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J Sci Food Agric 1997, 75, 244È250
Textural Changes of Banana and Plantain Pulp
during Ripening
Silas T A R Kajuna,1 Walter K Bilanski2 and Gauri S Mittal2*
1 Department of Agricultural Engineering, Sokoine University of Agriculture, PO Box 3003, Morogoro,
Tanzania
2 School of Engineering, University of Guelph, Guelph, Ontario, Canada, N1G 2W1
(Received 30 April 1996 ; revised version received 18 February 1997 ; accepted 14 March 1997)
Abstract : Green banana and plantain fruits were treated with ethylene or kept
untreated, then stored in environmental chambers at 13, 16, 20 and 25¡C for 8
days. On daily basis, cylindrical samples of the fruits were compressed twice at
50 mm min~1 to 75% of the original height. Changes in the textural properties
were estimated by the texture proüle analysis (TPA) technique, involving such
parameters as hardness, chewiness, guminess, cohesiveness, springiness. Storage
time signiücantly reduced all TPA parameters except cohesiveness. Untreated
bananas were harder than untreated plantains at all stages of storage. In treated
fruits, however, the trend was reversed, and bananas softened more than plantains. Generally, treated fruits resulted in reduced TPA parameters as compared
to untreated fruits. Untreated fruits of both varieties had a good correlation
between pH and hardness-1 while treated fruits did not show any correlation
between the two properties.
J Sci Food Agric 75, 244–250 (1997)
No. of Figures : 3. No. of Tables : 6. No. of References : 11
Key words : banana, plantain, texture, ripening, ageing
treated with caution and such a modulus is termed
apparent modulus of elasticity or modulus of deformability (Mohsenin and Mittal 1977). The latter modulus
considers both recoverable and non-recoverable deformations that take place when a food sample is subjected
to even very small strains. The actual modulus of elasticity may be obtained by cyclic loading within the
elastic limit, and taking the slope of the ürst unloading
curve.
The apparent modulus of elasticity was measured
(Ramaswamy and Tung 1989) by compression tests on
ripening banana. The modulus of elasticity has been
used by some researchers to represent the ürmness of
fruits (Finney et al 1967). The textural aspects of plantain have received little attention in the literature, and
the available data based on objective measurements can
hardly be sufficient for providing optimum texture for
ripeness (Peleg and Brito 1977). Therefore, the objectives of this study were (i) to investigate and compare
the textural properties of bananas and plantains as
aþected by the ripening process, and (ii) to correlate the
INTRODUCTION
Texture is a major division of sensory quality in food
products. It is limited to the sensation of touch or feel
by the human hand and mouth parts. This property
may be determined both subjectively and objectively.
The objective techniques have the advantage over subjective ones in that they are precisely reproducible. One
of the methods that have been employed in analyzing
the textural properties of food materials is the texture
proüle analysis (TPA).
Young’s modulus of elasticity can be obtained as the
slope of the compressive stress–strain curve within the
linear region. Most agricultural materials are viscoelastic (Mohsenin 1986), exhibiting both ýow and
deformation properties. Therefore, the modulus of elasticity obtained for agricultural materials must be
* To whom correspondence should be addressed.
Contract grant sponsor : International Development Research
Centre, Ottawa, Canada.
244
( 1997 SCI.
J Sci Food Agric 0022-5142/97/$17.50.
Printed in Great Britain
T extural changes of banana and plantain
change in hardness with the change in pH during the
ripening process.
MATERIALS AND METHODS
Fruits of two cultivars namely, bananas of the Cavendish sub-group (Musa AAA Group) and plantains, of
the plantain sub-group (Musa AAB Group) were
acquired in three diþerent shipments from Costa Rica
through a fruit dealer (Meloripe Banana Company,
Toronto, Canada) between May and July 1993. Each
shipment represented a replication for the experiment.
When they arrived to Toronto, they looked green and
were estimated at stage 1 on the colour ripening chart.
