Statistical optimization of process parameters for gelatinization of potato (chandramukhi variety)

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 02 Issue: 11 | Nov-2013, Available @ http://www.ijret.org 170
STATISTICAL OPTIMIZATION OF PROCESS PARAMETERS FOR
GELATINIZATION OF POTATO (CHANDRAMUKHI VARIETY)
Sreemoyee Chakraborty1
, Soumitra Banerjee2
, Saikat Mazumder3
1, 2, 3
Department of Food Technology, TIFAC-CORE, Techno India, West Bengal, India
sreemoyee.chakraborty1989@gmail.com, bitsouban04@yahoo.co.in, saikat.23.1989@gmail.com
Abstract
Potato, a cost effective source of starch, a root vegetable is grown in more than 100 countries in the world. India holds 2nd
position in
potato production in the world and West Bengal 1st
position in India. Potato is processed into a variety of products ranging from
potato powder, potato starch, frozen potato flakes, baby food and alcohol, potato chips, French fries, potato flakes/powder etc.
In this study, the main objective was statistical optimization of the condition for potato gelatinization and effect of potassium
metabisulphite (KMS) concentration on potato starch in gelatinization process. The range of the factors employed were gelatinization
pressure, time and different concentration of KMS. The optimized gelatinization condition was 10psig for 15 minutes and 200ppm
KMS. The percentage of gelatinized starch at optimized gelatinized condition was 35.67 (dry weight basis). Optimization of effective
concentration of potassium metabisulphite (KMS) to retain the colour of potato was also studied and the optimized effective
concentration of KMS to retain the colour was 200ppm. RSM modeling, simple regression was used as a tool to study different
interactive and linear effect of different factors and significance of the factors.
Keywords: potato starch, gelatinization, KMS concentration, colour retention, RSM modeling, regression equation.
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1. INTRODUCTION
Potato in India is cultivated in approx 18-19 lakh hector which
is around 21.9% of the total vegetable cultivated area. It
contributed around 2.41% of GDP of agriculture in 2008 from
1.25% cultivated area. West Bengal contributed around 32%
of the total production in India in 2010-2011(Source: Indian
Agriculture Database, 2011).
Potato starch is unique in that it contains phosphate ester
groups (0.2–0.4% of the glucose units) [1], covalently linked
to AP mainly at the C-6 (61%) and C-3 (38%) positions with
small levels on the C-2 position [2]. It consists of amylopectin
[AP, a highly branched α-(1,4)-glucan with 5% α-(1,6)- bonds,
MW= 1.7*108
for wild type potato starch (wtps), 2.0*108
for
amylose free potato starch (amfps),] [3], amylose (AM, a
nearly linear α-(1,4)-glucan, molecular weight (MW) = 1.03
*106
for wtps) [4].
Gelatinization is regarded as the hydration and irreversible
swelling of the granule, the destruction of molecular order
within the starch granule, and starch solubilization and can
also be interpreted as the melting of starch crystals [5, 6]
Additionally the presence of alkali, salts, sugars, lipids,
alcohol, organic acids and their salts have an impact on the
gelatinization temperature and thus affect the extent of
gelatinization [5]. In the presence of sodium chloride, the
gelatinization enthalpy decreases with increasing salt
concentration whereas the gelatinization temperature rises at
NaCl concentrations up to 2M [7, 8].
Salts also have been shown to have a significant effect on the
gelatinization and rheological properties of starches generally,
and it has been found that they can cause an elevation or
depression of the gelatinization temperature, Tp, as well as
gelatinization enthalpy, ΔH [9, 10, 11, 12, 13], and similarly
might increase or decrease the rate and degree of gelation [14]
and retrogradation ([15, 16]
Peeled potatoes are cut in the form of slices, dices, and strips
before blanching. After potatoes are cut in desirable form, they
are blanched by heating, either in steam or hot water (930
to
1000
C). Blanching destroys or inactivates enzymes; otherwise,
potatoes may darken during dehydration and develop off-
flavors and off-odors during storage. Blanching also serves to
reduce microbial contaminations and affects the way the
dehydrated product reconstitutes. Degree of blanching has a
very marked effect on the texture and appearance of finished
product as well as on the way the potato tissue dehydrates and
reconstitutes. The potatoes are sulfided immediately after
blanching using sodium sulfite, sodium bisulfite, sodium
metabisulfite, or combinations. Sulfite protects the product
from non-enzymatic browning or scorching during
dehydration and increases the storage life of the product under
adverse temperature conditions [17].

