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Optimization of Ingredients for the Manufacture of Sugar-free Konjac Jelly Drinks by Response Surface Methodology

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Abstract

A central composite rotatable design was applied to evaluate the effect of erythritol-sucralose and citric acid on sensory evaluation of sugar-free konjac jelly drinks. The results showed that sensory scores for color, taste, texture and overall liking ranged from 5.54 to 6.35, 5.54 to 6.82, 5.32 to 6.89 and 5.62 to 6.86, respectively. Response surface analysis revealed that quadratic models for taste, texture and overall liking satisfactorily described sensory acceptance of the products with coefficients of determination or R 2 -values of 0.9178, 0.9298 and 0.9370, respectively. The contour plots showed that all sensory attributes were strongly influenced by erythritol-sucralose. Numerical optimization determined the optimum condition for production of sugar-free konjac jelly drinks based on maximum sensory attributes was achieved at 4% erythritol-sucralose and 0.25% citric acid.
Australian Journal of Basic and Applied Sciences, 4(8): 3546-3552, 2010
ISSN 1991-8178
© 2010, INSInet Publication
Corresponding Author: Adisak Akesowan, Department of Food Science and Technology, School of Science, University
of the Thai Chamber of Commerce, 126/1 Vibhavadi-Rangsit Road,Bangkok, Thailand. Tel: 662-
6976521,
E-mail: adisak_ake@utcc.ac.th
3546
Optimization of Ingredients for the Manufacture of Sugar-free Konjac Jelly Drinks
by Response Surface Methodology
Adisak Akesowan
Department of Food Science and Technology, School of Science,
University of the Thai Chamber of Commerce, Bangkok, Thailand.
Abstract: A central composite rotatable design was applied to evaluate the effect of erythritol-
sucralose and citric acid on sensory evaluation of sugar-free konjac jelly drinks. The results showed
that sensory scores for color, taste, texture and overall liking ranged from 5.54 to 6.35, 5.54 to 6.82,
5.32 to 6.89 and 5.62 to 6.86, respectively. Response surface analysis revealed that quadratic models
for taste, texture and overall liking satisfactorily described sensory acceptance of the products with
coefficients of determination or R2-values of 0.9178, 0.9298 and 0.9370, respectively. The contour
plots showed that all sensory attributes were strongly influenced by erythritol-sucralose. Numerical
optimization determined the optimum condition for production of sugar-free konjac jelly drinks based
on maximum sensory attributes was achieved at 4% erythritol-sucralose and 0.25% citric acid.
Keywords: Low-calorie food, konjac flour, erythritol-sucralose, low-calorie sweetener, response
surface methodology.
INTRODUCTION
With increasing of people who suffer from some diseases such as diabetes, obesity and high blood
pressure, it is evident that one reason comes from individual diet habits and no time for exercise. There is
increasing evidence that consumption of sugar or sweet foods leads to the harmful risk of stated diseases;
consequently, sugar is of interest to replace with low-calorie sweeteners to produce low-sugar or sugar-free
food products (Newsome, 1993). These substances have shown advantages for uses in nutritious products
because they offer less calories, lower health risks and avoid problems with dental decay associated with the
excessive consumption of sucrose (Wallis, 1993; Akesowan, 2010).
A combination of sugar alcohol and intense sweetener has been extensively used in low-calorie food
products, because the individual properties of these low-calorie sweeteners can be combined with advantages,
particular on cost, bulk property and sweetness profile (Verdi and Hood, 1993). An erythritol-sucralose
(98.6:1.4) mixture is currently introduced to a food market as an alternative sugar substitute for consumers who
seek for different sweet taste from aspartame, acesulfame-K or their combinations. Erythritol, a 4-carbon sugar
alcohol (bulking property) with about 60 to 80% of the sweetness of sucrose, provides less than 0.5 kcal/g and
is classified as a non-toxic and non-cariogenic substance which was accepted as food or food additive in many
countries such as USA, Japan, France, Australia and New Zealand (Munro et al., 1998; Wang and Peng, 1998).
Sucralose, an intense sweetener (no bulking property), has shown advantages in relation to the other low-calorie
sweeteners for use in nutritive products because it provides about 600 times of sucrose sweetness with no
aftertaste and tooth decay, good storage stability and low pH and high temperature stability. It was also proved
as safe for human consumption (Wallis, 1993; Mendoca et al., 2001).