The bananas were in cartons of 18·2 kg while plantains
were in cartons of 11·4 kg each. The fruits stayed in the
warehouse of the dealer for 3 days from receiving date
to the delivery date. Twenty cartons of bananas (half of
them ethylene treated) and 32 cartons of plantains (half
of them treated) were delivered to the University by a
truck (1 h drive). The ethylene treated fruits were
treated with 1000 ppm ethylene for 24 h in air tight
rooms at room temperature (B20¡C). Thus preliminary
transportation treatment was same on all the batches
used for the research. There was no visible transportation damage to the fruits. Upon arrival at Guelph, the
fruits were estimated to be between stages 1 and 2 (dark
to medium green) on the standard colour ripening chart
(Banana Retail Guide of Del Monte Tropical Fruit
Company, USA).
All fruits were stored at four diþerent temperatures
in 8 separate environmental chambers with the relative
humidity controlled at 90 ^ 4%. The variables were
ethylene treatment (treated, untreated), cultivar
(bananas and plantains), temperature (13, 16, 20 and
25¡C), and storage time (days 1 to 8). Day 1 was considered after storage for 24 h at the desired temperature. The fruits were removed daily from the
storage chambers and allowed to equilibrate to ambient
temperature (B20¡C) for about 30 min. Cylindrical
samples of size 20 mm diameter by 20 mm long were
taken from the fruit pulp along the longitudinal axis,
using a cork borer. Samples were taken from approximately the same central position of the fruit, and each
sample being taken from a diþerent fruit. The TPA test
was carried out on a universal testing machine (Model
4024, Instron Canada Ltd, Burlington, Ontario,
Canada). Two compressions, each to 75% of the original height of the sample were done at a crosshead
speed of 50 mm min~1. Force–time data were collected
on a personal computer through IEEE and a BASIC
software. The software logged 10 data sets per second.
Three samples were taken from each treatment and the
whole experiment was replicated three times. Thus,
there was a total of 1152 tests involving an equal
number of fruits (ie 2 ethylene treated or untreated
245
(gas) ] 2 varieties (var) ] 4 temperature levels
(temp) ] 8 days ] 3 samples ] 3 replications (rep)).
The pH was determined by inserting the probe of a pH
meter (Accumet model 925-Fisher Scientiüc Co, USA)
into the pulp of the fruit and recording the pH readings.
The following TPA parameters were then calculated
(Fig 1). Hardness-1 (H1, N) refers to the ürst peak
before the compressive plate reverses direction and
hardness-2 (H2, N) is represented by the force at the
second peak on the force deformation curve. Cohesiveness (COH) is the strength of the internal bonds
making up a food material, and is represented by the
ratio of the area under the second curve, (A2) to the
area under the ürst curve, (A1). Gumminess (GUM, N)
is the force required to disintegrate a semisolid food to
a state ready for swallowing, and is a product of
hardness-1 and cohesiveness. Springiness (SPGN, cm) is
also referred to as elasticity, and is deüned as the rate at
which a deformed food material goes back to its undeformed condition after the deforming force is removed.
On the TPA curve, it is represented by the distance on
the abscissa, from the point where the loading plate
touches the food sample during the second bite to the
point corresponding to hardness-2. Chewiness (CHEW,
N cm) is the energy required to masticate a solid food
Fig 1. Typical texture proüle plot for (a) untreated plantain
pulp stored at 13¡C for 1 day, and (b) treated banana pulp
stored at 16¡C for 2 days.
S T A R Kajuna, W K Bilanski, G S Mittal
246
product to a state ready for swallowing, and is product
of the hardness-1, cohesiveness and springiness.
The apparent modulus of elasticity was also computed as the slope of the ürst compressive stress–strain
curve within the linear region. The data were analysed
(SAS 1988) using analysis of variance (ANOVA), least
square diþerence (LSD) and correlation (CORR) procedures. The general linear model (GLM) procedure of
the SAS was used to perform a split-plot analysis.
There was one restriction on randomisation as storage
days were selected after selecting other treatment
parameters—ethylene treatment and storage temperature. Ethylene treatment and storage temperature
were randomised. The whole experiment was repeated
twice.
RESULTS AND DISCUSSION
Replication and interaction eþ ects
The replication eþect was not signiücant at 1% level for
all the TPA parameters, except springiness, at 5% level
(Table 1). Most of the three-way interaction eþects
were not signiücant except for SPGN (P \ 0·01).
