*70
5.10
6
f
3. 90
t
t
At *
:
3. m
S
5*34
5.30
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75
in the curing room*
After a ripening period of 5 months
the cheese were cut and observed*
The body of the cheese
was firmer than usual and the wold growth was limited..
The cheese had a fsir flavor but the salt tended to mask
it,
The cheese was not discolored In aay way and even
appeared whiter than normal*
JMacusslotj
The ripening of blue cheese involve# a protein
breakdown,
lormlly this does not. proceed to a point
where the resultlag products affect the flavor of the
cheese in an objectionable way*, in cheese showing gray
discoloration a sonsy,, ammoataeal ©dor commonly was
present and the cheese tended to become soapy with age*
The suggests a relatively large change In reaction, which
is farther Indicated by the pH Measurements on the cheese*.
Presumably, certain lower disintegration products of
protein.® which are basic in character are involved in
the reaction change*
The variation in the normal ripening mechanism
which yield# cheese showing gray discoloration-may be
due to extensive growth of JP, roouefortl since the organism
actively attack# silk protein*
toother possibility is that
contaminating organisms are Involved although non© that
reproduced the defect could be .Isolated*
Certain Actinomyces
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76
cultures produced a darkening in tyrosine media but they
apparently failed to .grow in cheese*
Conclusion
fh© development of gray discoloration in blue cheese
was aeeengMmted by an increase la pS,
Tim variation from
the normal ripening mechanism.' which caused the gray
discoloration presumably involved the formation of basic
products from protein.*
Extensive development of £.
requefertl or .growth of contaminating organisms could
be responsible'for an unusual protein decomposition*
Contaminating organ!ama capable of reproducing the defect
could not be isolated*
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77
R lO A P IT tJM ffO l OP CCHCM3fSIO»» Off TH t VAHICBJS BEPS0TS
A defect of blue cheese in which m portion of the
edges
became soft appeared to be caused by excessive moisture
in the softened part ©f the cheese.
The defect was readily
reproduced by placing cheese near « humidifier- where free
moisture could strike It*
§m» formation Is of relatively little importance la
blue cheese,, presumably because of the ©pea texture, which
permits the gas to escape, end the unfavorable conditions
la the cheese for growth of the common gas forming organisms.
frisls with m -culture of Aerobacten aerogenes freshly Isolated
from gassy c-heddar cheese showed that Inoculations {of the .
milk) which resulted in- very gassy chuddar cheese caused no
gas holes or only tnslgntfleant .numbers- in blue cheese*
A- defect of blue cheese in which the blue sold failed
to develop In the cheese was apparently caused by the use
of a mold powder ia which an atypical strain ©f Panicilllum
roanefortl predominated,
the variation ia the mold may have
been caused by the- ■long continued cultivation on an artifi­
cial medium of the culture used to prepare the powder.
A fruity flavor "la blue cheese seemed to be- associated
with a relatively high moisture- content.
So organism
capable of reproducing the defect could be isolated from
the defective cheese, and s yellow green mold present la
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78
some of the -defective samples did not cause fruitiness in
cheese, although it produced a fruity, yeast like odor in ■
milk*
A relatively high moisture content in cheese may
so influence the activity of the normal "blue cheese
organisms that the growth product* deviate somewhat from
the usual type.
A black discoloration « M a musty flavor in com­
mercial blue cheese -were attributed to the growth of
Horiaodendrum olivaceum in the cheese*
A defect in which a gray discoloration and a mousy,
ammoniaeal flavor developed in blue cheese was accompanied
by an increase in pi.
The variation from the normal
ripening mechanism which caused the .gray discoloration
■presumably Involved the formation, of basic products frost
protein*
SKtonsivo development of fenlcllllum recmefertl
or growth of contaminating organlams could be responsible
for an unusual protein decomposition.*
Contaminating
organisms capable of reproducing the defect could not be
Isolated*
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
ACJOIQBI2D9SKSB TS
The anther* wishes to express his sincere appreciation
for the assistance and ■suggestions gltren by Dr. B. W.
lawier is the experimental studies and preparation of this
thesis| to- Dr. M.- P* Baker for his assistance la the
preparation of the photographs f to Br. 3» C. Gilman for
his assistance ia identifying certain sold culturesj sad
to Mr. ?* I* Sielsen for his cooperation in certain phases
©f the laboratory work.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
80
tTimmmm
cvsbd
1*
Bemleoet, C. E. The effect of certain metallic
contaminants on the ©heddar cheese making
process. Jour , Dairy M m # 8:53-60. 108?.,
2*
Bergty's Manual of Determinative Bacteriology 5th
Edition, Willisas and Wilkins 0©-, Baltimore,
10. If39.
8,
Biourge, H u X*» aoletssures du group© PenlclIlium
link, la Cellule, 33:7-335, 1925.