Konjac flour or gum, a neutral polysaccharide produced from the tuber of Amorphophallus konjac C. Koch,
consists of D-glucose and D-mannose joined by b-glycosidic linkages or called “glucomanan” (Tye, 1991).
Konjac flour is generally recognized as safe (GRAS), and provides special properties as thickening and gelling
agents. Also, it has been reported to lower serum cholesterol and LDL cholesterol and triacylglycerol (Thomas,
1997). In addition, konjac flour when exposed to water forms a thick viscous solution that enzyme in body
does not digest, resulting in a large soft mass moves through the intestines and may trigger intestinal muscle
contractions. Consequently, konjac flour promotes a larger, bulkier stool that passes through the colon more
easily and requires less pressure and less straining to expel. Several studies have demonstrated that
Aust. J. Basic & Appl. Sci., 4(8): 3546-3552, 2010
3547
glucomannan is an effective treatment for many with chronic constipation (Takigami, 2000).
Recently, the response surface methodology (RSM) is one of the most popular methods which has been
successfully used to account for the possible interaction effects between variables and also overcome the
traditional optimization of the process that known as the one-factor-at-a-time approach (time-consuming
method). It enables the evaluation of the effects of several parameters and their interactions on the response
variables based on a few sets of experiments (Anderson and Whitcomb, 2005).
The objective of this study was to perform a systematic investigation on how different levels of erythritol-
sucralose and citric acid influence on sensory properties of sugar-free konjac jelly drinks by using the RSM
as well as to determine an optimal condition for producing the healthy acceptable product.
MATERIALS AND METHODS
Materials:
Dried roselle calyces (Hibiscus sabdariffa) was purchased from a local supermarket. Konjac flour (Chengdu
Qiteng Trading Co., Ltd) and κ–carrageenan (MSC5744, MSC Ltd., USA) were used. Food grade commercial
low-calorie sweetener, erythritol-sucralose or D–etâ (98.6:1.4) was obtained from U-Sing Co., Ltd., Thailand.
Konjac Jelly Drink Preparation:
Roselle Juice Stock:
A hundred gram of dried roselle calyces was washed and soaked in water for 15 min. The rehydrated
roselle was added in 1000g boiling water and kept boiling for 30 min. After cooling, roselle liquid was poured
through a cheesecloth into sterilized glass bottles and stored in a refrigerator (10 ± 2°C) prior to processing.
Sugar-free Konjac Jelly Drink:
A 20% roselle juice was prepared by mixing roselle juice stock with distilled water at a ratio of 20:80
(v/v). A konjac flour and κ–carrageenan (3:1) mixture was gradually added into 20% roselle juice before
heating at 90 ± 2°C for 15 min in a water bath. Erythritol-sucralose and citric acid were added and keep
heating for 5 min. The hot mixture was filled into cups (3 cm diameter x 3 cm height) and let them cool down
to room temperature (30 ± 2°C), the samples were stored at 4 ± 2°C prior to analysis.
Experimental design:
Two independent variables; erythritol-sucralose (%) and citric acid (%) were investigated for their
influences on sensory properties of sugar-free konjac jelly drinks. A central composite rotatable design (CCRD)
for a two-variable, five combinations coded -1.41, -1, 0, 1, 1.41 was employed to study the combined effect
of these independent variables. Experimental design and actual values for sugar-free konjac jelly drink
production are shown in Table 1. This design required eleven sets of randomized experiments, which included
four factorial points, three central points and four extra axial points. The model proposed for the response is
Y = b0 + b1X1 + b2X2 + b
11 + b
22 + b
12 X1X2 (1)
2
1
X
2
2
X
where Y is the response calculated by the model; X1 and X2 are the coded erythritol-sucralose and citric acid,
respectively, and b1 and b2 are linear, b11 and b12 are quadratic, and b12 is interaction coefficient, respectively.
Sensory Evaluation:
Sensory evaluation was conducted by forty-eight panelists who were experienced in sensory evaluation of
foods, but received no specific training relevant to these products. Sensory color, taste, texture and overall
liking were evaluated by using a 9-point hedonic scale test (1 = extremely dislike, 9 = extremely like). All
testing sessions were held in a sensory evaluation laboratory with partitioned booth. Unsalted cracker, apple
juice and distilled water were provided to rinse the palate between samples (Lawless and Heymann, 1998).