Ethylene eþ ect
The ethylene treatment to banana and plantain fruits
had a signiücant eþect on all the TPA parameters
(Table 1). Temperature did not show signiücance on
any of the parameters as an individual factor. However,
it aþected through interaction with gas and replication.
This therefore suggests that the eþect of temperature on
the hardness or texture of banana and plantain fruits
during storage depended on whether fruits were treated
or not. At the end of the 8-day storage period, treated
bananas at the temperature of 25¡C had started to rot
while those at 13¡C were still hard and ürm, with a
large blend of green colour with yellow (ie more green
than yellow). Since each replication represented a different batch of the fruits, there could possibly be some
diþerences in maturity from batch to batch. This could
perhaps inýuence the way the fruit responds to ethylene
at diþerent temperatures. Associated with the batch to
batch variation is perhaps the time the fruits were harvested or the time period taken for the fruits to be
transported from the source (farms) to the market. The
data showed a trend for the temperature inýuence on
the hardness, with fruits becoming softer at higher temperatures than lower temperatures. However, this trend
was greatly aþected by ethylene treatment. There was a
more uniform texture of the fruit pulp (for both
bananas and plantains) in treated fruits than in
untreated fruits. Therefore, ethylene treatment would
be encouraged where uniform texture of the fruits is the
marketing strategy. In climacteric fruits, the greater the
concentration of ethylene the faster the stimulation of
respiration (Pantastico 1975). However it is more eþective when applied during the pre-climacteric stage. The
application of ethylene signiücantly aþects the time
scale required to reach the climacteric peak. In climacteric fruits like bananas, ethylene acts only to shift the
time axis, it does not alter the shape of the respiratory
curve.
TABLE 1
Split-plot ANOVA showing the mean sum of squares (MS) for TPA parametersa,b
Source
df
H1
H2 (]10~5)
COH
GUM
SPGN (]10~2)
CHEW
Modulus
6
2324**
17
31
65
6140**
45
22
1·4*
38·3**
0·4
0·2
19·1
981·0**
6·6
4·0
4·3
277·3**
1·9
0·5
Test of the hypothesis using var ] day ] gas ] temp as error term
Var
1
5330
42142**
942**
Day
7
49381**
16667**
4
Var ] day
7
9526**
1592**
16**
Var ] gas
1
47304**
74719**
1647**
Var ] temp
3
1542
941
12*
Gas ] day
7
2321
1313
16**
Temp ] day
21
1171
557
4
Var ] temp ] day
21
510
210
2
Var ] gas ] temp
3
1927
792
9
Gas ] temp ] day
21
1320
637
5
Var ] gas ] day
7
2079
379
3
633**
101**
5
909**
11
14*
5
2
9
6
1
42·4**
0·5*
0·3
16·8**
0·6*
0·1
0·1
0·1
0·3
0·1
0·6*
62·9**
15·5**
1·6
115·3**
2·4
3·7*
0·8
0·3
2·2
0·9
0·5
11·2**
6·5**
0·9*
20·9**
0·2
0·4
0·1
0·1
0·2
0·1
0·3
Test of hypothesis using rep ] gas ] temp as error term
Rep
2
36209
11752
Gas
1
1787802**
867385**
Temp
3
11660
6030
Gas ] temp
3
3118
2017
a Abbreviations : df, degree of freedom ; rep, replication ; temp, storage temperature ; gas, ethylene treated or untreated.
b Level of signiücance : * P \ 0·05, ** P \ 0·01.
T extural changes of banana and plantain
247
H1 had a mean of 191 N for bananas while it was
161 N for plantains (Table 2). On the contrary, in
treated fruits, plantains had H1 of 47 N while that of
bananas was 32 N. Thus, for the ürst bite, untreated
bananas would require more energy than untreated
plantains. After ethylene treatment, however, plantains
would require more energy than bananas, signifying
that bananas soften more with ethylene treatment than
plantains. For the second bite (H2), Table 2 shows a
trend similar to that of H1, except that lower energy
would be spent in biting the food sample. As reported
elsewhere (Pitt 1992) the major modes of failure in fruit
and vegetable tissues are cell rupture and cell debonding, therefore untreated plantain pulp would suþer
more cell rupture and cell de-bonding on the ürst and
second bites than untreated banana pulp. But once ethylene is applied, the energy requirement would be
reversed.