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In this study, gelatinization of potato is the function of
pressure, time and concentration potassium meta-bisulphite
(KMS). The parameters were optimized in this study. Another
study of retention or change in colour of potato with different
concentration of KMS was performed to determine the
required effectiveness of KMS in blanching along with 2%
sodium chloride (NaCl).
The easiest and most widely used approach to study linear and
interaction of different factors have been response surface
methodology (RSM). RSM is a collection of mathematical
and, statistical technique useful for analyzing and optimizing
the response of multivariate system. In RSM, generally
attempts are made to identify the responses of system as a
function of explanatory variables. In this study, different linear
and interactive effect of different factors has been studied.
2. MATERIAL & METHODS
2.1 Materials
Collection and Preparation of Raw Materials
Potatoes used in this study were of Chandramukhi variety
collected from local market of South Kolkata. The potato
samples were washed properly with running tap water and
distilled water respectively to make it free from dirt and soil
and followed by removal of excess surface water with a clean
dry muslin cloth. The potatoes samples were then peeled and
sliced into slices of equal thickness of 10±0.3 mm each and
used for farther experiments.
The chemicals used in this study are of “MERCK”, α-amylase
(activity- 10unit/mg) was collected form “SRL” and
Amyloglucosidase aqueous solution (300unit/ml) was
collected from “Sigma Aldrich co. (Novo Enzymes
Corporation)”.
2.2 Methods
2.2.1 Proximate Analysis of Raw Potato
Moisture content, ash content, crude fiber content, starch
content and sugar content of the raw potato was done
according to A.O.A.C method.
2.2.2 Determination of Percentage of Gelatinized
Starch in Blanched Potato Mash
The peeled potato samples were blanched in hot water
(temperature- 900
±20
C) containing 2% of sodium chloride
(NaCl) and varying concentrations of potassium
metabisulphite (200ppm, 400ppm, 600ppm respectively) and
without KMS for 10 minutes and followed by preparation of
mash in a mixer grinder. After that 2 gm mashed sample was
taken from each blanching case and gelatinized starch was
determined according to the method Chiang and Johnson
(1977) [18] followed by dextrose equivalent titration method
for determination of gelatinized starch.
2.2.3 Optimization of Potassium Metabisulphite
(KMS) Concentrations for Colour Retention
The peeled potato samples were blanched in hot water
(temperature- 900
±20
C) containing 2% of sodium chloride
(NaCl) and without KMS and with varying concentrations of
potassium metabisulphite (200ppm, 400ppm, 600ppm
respectively) for 10 minutes. After blanching potato samples
were placed in air tight container and stored at 40
C. The
changes in colour were studied by Hunter Lab Colorimeter for
1 hour interval for first 6hrs and then at 24 and 26 hrs
respectively.
Another study was carried out with optimized concentration of
potassium metabisulphite (KMS) that was successfully
retaining the colour at best. The optimized concentration was
applied in blanching (for 10 minutes) of potato with 2%
sodium chloride (NaCl) and then potato mash was prepared in
a mixer grinder and gelatinized at optimized gelatinization
condition (i.e. optimized time-temperature profile). The potato
mash was stored in air tight container at 40
C for 5 days. The
changes in colour were studied by Hunter Lab Colorimeter for
5 days.
2.2.4 Optimization of Gelatinization Parameters
Production of gelatinized mass was done on the basis of
variation of gelatinization pressure-time profile. The
experiments were carried out on the basis of experimental
design at 33
and 32
full factorial design. Functional effect of
interacting factors (i.e. pressure, time, and KMS) was studied.
KMS was used in this optimization to see whether it has any
effect on gelatinization or not, without the retention of colour.
The blanched slices without KMS and with different
concentration of KMS were mashed in a mixer grinder and
mash was prepared. The potato mash was gelatinized in an
autoclave at different time (10 minutes, 15 minutes, and 20
minutes) and pressure (5 psig, 10 psig, and 15 psig) and KMS
(0ppm, 200ppm, 400ppm, and 600ppm) profile and
gelatinized samples were withdrawn for measurement of
gelatinized starch to optimize gelatinization parameters.