Statistical Analysis
The production of sugar-free konjac jelly drink was carried out in triplicate. The observed response was
subjected to analyze for analysis of variance (ANOVA) and regression using the Design-Exper® version
8.0.2.0 software (State-Ease Inc., Minneapolis, MN) in order to visualize the relationship between the response
and experimental levels of each factor and to deduce the optimum condition (Anderson and Whitcomb, 2005).
Aust. J. Basic & Appl. Sci., 4(8): 3546-3552, 2010
3548
RESULTS AND DISCUSSION
The experimental sensory responses in a function of erythritol-sucralose concentration (X1) and citric acid
concentration (X2) for producing sugar-free konjac jelly drinks are summarized in Table 2 with coded variable
levels. The scores of color, taste, texture and overall liking were within the ranges of 5.54–6.35, 5.54–6.82,
5.32–6.89 and 5.62–6.86, respectively. The effect of different variables on these attributes represented
statistically by the regression analysis of the data is shown in Table 3. The results indicated that the models
for all sensory attributes, except for color were highly adequate with their satisfactory levels of coefficient of
determination or R2 from 0.9178 to 0.9370 and all models were significant at p < 0.05. It has been suggested
that the model with R2 greater than 0.8 indicates a good fit (Joglekar and May, 1987).
Sensory Evaluation:
The formulation that showed maximum scores for taste (6.82) and texture (6.89) contained 4% erythritol-
sucralose and 0.25% citric acid, while the product formulated with 4.41% erythritol-sucralose and 0.15% citric
acid showed the greatest overall liking score (6.86), as evidence in Table 2. This indicated that most panelists
preferred high sweet and sour taste of sugar-free konjac jelly drink. The RSM was used to evaluate the effect
of erythritol-sucralose (X1) and citric acid (X2) on sensory perception of the product, and then to build a model
that describes the behavior of taste, texture and overall liking to optimize the process by finding the best
concentration of erythritol-sucralose and citric acid that maximize the sensory attributes. The statistical analysis
presented in Table 3 shows regression coefficients for taste, texture and overall liking in terms of coded
variables. In this case, non-significant terms can be removed to make the regression equations simple.
Therefore, the model equation for each sensory attribute is in the form:
Taste = 7.66 – 1.57 X1 – 4.59 X2 + 0.31 + 16.25 (2 )
2
1
X2
2
X
Texture = 3.33 + 1.66 X1 – 0.25 X2 – 0.23 (3 )
2
1
X
Overall liking = 6.81 – 0.85 X1 – 3.73 X2 + 0.18 (4 )
2
1
X
where X1 = erythritol-sucralose (%) and X2 = citric acid (%)
In general, proceeding with exploration and optimization using a fitted response surface may produce
misleading results unless the model exhibits an adequate fit. This is essential to check the model adequacy (Liu
et al., 2008). Analysis of variance (ANOVA) gives the validity of the model and can explain whether the
model adequately fits the variation observed in sensory evaluation at the designed ingredient level. When
considering ANOVA for the model predicted for this experiment (Table 4), it was observed that the calculated
F-values for models of taste, texture and overall liking were significant at 5% level (p < 0.05) and the F-test
for the lack of fit were not significant (p > 0.05), then these models were reliable. The low probability values,
i.e. P = 0.0096 for taste was also supportive of the significance of the models. The goodness of the fitted
model was checked by the coefficient of determination (R2). From Table 3, the coefficient of determination
for taste (R2 = 0.9178), texture (R2 = 0.9298) and overall liking (R2 = 0.9370), indicated that 91.78% of taste,
92.98% of texture and 93.70% of overall liking could be explained by the fitted model. At the same time, the
coefficients of variation of 3.11% for taste, 2.68% for texture and 2.28% for overall liking were relatively low.
This indicated that overall liking had better precision and reliability of experiments as compared with taste and
texture perception. Therefore, these models adequately represented the real relationship between the parameters
chosen. The predicted models seem to be represented reasonably the values observed. In fact, it was confirmed
by a low F-test value for color response (Table 4), which indicated that the model was not significant (p >
0.05).