Cohesiveness, which is a measure of the strength of
the internal bonds of the food material was signiücantly
higher for untreated bananas than for untreated plantains (Table 2), also supporting the argument above,
that more energy would be required for de-bonding the
Ethylene treatment also interacted with the variety
(Table 1) to cause a signiücant eþect on all the TPA
parameters. It also interacted with storage time to cause
a signiücant eþect on COH, GUM and CHEW. The
mean values for the response of the TPA parameters
for the var ] gas interactions are shown in Tables 2
and 3. For untreated fruits, the response variables H1,
H2, COH, GUM, CHEW and modulus of elasticity
(modulus) were consistently higher for bananas than
plantains, except the springiness (SPGN) which was
higher (except for day 2 and 4) in untreated plantains
than untreated bananas. For treated fruits, these variables (including SPGN) were consistently higher in
plantains than in bananas ; further underlining the
eþect of interaction between gas and variety. Ethylene
had a greater softening eþect on banana than plantain.
Variety eþect
Hardness-1 was not inýuenced by variety, but was
inýuenced by the interaction between variety and ethylene treatment (var ] gas). However, all other TPA
parameters were inýuenced by the variety and
var ] gas interaction (Table 1). For untreated fruits,
TABLE 2
Comparison of pulp’s textural parameters between treated and untreated bananas and plantains [var ] gas]a
Untreated
H1 (N)
H2 (N)
COH
GUM (N)
CHEW (N cm)
Modulus (MPa)
Ethylene treated
Bananas
Plantains
Bananas
Plantains
191 ^ 41
142 ^ 33
0·062 ^ 0·011
12·2 ^ 3·8
4·6 ^ 1·6
2·6 ^ 0·5
161 ^ 92
94 ^ 54
0·039 ^ 0·006
6·6 ^ 4·2
2·7 ^ 1·8
1·7 ^ 1·0
32 ^ 32
20 ^ 22
0·034 ^ 0·005
1·2 ^ 1·1
0·3 ^ 0·4
0·4 ^ 0·4
47 ^ 45
27 ^ 25
0·037 ^ 0·004
1·7 ^ 1·6
0·6 ^ 0·5
0·5 ^ 0·5
a The data are the averages of 96 observations ^ SD.
TABLE 3
Comparison of springiness (SPGN, cm) in treated and untreated bananas and plantains at diþerent storage times
[var ] gas ] day]a
Days
Bananas
Plantains
Untreated
1
2
3
4
5
6
7
8
Treated
Untreated
Treated
Mean
SD
Mean
SD
Mean
SD
Mean
SD
0·358
0·410
0·375
0·396
0·364
0·367
0·355
0·355
0·019
0·056
0·027
0·069
0·036
0·054
0·053
0·032
0·286
0·283
0·285
0·272
0·258
0·246
0·246
0·263
0·006
0·037
0·017
0·032
0·016
0·024
0·034
0·039
0·436
0·394
0·416
0·393
0·379
0·370
0·381
0·407
0·020
0·050
0·041
0·048
0·036
0·048
0·048
0·047
0·366
0·366
0·365
0·388
0·367
0·390
0·382
0·381
0·053
0·048
0·049
0·045
0·039
0·033
0·032
0·033
a The data are the averages of 12 observations.
S T A R Kajuna, W K Bilanski, G S Mittal
248
pulp of untreated bananas than that of untreated plantains. Similarly, gumminess which is a measure of the
force to disintegrate the particles ready for swallowing
was also higher for untreated bananas that it was for
untreated plantains (Table 2). The eþect was reversed
when the fruits were treated.