Similar samples were taken for measurement of total starch.
2.2.4.1 Design of the Experiment
The factorial design with three levels of treatment
temperature, time and concentration of KMS was assigned for
33
full factorial designs and three level of temperature, time,
for 32
full factorial designs in case of blanching without KMS
and the design leads to 27 sets and 9 sets of experiments
respectively. The factorial design was applied to estimate the

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relationship between variables on gelatinization of potato
starch. The three range level of factors are 5psig, 10psig,
15psig for pressure (-1, 0, +1 level respectively), 10minutes,
15minutes, 20minutes for time (-1, 0, +1 level respectively),
200ppm, 400ppm, 600ppm for concentration of KMS (-1, 0,
+1 level respectively).
2.2.5 Hunter Lab Colorimeter study
The colour changes of the potato slices blanched with different
concentration of KMS was studied using Hunter Lab
Colorimeter (Color flex, 45/0 spec photometer). The color
readings were expressed by CIE coordinates (L*a*b*) system.
L*(varying from 0-black to 100-white), a*(varying from -60
to +60) and b*(varying from -60 to +60) indicates
whiteness/darkness, redness/greenness, blueness/yellowness
values, respectively.
The polar coordinate chroma or saturation (c*) is an indication
of how vivid the product is (ranging from 0-60), which can be
calculated from the L*a* and b* Cartesian co-ordinate by the
expression
C*= (a*2
+b*2
)0.5
……………………………………..……. (1)
Total color difference (ΔE) was calculated from the following
equation [19]
ΔE= [(L*-L standard) 2
+ (a*-a standard) 2
+ (b*-b standard) 2
]0.5
….. (2)
The retention of colour of potato mash that was prepared from
potato slices blanched for 10 minutes with 2% sodium
chloride (NaCl) and with optimized concentration of KMS and
stored at 40
C also has been carried out using Hunter Lab
Colorimeter (Color flex, 45/0 spec photometer). The total
colour difference (ΔE) and polar coordinate chroma (C*) was
calculated from the L*, a*, b* values respectively.
2.2.6 Assay method of Total Starch and Gelatinized
Starch
Total starch was determined by modified Chiang and Johnson
(1977) [18] method followed by Dextrose Equivalent titration
method. Gelatinized starch content was determined by
Dextrose Equivalent titration method.
Preparation of Enzymes
Preparation of phosphate buffer: 49.7ml 1molar K2HPO4
solution was mixed with 50.3ml of 1 molar KH2PO4 solution
to prepare 100ml of buffer at pH 7.0
Preparation of α-amylase solution (4unit/ml): 4mg of α-
amylase was weighed and mixed with 10ml of phosphate
buffer and stored at 4o
C.
Preparation of Amyloglucosidase solution (4unit/ml): 2ml of
amyloglucosidase was pipetted out and mixed with 150ml of
phosphate buffer and stored at 40
C.
2.2.6.1 Determination of Total Starch
2gm of gelatinized sample was measured accurately and
transferred to a conical flask, 3ml distilled water and 1 ml of
1(N) NaOH was added to it. The conical flask was then
incubated at 600
C for 30 minutes with continuous shaking.
Then neutralization was done by 1(N) HCl. Afterwards, 1ml
of α-amylase solution (4unit/ml) and 8ml of glucoamylase
solution (4unit/ml) was added to conical flask. After proper
mixing of the contents, the conical flask was incubated in a
hot water bath for 30 minutes at 400
C with occasionally
shaking. After that, the enzymes were inactivated by holding
the conical flask in boiling water for about 1-2 minutes. The
final volume is measured. The enzymes break the starch to
reducing sugar which was then estimated by Lane- Eynon
method i.e. by Dextrose Equivalent titration method. The steps
described above were repeated for each gelatinized sample of
different pressure-time profile. These derived data were
subsequently used to evaluate the total starch content of
potato.
