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Changes in the Viscosity of Cultured Buttermilk during Commercial Filling.

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Dev.Chem. Eng. Mineral Process., 7(la),pp. 17-23. 1999.
Changes in the Viscosity of Cultured
Buttermilk during Commercial Filling
F. Butler
Dept. of Agricultural and Food Engineering, University College
Dublin, Earlsfort Terrace, Dublin 2, IRELAND
~~~~~~~~~~~~~~
Changes in the consistency of cultured buttermilk caused by filling into cartons was
investigated by comparing the viscosity of commercial buttermilk before and ajier
filling. Two different cartonfilling systems were investigated. One system caused long
term significant reduction in the viscosity of the buttermilk compared to samples
taken directly from the storage tank The secondfilling system caused no significant
change in viscosi@. The results demonstrate that with care and proper design of
equipment, products such as buttermilk that are sensitive to shearing can be filled
with minimum damage to the product.
Introduction
A previous paper [I] demonstrated that the viscosity of cultured buttermilk exhibited
time dependent shear thinning behaviour. During commercial production, once the
product has been fermented and a protein gel structure formed, there is a possibility
that the delicate structure of buttermik can be damaged during subsequent cooling
and filling [2]. The effect on viscosity of cultured dairy products of processing
parameters such as heat treatment 131, 141, [ 5 ] and homogenisation pressure [6] have
been reported. Hauge et al. [7] studied the effect of pumping method on cultured
milk products. However no published work is available on the effect of commercial
filling on the viscosityof products such as yoghurt or buttermilk.
This paper
17
F. Butler
investigates structural damage to buttermilk during filIing by comparing the viscosity
of buttermilk Wore and after filling by two filling methods. This work has important
commercial considerations as buttermilk viscosity or consistency is an important
product attribute influencing a consumer’s decision to purchase.
Experimental
Two carton filling systems were studied Both filling systems were fed from the same
10,000 1 storage tank The first was a Tetra Brik TB9 system. (Tetra Lad AB.
Lux4 Sweden), filling one liee cartons.The product was pumped approximately 40
m from the storage tank to the filling machine through 50 mm diameter stainless
steel piping. Two pumps were in the line, a gear pump (Model CL 1/20, Howard
Pwnp Oompany, Sussex, UK) at the exit of the tank and a cennifugd pump (puma
size 38-50 mm, APV, Crawley, UK) at the W g machine. The second pump mas
necessary to maintain sufficient pressure witbin the filling machine. Product was
medinto the carton through a 25 mm diameter filling head
The second filling system was a Tetra Rex TR7 system, (Tetra Laval AE3. Lund..
Sweden) Wing 500 ml cartons. The product was conveyed through approximately
40 m of 50 mm diameter stainless steel piping Only the gear pump mentioned above
was required to pump the product. Cartons were filledthrough a 50 mm filling pipe.
Samples of cultured buttermilk were obtained directly from a commercial dairy.
As buttermilk texture can vary significantly from one day‘s production to the next, all
samples were taken from the same batch. Samples of the cooled buttermilk after
fermentation were taken directly from the 10,000 1 storage tank by long W e d
dipper into wide necked 1 1 glass jars. Twenty 500 ml cartons of buttermiIk were
taken directly after filling Itom the Tetra Rex filling system and twenty 1 1 cartons
were taken fiom the Tetra Brk All sampleswere subsequently stored in a chill room
at 4 OC until required. All measurements took place in the subsequent three days
after receipt of the samples.
The pH of the buttermiik samples were monitored over the three days of testing
using a Phillips PW 9410 pH meter (Phillips EIectronics. Netherlands) equipped
18
Changes in the viscosiry of cultured buttermilk
with a Pye
- Ingold combination pH electrode. AU
samples were measured in
duplicate each day. Total solids content was determined by evaporation of the water
h m a test sample in the presence of zinc oxide at a temperature of 102
OC
according to IDF standard 151 [8]. Protein content was detemined by the Kjeldahl
method (model KB20 Kjeldatherm System, Gerbarct&Bonn Swikerland). A total of
18 total solids and protein measurements were carried out over the period of testing.
Fat content was measured using the Gerber test to IS. 67 [9]. In total 6 fat content
measurements were carried out.