Response Surface and Contour Plotting:
With these statistical models, eq. 2–4, the three-dimensional responses and two-dimensional contour plots
(Fig. 1) are illustrated for representing the influence of erythritol-sucralose and citric acid on taste, texture and
overall liking of sugar-free konjac jelly drinks. The response surface plot for taste shown in Fig.1a exhibits
an increase of both erythritol-sucralose and citric acid increased taste scores of the products, indicating that
sweet and sour taste would be the preferable taste of this product. As shown in Fig.1b, the control plot,
represented an infinite number of combinations of these two variables, displayed a significantly effect on taste
scores. The taste was mostly influenced by erythritol-sucralose. In fact, the increase of erythritol-sucralose
strongly increased taste score of the product while increasing citric acid promoted the increased level of taste
score where the concentration of erythritol-sucralose (< 3.45%) was used.
Aust. J. Basic & Appl. Sci., 4(8): 3546-3552, 2010
3549
When considering the response and contour plots for texture in Fig.1c-d, it can be seen that texture score
of sugar-free konjac jelly drink was increased with increasing of both erythritol-sucralose and citric acid. The
contour shown in Fig.1d shows that erythritol-sucralose was the greatest effect on texture score. On the other
hand, effect of erythritol-sucralose and citric acid on texture of the products was significant at higher level of
erythritol-sucralose used (> 2.75%).
The response surface plot for overall liking (Fig.1e) demonstrated a same trend as the surface plots of taste
and texture, showing a higher level of erythritol-sucralose and citric acid led to a higher score of overall liking.
The contour plot (Fig.1f) displayed that an increase in overall liking was strongly influenced by erythritol-
sucralose, especially on high concentration. The effect of two variables was significant at the low concentration
of erythritol-sucralose used (< 2.90%).
Table 1: Independent variables and their coded and actual values used for analysis
Independent variables Unit Symbol Coded levels
----------------------------------------------------------------------------------------------------
-1.41 -1 0 1 1.41
Erythritol–sucralose % X11.59 2344.41
Citric acid % X20.01 0.05 0.15 0.25 0.29
Table 2: Experimental combinations and data under various conditions of sugar-free konjac jelly drinks
Experimental no. Coded variables Sensory responses
------------------------------------- --------------------------------------------------------------------------------------------
X1X2Color Taste Texture Overall liking
1 -1 -1 5.98 5.74 5.98 5.85
2 +1 -1 6.28 6.15 6.38 6.15
3 -1 +1 5.59 6.16 6.15 6.12
4 +1 +1 5.54 6.82 6.89 6.78
5 -1.41 0 6.22 5.54 5.32 5.62
6 +1.41 0 6.20 6.78 6.72 6.86
7 0 -1.41 5.85 5.65 6.12 5.85
8 0 +1.41 5.84 6.10 6.82 6.33
9 0 0 6.35 5.72 6.63 5.98
10 0 0 6.06 5.65 6.56 5.88
11 0 0 6.15 5.58 6.42 5.90
Variable: X1 = erythritol-sucralose (%) and X2 = citric acid (%).
Table 3: Regression coefficients for different attributes of sugar-free konjac jelly drinks
Factor Sensory attributes
----------------------------------------------------------------------------------------------------------------------------------------
Color Taste Texture Overall liking
Intercept 5.1387 7.6593 3.3314 6.8114
Erythritol-sucralose (X1) 0.3590 -1.5708** 1.6550** -0.8458***
Citric acid (X2) 7.6698 -4.5920*-0.2501*-3.7265**
-0.0333 0.3050*-0.2321*0.1750*
2
1
X
-21.5833 16.2500** -0.7083 10.0000
2
2
X
X1X2-0.8750 0.6250 0.8500 0.9000
R20.6311 0.9178 0.9298 0.9370
Coefficient of variation 4.71 3.11 2.68 2.28
***Significant at p < 0.001, **Significant at p < 0.01, *Significant at p < 0.05.
Table 4: Analysis of variance for the second-order regression models on sensory evaluation
Response Source DF SS MS F P
Color Regression 5 0.47 0.094 1.71 0.285
Residual 5 0.27 0.055
Lack of fit 3 0.23 0.077 3.48 0.2311
Pure error 2 0.044 0.022
Total 10 0.74
Taste Regression 5 1.94 0.39 11.17 0.0096
Residual 5 0.17 0.035
Lack of fit 3 0.16 0.055 11.17 0.0833
Pure error 2 9.80E-03 4.90E-03
Total 10 2.12
Aust. J. Basic & Appl. Sci., 4(8): 3546-3552, 2010
3550
Table 4: Continue
Texture Regression 5 1.92 0.38 13.24 0.0066
Residual 5 0.15 0.029
Lack of fit 3 0.12 0.041 3.56 0.2268
Pure error 2 0.023 0.011
Total 10 2.07
Overall liking Regression 5 1.45 0.29 14.87 0.0051
Residual 5 0.098 0.02
Lack of fit 3 0.092 0.031 10.96 0.0848
Pure error 2 5.60E-03 2.80E-03
Total 10 1.55
DF-degree of freedom; SS-sum of square; MS-mean square; F-statistics test to determine significance; P-probability value.