2.2.6.2 Determination of Gelatinized Starch
2gm of gelatinized sample was measured accurately and
transferred to a conical flask and 5ml distilled water was
added to it. Then 1ml of α-amylase solution (4unit/ml) and
8ml of glucoamylase solution (4unit/ml) was added to the
conical flask. After proper mixing of the contents, the test tube
was incubated in a hot water bath for 30 minutes at 400
C with
occasionally shaking. After that, the enzymes were inactivated
by holding the conical flask in boiling water for about 1-2
minutes. The final volume is measured. The enzymes break
the starch to reducing sugar which was then estimated by
Lane- Eynon method i.e. by Dextrose Equivalent titration
method. The steps described above were repeated for each
gelatinized sample of different pressure-time profile. These
derived data were subsequently used to evaluate the
optimization of gelatinization condition potato.
2.2.6.3 Dextrose Equivalent Titration Method
Materials:
 Standard dextrose solution: (2mg/ml)
 Fehling reagent: (Fehling A & Fehling B solution)
 Methylene blue
Method:
 1ml of Fehling A and 1ml of Fehling B was pipetted
out in a conical flask.
 The solution was heated to boil.

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 The solution was titrated against standard dextrose
solution until brick red colour developed using
methylene blue as indicator and burette reading was
recorded.
Again the first two steps were followed for different samples
for determination of reducing sugar and titrated against
different samples and burette reading was recorded.
Calculation:
% of total starch/gelatinized starch = [{(burette reading for
standard titration*2)/burette reading for sample
titration}*volume of content in conical flask*100*0.9]/weight
of sample taken.
2.2.7 Localization of Optimum Condition for
Gelatinized Starch Production
In localization study contour plots were obtained by using
Statistica (version 7) (StatSoft, Inc.,USA). The Contour plot
describing combined effect between pair of factors (i.e.
pressure, time) on gelatinized potato starch was given in figure
2 by keeping other two variables constant at their middle level.
2.2.8 Determination of Regression Equation
2.2.8.1 RSM Modeling
The response surface methodology (RSM) was used as it
helped to reduce the number of experiments without affecting
the accuracy of results and to decide interaction effects of
independent variables on the responses [20].
Functional relationships between the independent variables
(temperature, pressure) and dependent variables (%
gelatinized starch), in case of gelatinization, and independent
variable (time) and dependent variable (total colour difference
(ΔE), Polar Co-ordinate Chroma respectively) for potato slices
blanched with NaCl (2%) and optimized KMS concentration
were determined using multiple regression technique by fitting
second order regression equation [21] of the following type
n n n n-1
Y=βo + ∑ βi Xi + ∑ βii Xi
2
+ ∑ ∑ βij Xi Xj + e…….……….. (3)
i=1 i=1 i=1 j=i+1
where β0, βi, βii, βij are regression coefficients of variables for
intercept, linear, quadratic and interaction terms, respectively,
Xi, Xj are the independent variables, Y is the dependent
variables n is number of independent variables.
The relationships between the responses were judged by
correlation coefficients of determination (R2
). The significance
or P-value was decided at a probability level of 0.05.
2.2.8.2 Simple Regression
A simple regression in between dependent variable (total
colour difference (ΔE)) and independent variable (time) has
been determined for potato mash prepared from potato slices
blanched with 2% NaCl and optimized concentration of KMS,
using the first order regression equation of following type
Y= a + bX………………………………………………….. (4)
Where, a, and b is the intercept and slope respectively, and Y
is dependent variables and X is independent variables. The
relationships between the responses were judged by
correlation coefficients of determination (R2
). The significance
or P-value was decided at a probability level of 0.05.
3. RESULTS & DISCUSSIONS
3.1 Proximate Composition of Raw Potato
All the parameters of proximate analysis were done in
triplicate times.
Table 1: Proximate Composition of Potato
Parameters Raw Potato (%)
Wet basis Dry basis
Moisture 82.34 ± 0.27 -
Ash 1.1377 ± 0.14 6.4421± 0.79
Crude Fiber 3.0844 ± 0.08 17.4654 ± 0.45
Starch 12.3547 ± 0.44 69.9586 ± 2.49
Starch percentage was calculated from standard maltose curve
(Fig: 1) given below
Fig 1: Standard Maltose Curve
3.2 Determination of Percentage of Gelatinized
Starch in Blanched Potato Mash
From the data of table 2 it was very clear that gelatinized
starch is very low in potato after blanching and there are very
close differences in percentage of gelatinized starch.