4.
Burri, R, and St&ub, W,
5.
Clark, F* 1. and Smith, S, R. Cultural requirements
for the production of black pigments by bacilli.
Jour* Bact. 37:277-284. 1939.
Sin® eigenartlge dureh
Bakerlen bewirkte Rotfarbung in Emmentalerkase.
Landw. Jahrb. Schweiz. 40:1006-1011. 1926,
fi. Cornish, E, V. C. and Williams, R. S. Colour changes'
produced by two groups of bacteria upon eeseinogen
and certain amino-acid®, Bloehea. Jour.
11:180-187. 1917.
7,
Dairy Science Association. Committee on microbiological
methods of examining butter. The microbiological
analysis of butter* Jour* Dairy Sei. 16:889-299,
1933.
8,
Dairy Science Association. Subcommittee for the analysis
of cheese. Determination of fat, moisture, and salt
In hard cheese. Jour* Dairy Sol, 20:87-30, 1937..
9,
Davies, W. L. Detection ia situ of tin solder causing
dark discoloration la cheese. Analyst, 57:95-96.
1932.
10.
Davis, J. 9. sad Hattick, A* f. ft* lusty spot in
cheddar and other ©Mesa. Jour. Dairy Rea.
1:50-57. 1989,
11.
Oilman, J. C* and Abbott, 1. V. A summary of the soil
fungi. Iowa State 'College Jour, of Scl, 1:225-345.
1927,
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81
12*
Soldlag* Jf* fallow discoloration of stiltoa cheats*
Jour. Bd* Agr* (Stagland)-, 19 :177-186, If12*
IS*
©rubor, Th* Seber die TTrsach* dor br&unroten- Plrbung
von Hart-und feichklsea. Genthi* fun Bakb* Abt,
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Herding, K. A*, Rogers, L. A., and Smith, £J* A,
Notps on some dairy troubles. I, Y. (feneva),
Agr, Ixp, Sta, Bui. 185. If00,
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Hood, 1, 0. Sosas factors relating to injurious flavors
in cheese. Butter-nod Oheese lour, 20:18*
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Hood, B» 0, nnC. White, A. H, A case of metallic
discoloration of cheddar choose, Set. Agr*
10:520-522. 1950.
1*7.
Leiteh, 1. H* Cheddar Cheese-Maklag, Faults in
Cheese, the Scottish Agricultural Publishing
Company limited* 1952,
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Isrshsll, C. I, ©assy curd and cheese*
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iahtiek, 1* C* V. and Williams, 1. S, The Influence
of reaction on colour changes la tryptophan
solution*. Biochem. Jour# 15:213-215. 1921.
lleh. Agr*
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A. and Ward., A, R, An inquiry concerning
. Moore,theV.source
of gas and taint producing bacteria
0. M. Discoloration in Sew 2oaland cheddar
cheese, Middy, bleached, and pink defects.
Jour. Dairy Res. 4:233-245* 1953.
in cheese curd.
Bui. 158. 1899
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H. Y. (Cornell), Agr. Sap* Sta.
3, P. Y. Discoloration in lew Zealand Cheddar
, Morgan,
cheese* Middy, pink, and bleached defects* Jour.
Dairy Res, 4:226-237. 1933.
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. Skinner,
Aetinoayeetes, Jour. Beet* 55:415-424. 1958.
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Stocker, W* tFber balcterlelle SchwarsfSrbungen des
Easerltid©, Centbl. fur Bskt* Abt. 2.
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82
25.
thorn, C. and Currie* J. I. Hi© dominance of roquefort
mold In eiieese, Jour. Biol* Cheat. 15:249-258*
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ffaoai, J. **k I Alleiaart, 0.
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ll. iS':i6-51*
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changes ia tyrosine solutions. Biochem. Jour.
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Whitehead,-&* It. The influence of bacilli of the
colon group on ©fceddar eheeee. Jour. Dairy
See* 2*76-80. 1950.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.