Springiness, which is a measure of the recovery in
height after the sample has been compressed by the
teeth during mastication, was higher in both untreated
and treated plantains than in untreated and treated
bananas (Table 3). This suggests that although
untreated bananas may require more mastication
energy in the mouth for the ürst and second bites than
untreated plantains, they may not spring back as much
as plantains. There was a var ] temp interaction eþect
on springiness of the pulp (Tables 1 and 4) which
showed that at each temperature, springiness was
higher for plantains than it was for bananas.
Chewiness, which is the energy for masticating the
food product until it is ready for swallowing, was
higher in untreated bananas than in untreated plantains
(Table 2) and the trend was again reversed for treated
pulp. This further supports the earlier observations for
H1, H2 and GUM. The elastic modulus which is a
measure of ürmness (Finney et al 1967) was higher in
untreated banana than in untreated plantain with the
trend being reversed in treated fruits (Table 2).
The pulp rupture force in three untreated cultivars of
plantains and one untreated cultivar of Cavendish
bananas at 20¡C was compared (Marriott et al 1981).
They reported that rupture force for unripe banana
pulp was higher (25·5 N) than the rupture force in the
pulp of two of the three plantain cultivars (23·1 and
25·0 N). Only one plantain cultivar showed a higher
pulp rupture force (27·5 N). However, once ripening
commenced, the rupture force in plantains was always
higher than that of bananas. This supports the results
of this study that untreated banana pulp had a harder
texture than that of untreated plantains.
Storage time or ripening eþect
The storage or ripening time (days) had a signiücant
eþect on all the TPA parameters except cohesiveness. It
also interacted with variety to aþect all the TPA
parameters except gumminess and chewiness (Tables 1
and 5). There was also a gas ] day interaction eþect on
cohesiveness, gumminess and chewiness (Tables 1 and
6). As well, there was a three-way interaction eþect
(var ] gas ] day) on springiness (Tables 1 and 3). On
day 1, plantains started with higher H1 and H2 than
TABLE 4
Comparison of cohesiveness (COH) and springiness (SPGN) for various temperatures for bananas and plantains [var ] temp
interaction]a
Variety
Temperature level (¡C)
13
Banana
Plantain
16
20
25
COH
SPGN (cm)
COH
SPGN (cm)
COH
SPGN (cm)
COH
SPGN (cm)
0·049 ^ 0·017
0·038 ^ 0·006
0·33 ^ 0·06
0·38 ^ 0·04
0·050 ^ 0·019
0·038 ^ 0·005
0·33 ^ 0·07
0·38 ^ 0·04
0·047 ^ 0·016
0·038 ^ 0·005
0·32 ^ 0·08
0·39 ^ 0·05
0·045 ^ 0·015
0·038 ^ 0·005
0·30 ^ 0·06
0·39 ^ 0·05
a The data are the averages (^SD) of 48 observations including ethylene treated and untreated.
TABLE 5
Comparison of textural parameters between bananas and plantains at diþerent storage times [var ] day interaction]a
Storage day
1
2
3
4
5
6
7
8
Bananas
Plantains
H1 (N)
H2 (N)
COH
Modulus
(MPa)
H1 (N)
H2 (N)
COH
Modulus
(MPa)
151 ^ 73
122 ^ 86
113 ^ 91
112 ^ 85
104 ^ 90
97 ^ 89
99 ^ 93
95 ^ 90
108 ^ 59
91 ^ 69
83 ^ 71
83 ^ 67
75 ^ 69
69 ^ 67
71 ^ 70
67 ^ 67
0·051 ^ 0·020
0·051 ^ 0·018
0·049 ^ 0·019
0·050 ^ 0·017
0·046 ^ 0·016
0·045 ^ 0·015
0·046 ^ 0·016
0·046 ^ 0·015
1·97 ^ 0·87
1·62 ^ 1·16
1·52 ^ 1·24
1·48 ^ 1·17
1·40 ^ 1·27
1·29 ^ 1·25
1·29 ^ 1·26
1·23 ^ 1·24
203 ^ 78
135 ^ 95
111 ^ 94
85 ^ 81
87 ^ 87
69 ^ 71
71 ^ 78
72 ^ 76
109 ^ 45
80 ^ 58
66 ^ 58
49 ^ 48
52 ^ 52
41 ^ 44
42 ^ 46
42 ^ 43
0·036 ^ 0·006
0·037 ^ 0·006
0·038 ^ 0·007
0·037 ^ 0·004
0·039 ^ 0·004
0·037 ^ 0·004
0·039 ^ 0·003
0·039 ^ 0·004
2·20 ^ 0·84
1·49 ^ 0·98
1·23 ^ 1·05
0·95 ^ 0·94
0·92 ^ 0·93
0·74 ^ 0·82
0·77 ^ 0·86
0·78 ^ 0·86
a The data are the averages (^SD) of 24 observations including ethylene treated and untreated.