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Table 2: Percentage of gelatinized starch in blanched potato
mash
Concentration of
KMS
(ppm)
Time
(minutes)
Pressure
(psig)
% of Gelatinized
Starch*
0 0 0 8.10
200 0 0 9.9
400 0 0 8.49
600 0 0 9.38
* Dry weight basis
3.3 Optimization of Potassium Metabisulphite (KMS)
Concentrations for Colour Retention
The blanching was carried out without KMS and with three
different concentrations of KMS (200, 400, and 600
respectively), and it was found that 200ppm was the optimized
condition (Table: 5) for retention of colour in blanched potato
sample.
The optimized concentration of KMS i.e. 200ppm was
successfully retaining the colour the potato mash and very
little changes in colour was obtained (Table: 6).
3.4 Optimization of Gelatinization Parameters
Gelatinization experiments were carried out on the basis of
experimental design at 33
and 32
full factorial design. The
factors were concentration of KMS, pressure, gelatinization
time. The results (Table: 3 and Table: 4) shows that %
gelatinized starch is obtained best at 10 psig for 15 minutes.
The results also show that at higher temperature and pressure
and gelatinized starch percentage reduced means the change in
pressure of autoclaving is observed to have an effect on yield
percentage of gelatinized starch.
Initially when the pressure increases from 5psig to 10psig
there is an increase in yield but with further increase in
pressure to 15psig there is a decrease in yield. In this context it
is to be noted that with increase in pressure is accompanied by
an increase in temperature which is a key player in
gelatinization which is previously described by Hoseney, 1986
[22] according to Hoseney, 1986 [22] in order to enhance the
solubility of starches, the temperature must be raised.
Temperature also plays a vital role in retrogradation of starch.
With increase in temperature and pressure more and more
starch micelles initially burst to take part in gelatinization of
starch but with continued increase in temperature/pressure
water continues to evaporate from the matrix leading to a
change in enthalpy of the product and effecting the water
holding capacity of the gel which disintegrates resulting in
retrogradation of starch and in turn decrease in gelatinized
starch percentage.
Another probable cause maybe excess bisulphate of KMS (i.e.
in case of 400ppm, 600ppm) may react with water or water
vapour at higher pressure and temperature and produce
sulphuric acid and the sulphuric acid reacts with the
carbohydrate and produces furfural group.
Table 3: Percentage of gelatinized starch of 33
full factorial
design experiments
3**(3-0) full factorial design, 1 block , 27 runs
Standard
run
Kms
(ppm)
Pressure
(Psig)
Time
(Minutes)
% gelatinized starch
(dry wt. basis)
1 200.0000 5.00000 10.00000 11.89
2 200.0000 5.00000 15.00000 13.72
3 200.0000 5.00000 20.00000 11.89
4 200.0000 10.00000 10.00000 22.29
5 200.0000 10.00000 15.00000 35.67
6 200.0000 10.00000 20.00000 25.48
7 200.0000 15.00000 10.00000 19.81
8 200.0000 15.00000 15.00000 19.81
9 200.0000 15.00000 20.00000 17.83
10 400.0000 5.00000 10.00000 12.74
11 400.0000 5.00000 15.00000 8.9
12 400.0000 5.00000 20.00000 8.9
13 400.0000 10.00000 10.00000 22.29
14 400.0000 10.00000 15.00000 27.44
15 400.0000 10.00000 20.00000 29.72
16 400.0000 15.00000 10.00000 17.83
17 400.0000 15.00000 15.00000 17.83
18 400.0000 15.00000 20.00000 17.83
19 600.0000 5.00000 10.00000 14.86
20 600.0000 5.00000 15.00000 11.15
21 600.0000 5.00000 20.00000 12.74
22 600.0000 10.00000 10.00000 25.48
23 600.0000 10.00000 15.00000 25.48
24 600.0000 10.00000 20.00000 25.48
25 600.0000 15.00000 10.00000 17.83
26 600.0000 15.00000 15.00000 19.81
27 600.0000 15.00000 20.00000 17.83

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Table 4: Percentage of gelatinized starch of 32
full factorial
design experiments
3**(2-0) full factorial design, 1 block , 9 runs
Standard
Run
Pressure
(Psig)
Time
(Minutes)
% gelatinized Starch
(dry wt. basis)
1 5.00000 10.00000 11.15
2 5.00000 15.00000 8.9
3 5.00000 20.00000 7.1
4 10.00000 10.00000 29.72
5 10.00000 15.00000 27.44
6 10.00000 20.00000 25.48
7 15.00000 10.00000 14.86
8 15.00000 15.00000 17.83
9 15.00000 20.00000 16.22
The total starch was simultaneously studied in each case of
time-temperature-KMS concentration profile. The total starch
was found 73%±3% (dry wt. basis).