Constant shear rate tests at two shear rates were used to masure the time
dependent viscosity of buttermilk preliminary experimental work had indicated that
the viscosity of buttermilk changed slowly over its shelf life of 15
- 20 days. This
most likely arose from continued slow microbial activity. As a consequence testing
was limited to a threeday period after receipt of samples. In order to obtain suflicient
test replicates in that period, only two shear rates, 25 and 300 s-l, were used. The
period of shear was 20 minutes. Each viscosity measurement was replicated ten times
for all treatments. V i i t y measurements were carried out in a Physica Systems
Rheolab MC 100 Rheometer (Physica Mef3technij.cGmML Stuttgart, Germany) fitted
with a double gap concentric cylinder to DIN 53019.1 [lo]. The m d n g cup had
an inside diameter of 44.5 mm and a 48 mm outside diameter. The rotating bob had
an h e r and outer diameter of 45.5 and 47 mm respectively. The submerged length
of the bob was 111 mm. The test cylinder was filled by carefidly pouring a fresh
sample of buttermilk into the cylinder. After filling, the meaSaring bob was lowered
into the sample and the test cylinder and sample were left to equilibrate for 15
minutes prim to testing. Temperature control was by circulating water bath, All
measurements took place at 5 O C f 0.2 OC. Data mas recorded every 4 seconds
during shearing. Significantdifferences in viscosity was tested by canying out a one
way amiysis of variance on viscosity r d t s for the same time period from the start
of testing. This was repeated for each time period Where a significant effect was
deuxkd, differences between treatment means were tested using the Ieast sigtuticant
Merence test.
19
F. Butler
Results and Discussion
Table 1 gives a summary ofthe total solids, protein and fat content of the buttermilk
for each of the three treatments. The results were typical of a commercially produced
bu#ennilk. As expected, one way analysis of variance showed no significant
d i f k m c e s between treatments. Table 2 gives the variation in pH in the samples over
the measuring period. A two way analysis of variance showed no significant
Werence in the pH between treatments, but indicated a small but sigmfkant drop (P
< 0.01) in pH over the three days of measurement. This was a t & i W to a slow
COIltjnuaton in microbialactivity in the buttermilk.
Toble 1. Total solia3, protein andfat content of the buttermilk samples employed in
the study
Storage
Tetra Rex
Tetra Brik
Tank
Filler
Filler
Total Solids Content (% w/w)
8.5
8.5
8.6
Protein Content (% wfw)
3.3
3.3
3.3
< 0.1
<O.l
KO.1
Sample
Fat Content (YO
w/w)
Toblp 2
. Variation of pH during the period of testing of the buttermilk samples
employed in the snrdy
Storage
Tetra Rex
Tetra Brik
Tank
Filler
Filler
Day1
4.59
4.60
4.58
4.59
DaY 2
4.55
4.56
4.57
4.56
Day3
4.51
4.54
4.52
4.52
Average
4.55
4.57
4.55
sample
Average
Figures 1 and 2 show the average viscosiv of the buttemilk Samples taken from
the storage tank and from cartons filled by the Tetra Rex and Tetra Brik filling
systems as a function of time of shear at a constant shear rate of 25 and 300 s-l
20
Changes in the viscosiry of cultured buttermilk
respectively. In all cases the buttermilk exhibited time dependent rheologcal
bebaviour with the ViscosiF decreasing by between 29% to 45% over the 20 minute
test perid This was a similar result to previously reported work [ 11. More of interest
was the s i m c a n t dif€erence (P < 0. 01) at both shear rates and all time intervals
between the buUermiik filled into the Tetra Brik cartons and the buttermilk in the
Tetra Rex cartonsor the samples taken from the storage tank.
v
1-
m
3
0.1 *<
.B 0.05 *.
Tetra Rex
Tetra Brik
9
Figrcre 1. Average viscosity of buttermilk samples at 5
OC
taken porn the storage
tank and fiom cartons filled by the Tetra Rex and Tetra Brik filling systems as a
firnction of time of shear at a constant shear rate of25 s-]. Data was recorded e v e v
4 seconh.
Surprisingly there was no significant Merence in viscosity between samples
taken from the Tetra Rex cartons and the storage tank at any time period during
measurement. Some reduction in viscosity would have been expected arising from
the shear the product would have experienced during pumping and filling. Benezech
and Maingonnat [ l l ] stated that it is generally admitted that yoghurt. a similar
cultured dairy product to buttermilk, exhibits an irreversible time dependent effect.