T extural changes of banana and plantain
249
TABLE 6
Comparison of the cohesiveness (COH), gumminess (GUM) and chewiness (CHEW) between treated and untreated pulp at
diþerent storage times [gas ] day interaction]a
Untreated
1
2
3
4
5
6
7
8
Ethylene treated
COH
GUM (N)
CHEW (N cm)
COH
GUM (N)
CHEW (N cm)
0·054 ^ 0·018
0·054 ^ 0·016
0·053 ^ 0·015
0·051 ^ 0·016
0·050 ^ 0·012
0·047 ^ 0·013
0·049 ^ 0·013
0·048 ^ 0·013
12·8 ^ 4·1
11·1 ^ 4·1
10·5 ^ 4·4
9·0 ^ 4·9
8·8 ^ 4·7
7·4 ^ 4·7
8·1 ^ 5·3
7·6 ^ 4·8
4·99 ^ 1·43
4·57 ^ 1·95
4·16 ^ 1·73
3·59 ^ 2·06
3·28 ^ 1·79
2·84 ^ 1·92
2·98 ^ 1·97
2·90 ^ 1·80
0·033 ^ 0·005
0·034 ^ 0·004
0·034 ^ 0·004
0·037 ^ 0·006
0·036 ^ 0·005
0·035 ^ 0·004
0·036 ^ 0·005
0·036 ^ 0·005
3·9 ^ 2·1
1·9 ^ 1·7
1·0 ^ 0·6
1·2 ^ 1·3
0·9 ^ 0·5
0·8 ^ 0·3
0·8 ^ 0·3
0·8 ^ 0·3
1·29 ^ 0·71
0·63 ^ 0·57
0·35 ^ 0·21
0·41 ^ 0·36
0·29 ^ 0·17
0·26 ^ 0·15
0·25 ^ 0·14
0·26 ^ 0·15
a The data are the averages (^SD) of 24 observations.
bananas (Table 5) but softened faster than bananas to
end up with lower H1 and H2 than bananas. The LSD
test (SAS 1988) showed (data not given) that H1 for all
fruits decreased signiücantly for the ürst 4 days in
storage from 177 to 98 N. After that there was a
gradual non-signiücant decrease in H1 to the value of
83 N on day 8. For bananas, it decreased from 151 N
on day 1 to 95 N on day 8, while for plantains, it
decreased from 203 N on day 1 to 72 N on day 8
(Table 5). This suggests that for bananas and plantains
in storage, there is a faster rate of decrease in ürmness
in the ürst 4 days than in the subsequent storage
period. Thus, any marketing strategy would have to
aim at disposing of the bananas and plantains within
that period to avoid the possible loss. Since the softening of the banana and plantain fruits is accompanied by
the hydrolysis of starch to sugars by the amylases and
phosphorylases (Agravante et al 1990), there is less and
less substrate remaining to be acted on in the last days
of storage, perhaps a reason why the decrease in hardness was less signiücant. Agravante et al (1990) also
observed that in bananas, there was a rapid increase in
the total sugars at the initial stages of ripening when the
peel started to turn yellow, and slowed down at the
later stages. This agrees with the observation in this
study, of the rapid decrease in H1 in early days of the
storage of treated plantains, and a slower decrease in
the later storage days. The eþect of storage time on H2
followed a trend similar to that of H1 (Table 2).