3.5 Localization of Optimum Condition for
Gelatinized Starch Production
Fig- 2 indicates that percentage of gelatinized starch yield (dry
wt. basis) as a function of pressure and time. It indicates that
the percentage of gelatinized starch yield (dry wt. basis)
concentration maximum at middle level of pressure and
Temperature.
3D Contour Plot
25
20
15
10
5
4 6 8 10 12 14 16
Pressure (Psig)
8
10
12
14
16
18
20
22
Time(Minutes)
Fig 2: Contour plot of the combined effect of pressure and
time on % gelatinized starch (dry wt. basis) concentration
3.6 Hunter Lab Colorimeter Study
Determination of colour retention or changes can be an index
for determination the effectiveness of blanching (with KMS)
in prevention of browning and scorching during storage at
40
C.
3.6.1 Study of Change in Colour of Potato Slices with
Change in Concentration of Potassium
metabisulphite (KMS)
The data Table: 5 shows the value of L*, a*, b* of potato
slices blanched with 2% NaCl and 200ppm, 400ppm, and
600ppm concentration of KMS respectively. The total colour
difference (ΔE) of potato is found minimum in case of
blanching with 200ppm concentration of potassium meta-
bisulphite (KMS), hence, the concentration found most
effective in preservation of colour. Higher concentrations
show darkening of colour after sometime, one potential reason
could be binding of metal present in potato with residual
sulphite forms black sulphite precipitate.
Table 5: L*, a*, b* value for potato slices blanched with 2%
NaCl and different concentration of KMS
Time
(Hrs.)
Concen
tration
of KMS
(ppm)
L* a* b* ΔE C*
Raw Potato
Slices (Standard)
69.39 -1.40 15.92 -
±15.98
0
0 63.72 -1.32 14.91 ±5.76 ±14.96
200 61.90 -1.31 14.83 ±7.57 ±14.89
400 69.43 -0.88 17.04 ±1.23 ±17.06
600 60.17 -1.42 14.58 ±9.32 ±14.65
1
0 63.09 -1.31 14.61 ±6.43 ±14.67
200 61.86 -1.31 14.71 ±7.63 ±14.76
400 64.00 -0.89 16.92 ±5.50 ±16.94
600 58.57 -1.45 14.40 ±10.92 ±14.47
2
0 62.98 -1.32 14.21 ±6.63 ±14.27
200 61.81 -1.29 14.57 ±7.7 ±14.63
400 62.62 -0.94 16.74 ±6.83 ±16.76
600 57.50 -1.42 14.15 ±12.02 ±14.22
3
0 62.07 -1.29 14.06 ±7.5 ±14.12
200 61.72 -1.26 14.41 ±7.82 ±14.47
400 61.82 -0.97 16.55 ±7.61 ±16.58
600 57.00 -1.47 13.83 ±12.56 ±13.91
4
0 60.06 -1.30 13.35 ±9.68 ±13.41
200 61.68 -1.25 14.29 ±7.88 ±14.34
400 61.39 -0.92 16.31 ±8.02 ±16.33

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Time
(Hrs.)