Table 5: Criteria and outputs for numerical optimization of sugar-free konjac jelly drinks
Criteria Goal Limit Outputs
----------------------------------------------------------------------
123
Erythritol-sucralose (%) In the range 2 – 4 4.00 3.98 3.96
Citric acid (%) In the range 0.05–0.25 0.25 0.25 0.25
Taste Maximize 5.54–6.82 6.75 6.73 6.71
Texture Maximize 5.32–6.89 6.98 6.98 6.98
Overall liking Maximize 5.62–6.86 6.82 6.81 6.79
Desirability 0.971 0.963 0.953
Based on the results showed in Fig.1b, 1d and 1f, one can infer that the high level of erythritol-sucralose
and citric acid was associated with an acceptable texture of sugar-free konjac jelly drinks. It can be proposed
that a high amount of erythritol-sucralose may disturb the gel formation between konjac flour and
κ–carrageenan, whereas an acid condition by a high level of citric acid used also affected the
konjac–κ–carrageenan gel system (Takigami, 2000), resulting in a soft gel texture that can be easily sucked
by a straw, which was the desirable and dominant characteristic of this product. Some panelists have suggested
that the products should be increased with an amount of erythritol-sucralose used, because the products seem
to be less in sweet taste. This may be due to the sweetness of erythritol being about 60 to 80% compared to
that of sucrose and different sweetness profiles of both erythritol and sucralose in relation to that of sucrose
(Goossens and Röper, 1994). In addition, overall liking of the product would be influenced by both taste and
texture perception.
Optimization of the Experimental Conditions:
In order to arrive at the optimum condition for producing sugar-free konjac jelly drink made with
erythritol-sucralose and citric acid. Design-Expertâ version 8.0.2.0 software was used while the desired goals
for each variable and response were chosen as summarized in Table 5. Numerical optimization was carried
out for this study. Table 5 shows the software-generated optimum condition for independent variables with
predicted values of responses, which were 4% erythritol-sucralose and 0.25% citric acid for achieving the
highest scores of taste = 6.75, texture = 6.98 and overall liking = 6.82.
Conclusion:
The RSM was successfully used to optimize the ingredients for producing sugar-free konjac jelly drinks.
Two parameters, erythritol-sucralose and citric acid, tested by CCRD, showed significant linear and quadratic
effects on taste, texture and overall liking of the products. The mathematical models obtained can predict
sensory scores at different levels of erythritol-sucralose and citric acid and enabled to select level of the
variables to maximize the product acceptance. The optimal predicted sensory scores (taste = 6.75, texture =
6.98 and overall liking = 6.82) was obtained under the optimum concentration of erythritol-sucralose and citric
acid at 4 and 0.25%, respectively.
ACKNOWLEDGEMENTS
The author wish to acknowledge the financial support from the University of the Thai Chamber of
Commerce and panelists for their time.
Aust. J. Basic & Appl. Sci., 4(8): 3546-3552, 2010
3551
(A) (B)
© (D)
(E) (F)
Surface plot Contour plot
Fig. 1: Surface and contour plots for sensory attributes of sugar-free konjac jelly drinks:
(a, b) taste; (c, d) texture and (e, f) overall liking
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Book
RSM Simplified keeps formulas to a minimum and makes liberal use of figures, charts, graphs and checklists. It offers many relevant examples, with amusing sidebars and do-it-yourself exercises that will lead readers to the peak potential for their product quality and process efficiency. The authors, Mark J. Anderson and Patrick J. Whitcomb, are principals of Stat-Ease, a provider of DOE training, consulting, and software. They both are professional chemical engineers. Anderson has more of a business background while Whitcomb specializes in statistics. Incorporated into this book is the more advanced Design-Expert, version 7 software for Windows, with a 180-day trial, so the reader can do the complex statistical computations, generate the necessary graphics (2D and 3D maps) and perform the numerical optimization.