Storage time as a factor, had no signiücant eþect
(P [ 0·05) on cohesiveness, but a signiücant eþect was
observed through interaction. Gumminess decreased
signiücantly from 8·4 N on day 1 to 5·1 N on day 4 for
all the fruits. From there on, the decrease was nonsigniücant until the last day when it was about 4·0 N
(data not shown). But considering the interaction
eþects, Table 6 shows that untreated fruits started oþ
with higher gumminess of 12·8 N (about 4 times) than
treated fruits (3·9 N) after day 1. Similar eþect was
observed for cohesiveness and chewiness. After 8-days
storage time, untreated fruits ended up with about 10
times higher gumminess (7·6 N) than treated fruits
(0·8 N). From the three-way interaction of var ]
gas ] day (Table 3) it can be seen that treated fruits
had less springiness than untreated fruits. Plantains had
generally higher springiness than bananas, and the LSD
test showed that springiness was higher in the ürst 4
days than in the remaining 4 days, but there was no
signiücant diþerence between the ürst 4 days and the
last 4 days of storage.
Modulus of elasticity
The modulus of elasticity decreased with storage time
for both treated and untreated fruits (Table 5). This
observation matches that of Finney et al (1967) who
reported that during ripening of bananas, there is a
decrease in starch content of the pulp which was also
correlated to the elastic modulus of the fruit. Hydrolysis of starch to sugar during ripening causes an
increase in osmotic pressure in the banana pulp. The
increase in the osmotic pressure is usually associated
with a decrease in turgor pressure which may account
for softening during ripening, and would cause the
elastic modulus to decrease (Finney et al 1967). A
similar trend of decrease in the modulus of elasticity
with ripeness has been reported in blueberries (Bower
and Rohrbach 1976).
Correlation of H1 with pH
Plantain pulp was more acidic than banana pulp, and
in both varieties, the acidity increased with storage
time. As seen in Fig 2, there was a linear trend, between
H1 and pH. Regression analysis showed a low (0·36)
coefficient of determination, indicating that there may
not be a strong linear relationship between H1 and pH
250
S T A R Kajuna, W K Bilanski, G S Mittal
samples remained on the higher end of the scale. Like
in bananas, the scatter in treated plantains did not
show any strong relationship between pH and H1.
CONCLUSIONS
Fig 2. Correlation between pH and hardness 1 (H1) in
untreated bananas. Y \ 4·96 ] 0·003X. R2 \ 0·36. Each
point is a mean of 3 observations.
in untreated bananas. However, there was a distinct
pattern showing that higher values of H1 tended to
occur with higher values of pH. This implies that when
the fruits were harder, they were less acidic and became
more acidic as they softened. Also untreated fruits
tended to have higher pH (less acidic) throughout the
storage period, which reýects higher H1 values.
In treated bananas, there was no deünite relationship
between pH and H1. However, it will be seen, contrary
to the results in Fig 2, that most of the samples tested
had a mean value on the lower end of the H1 scale,
which supports the softening of the pulp due to ethylene treatment.
Plantains showed a stronger linear relationship
between pH and H1 (Fig 3). The scatter was more uniformly distributed over the entire range of the H1 scale
as compared to what was observed in untreated
bananas. Thus, plantains softened faster than bananas.
In fact it will be seen, comparing Figs 2 and 3 that
towards the end of storage time, a reasonably good
number of samples had shifted towards the lower end
of the H1 scale in plantains while for bananas, more
Fig 3. Correlation between pH and hardness 1 (H1) in
untreated plantains during storage. Y \ 4·61 ] 0·004X.
R2 \ 0·73. Each point is a mean of 3 observations.
Storage time signiücantly reduced all TPA parameters
except cohesiveness. Based on these parameters, except
springiness, untreated bananas were harder than
untreated plantains at all stages of storage. In treated
fruits, the trend was reversed, and bananas softened
more than plantains. Ethylene treatment resulted in
reduced TPA parameters as compared to untreated
fruits. Plantain pulp started with higher H1 and H2
than bananas on day 1, but softened faster to end up
with lower H1 and H2 than bananas. Untreated fruits
of both varieties had a good correlation between pH
and H1 while treated fruits did not show any correlation between the two properties.
ACKNOWLEDGEMENTS
The ünancial assistance in the study by the International Development Research Centre, Ottawa, Canada is
hereby appreciated.
REFERENCES
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