Concen
tration
of KMS
(ppm)
L* a* b* ΔE C*
600 53.17 -1.52 13.53 ±16.39 ±13.61
5
0 59.57 -1.26 12.77 ±10.31 ±12.83
200 61.63 -1.27 14.11 ±7.96 ±14.16
400 61 -0.94 15.16 ±8.43 ±15.19
600 51 -1.49 13.36 ±18.57 ±13.44
6
0 57.81 -1.21 12.00 ±12.23 ±12.06
200 61.61 -1.31 13.98 ±8.01 ±14.04
400 60.77 -0.97 15.03 ±8.67 ±15.06
600 48.35 -1.53 13.11 ±21.22 ±13.2
24
0 42.33 -0.94 10.97 ±27.51 ±11.01
200 60.98 -1.30 13.88 ±8.65 ±13.94
400 57.33 -1.21 14.34 ±12.16 ±14.39
600 42.76 -1.63 12.53 ±26.84 ±12.63
26
0 39.01 -0.88 10.08 ±30.94 ±10.12
200 60.95 -1.31 13.81 ±8.7 ±13.87
400 57.01 -1.28 14.07 ±12.51 ±14.13
600 42.31 -1.57 12.10 ±27.35 ±12.20
3.6.2 Study of Colour Change of Gelatinized Potato
Mash
Another 5-day study was undertaken to determine the
effectiveness of 200ppm of potassium metabisulphite (KMS)
on gelatinized potato mash prepared under optimized
gelatinization condition (i.e. 10psig for 15minutes). The result
(Table: 6) was found satisfactory as the optimized
concentration of potassium metabisulphite (KMS) was found
to be equally effective in preserving the colour of mashed
potato stored at 40
C for 5 days. The standard in this case was
potato blanched with 2% NaCl and 200ppm KMS and then
mashed in a mixer grinder.
Table 6: L*, a*, b* value for Blanched potato mash
Time
(days)
L* a* b* ΔE C*
Potato
Mash
(Standard)
75.35 -1.27 13.79 - ±15.98
1 75.33 -1.24 13.76 ±0.0469 ±13.81
2 75.31 -1.21 13.74 ±0.0877 ±13.79
3 75.30 -1.23 13.72 ±0.0948 ±13.77
4 75.29 -1.25 13.69 ±0.1183 ±13.75
5 75.27 -1.22 13.65 ±0.1688 ±13.70
3.7 RSM Modeling
3.7.1 % Gelatinized Starch (%GS)
Initially second order model was fitted to response data of %
gelatinized starch data from standard order run 1-9 (Table: 3),
because the optimized gelatinization condition was found in
this factorial design zone. It was found that pressure and
square term of pressure was significant at p= 0.05 for %
gelatinized starch, increase of pressure means also increase in
temperature. So, the significance of pressure also supported by
the theory described earlier Hosney, 1986 [22].
Therefore, model with linear and interactive terms was fitted
to experimental data because of high value of coefficient of
determination (R2
=0.88). Therefore, model with linear and
interactive terms was best fitted to experimental data.
% GS= -70.9344 + 10.5527*P - 0.4735*P2
+ 6.0803T -
0.1947*T2
- 0.0198*P*T............................................... (5)
Where GS is gelatinized starch, P is Pressure (psig), and T is
Time (minutes)
Table 7: Observations of equation (5)
Multiple
R
Multiple
R2
Adjusted
R2
Value
of p for
pressure
Value of p for
square term of
pressure
0.939 0.8817 0.68005 0.03797 0.028012
From the equation (5) the values of % GS can be predicted
and correlation of experimental and predicted data (Fig: 3)
provided an observation that a good relationship exit between
experimental and calculated data means coefficient of
determination value is high (R2
= 0.88).
Experimental value vs. Predicted value
R2
= 0.8819
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35 40
Experimental value of % GS
PredictedValueof%GS
Fig 3: Correlation between experimental and predicted values
of % GS

__________________________________________________________________________________________
3.7.2 Total Colour Difference (ΔE) and Polar
Coordinate Chroma (C*) of Blanched Potato Slices
The RSM modeling was also fitted to response data of total
colour difference (ΔE) and polar coordinate chroma (C*) of
blanched potato slices (table: 5). It was found that time and
square term of time both were significant at p= 0.05 in both of
the modeling. The multiple and adjusted value of coefficient
of determination (R2
) was found to be very good which
indicates that the model with linear and interactive terms was
fitted to experimental data because of high value of coefficient
of determination (R2
).