Ramaswamy and Basak [12] reported that the thixotropic structural breakdown of
21
F. Butler
However in that study the
samples were I& for a recovery period of only one hour before remeasurement. In
yoghurt following shearing was almost irreversible.
this study the samples were left at least overnight before measurement so it is
possible that this holding time allowed the structure to recover.
1
0.05 I
Tetra Brik
>8
.
I
0-
Figwre 2. Average viscosi& of buttermilk samples at 5 OC taken porn the storage
tank and porn cartons filled by the Tetra Rex and Tetra Brik filling vstems as a
finction of time of shear at a constant shear rate of 300 s-I. Data was recorded
every 4 seconds.
The main difference between the two filling systems was the presence of the
centrifugal pump in the Tetra Brik system. Hauge et al[T found that centrifugal
pumps caused more damage to the viscosity of cultured millcs than positive
displacement pumps. Centrifugai pumps exert high shear rates (approximately lo3
s-’ ) on the pdwts passing through them [13]. This would cause si@cant
stmctud breakdown in the product. While some recovery might have taken place
with time. sufficient structural damage took place to explain the reduction in
viscosity of the buttentdk in the Tetra Brik cartons as compared to the Tetra Rex
cartons or the storage tank
22
Changes in the viscosity of cultured buttermilk
Conclusion
The Tetra Brik filling system caused long term si@cant
reduction in the viscosity
of the buttermilk compared to the Tetra Rex system or samples taken directly from
the storage tank It was most likeiy that this reduction arose mainly from the
presence of a centrifugal pump used to mainlain sufiitient pressure in the Tetra Brik
filling machine. The results demonstrate that with care and proper Besign and choice
of equipment, products such as buttermilk that are sensitive to shearing can be filled
with minimum damage to the product.
References
1. Butler, F.. and McNulty, P. 1995. Time depeadmt Ifieological charaderidon of butmmdk
'
at 5 "C. J.
Food h
g
.
.25,569-580.
AH., and Shafand, J.P. 1994. Milk ipld d k produds k&101wmanistry.
,
and
2. V~RWZU
M i c r o b i ~ l ~(g3
~-.
& €Id,
Loadon.360 361.
12.6-7.
3. Meikljohu,P.G. 19n.H~toamievebetteryogb~~.CCulCuredDairyRociuctsJ.,
4. Latnqmulos, AE.; Collins W.F.,and Stmc, W.K 1984. Effects of ultrs.higb tanpaature and vat
prarsrc~CII heat-incbuad h d ~ @
p m p a i Of
~ yo@- J. Dairy Sci., 67,40549.
5. Kartpnli M 1993.
ofthe diffaent had treatmmts on rbevbgical and ag~lolepticalprogetis of
y @ w J. of Dairying 12.8-16.
6. Lia. C.A. a d Rib, EL. 1995. Effsa of hmwgwbtiar pressure and miIk ompsiti- (10 the
visasky of yogut 3. Darq sd.78,149,1995.
7.
S.S.; Oteholtn, B., and Solbug P. 1974. cbunid and physical propaties of athued milks as
iafiucllced by prrmpingID&&
XIX Intrmaricad D& Con1E 739-740.
8. Rovinimal IDF stasldard 151.1991. Yogrnt dd
. "an of tual solids CcQtalL
9. LS. 67.1955. Dctammstl
'
'arofthepumtageofkm~mikmdbutemik
10. DIN 53019.1. 1980. V
i , Dctammatl
. 'on ofviscoSitig and tlow CUNS usiugstsmdard desim
witha~dardgcomcrrymessuring~
11. BenaeQ T.,and Mabgnmat J.F. 1994. mean of Rba~logicalProptics of Yo@
A
~cvisw.J. ~ o ~ d ~21,447
n g , 472.
12. Ramanvamy,,. S.,adBasakS. 1991. R h e O I O g v o f s 6 T # i y ~J. OfTSmneStUdi~22.231-241.
13. Elam- H.A.Hublan, J.F., and W a h , K 1989. An iatroduction to rheology. Elsevia. Amshadam 1213.
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