T.C.D (ΔE) = 7.560223 + 0.085354*t - 0.001625*t2
……... (6)
C* = 14.90249-0.16457*t + 0.00496*t2
…………………... (7)
Where in equation (6) and (7), t is Time (hour(s))
Multiple
R
Multiple
R2
Adjusted
R2
Value of
p for
time
Value of p
for square
term of time
0.99953 0.998307 0.997743 0.000002 0.000066
Multiple
R
Multiple
R2
Adjusted
R2
Value of
p for
time
Value of p
for square
term of
time
0.98349 0.967259 0.956346 0.000091 0.000261
From the equation (6) the values of total colour difference
(ΔE) can be predicted and correlation of experimental and
predicted data (Fig: 4) provided an observation that a strong
relationship exit between experimental and calculated data
means coefficient of determination value is high (R2
= 0.99).
Experimental value Vs. Predicted Value
R2
= 0.9983
7.4
7.6
7.8
8
8.2
8.4
8.6
8.8
7.4 7.6 7.8 8 8.2 8.4 8.6 8.8
ΔE (Experimental)
ΔE(Predictedl)
of T.C.D (ΔE)
From the equation (7) the values of polar coordinate chroma
(C*) can be predicted and plotting of experimental and
predicted data (Fig: 5) provided an observation that a strong
relationship exit between experimental and calculated data
means coefficient of determination value is high (R2
= 0.96).
Experimental value Vs. Predicted value
R2
= 0.9653
13.6
13.8
14
14.2
14.4
14.6
14.8
15
13.8 14 14.2 14.4 14.6 14.8 15
Polar Co-ordinate Chroma (Experimental)
PolarCo-ordinateChroma
(Predicted)
of polar coordinate chroma (C*)
3.8 Regression of Colour Changes of Gelatinized
Potato Mash
A simple regression has been done to obtain the model
equation for dependent variable (total colour difference (ΔE))
and independent variable (time) for gelatinized potato mash
(table: 6). It was found that a good relationship between the
dependent and independent variable exist as the coefficient of
determination value is high (R2
= 0.93). The model equation is
ΔE= 0.02098+ 0.02744*D………………..………………. (8)
Where, D is number of day(s)
Table 10: observation of equation (8)
Multiple R Multiple R2
Adjusted R2
Value of p for
day(s)
0.969435 0.939803 0.919738 0.006385
From the equation (8) the values of total colour difference
(ΔE) can be predicted and correlation of experimental and
predicted data (Fig: 6) provided an observation that a good
relationship exit between experimental and calculated data as
the coefficient of determination value is high (R2
= 0.93).

__________________________________________________________________________________________
Experimental value Vs. Predicted Value
R2
= 0.9395
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
ΔE (Experimental)
ΔE(Predicted)
of T.C.D (ΔE)
CONCLUSION
A study to optimize the best condition of gelatinization was
performed and also the effect of KMS in gelatinization was
studied. The optimized condition was 10 psig for 15 minutes.
During higher temperature and pressure the percentage of
gelatinized starch reduced, one probable reason is at higher
pressure and temperature starch retrogradation may take place.
Another possible reason is excess sulphite from KMS salt
produces sulphur dioxide which under pressure may produce
sulphurus and sulphuric acid and the acids react with the
carbohydrate to produce furfural group which decreases the
final carbohydrate content.
The experimental study with different concentration of KMS
to retain the colour of potato slices was performed and the
results show that 200 ppm was the optimized concentration.
Without KMS and also with higher concentration of KMS the
colour of blanched potato slices hugely. One potential reason
could be binding of iron present in potato with residual
sulphite form black iron sulphite precipitate. The optimized
concentration of KMS i.e. 200ppm also effective to retain the
colour of gelatinized potato mash if the mash stored at 40
C.
Joglekar and May (1987), [23] have suggested for good fit of a
model, regression coefficient (R2
) should be at least 80%, all
the R2
value of different modelling equation in this study are
more 80% (i.e. R2
> 0.80) and also a high similarity was
observed between the predicted and experimental results of
different cases, which reflected the accuracy and applicability
of regression equations or regression model equation of the
study.
ACKNOWLEDGEMENTS
Authors gratefully acknowledge TIFAC-CORE for financial
supports & Techno India for infrastructural facilities.
ABBREVIATIONS
0
C - Degree centigrade
% - Percentage
N – Normality
Psig- Pounds per square inch gage
ΔE – Total colour difference
C* - Polar coordinate chroma
ppm - Parts per million
KMS -Potassium metabisulphite
NaCl – Sodium Chloride
p - Significance level
R2
– Coefficient of determination
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