Scholarly article on topic 'Effect of Ingredients on Texture Profile of Fermented Food, Idli'

Effect of Ingredients on Texture Profile of Fermented Food, Idli Academic research paper on "Agriculture, forestry, and fisheries"

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{"Fermented food" / "Product optimization" / Idli / "Texture Profile Analysis (TPA)" / "Response Surface Methodology (RSM)" / "Central Composite Rotatable Design (CCRD)" / "Texture analyser"}

Abstract of research paper on Agriculture, forestry, and fisheries, author of scientific article — Manoharan Durgadevi, Prathapkumar Halady Shetty

Abstract Idli is one of the most popular fermented breakfast snack consumed in India and Sri Lanka with immense commercial prospects. However scientific optimization of the process is the basic necessity for commercialization of any product including the fermented foods. Present study was aimed to optimize the ratios of rice to black gram dhal and fermentation time for idli. Instrumental Texture Profile Analysis was conducted to optimize the textural properties of idli. The maximum and minimum ranges for the independent variables were selected using preliminary trial and a second order polynomial model was fitted with the response variables. Various TPA parameters were analysed by RSM to obtain a predicted optimized ratio of rice and black gram dhal of 3:1.575 w/w with 14 hours as fermentation time. The optimum results were validated by performing the experiment by comparing the observed and the predicted values. The predicted values were insignificant with observed values indicating the appropriateness of the model developed. Based on the results, it was concluded that at an optimum ratio of rice and black gram dhal (3: 1.575 w/w), will give product with desirable texture properties. These results will have direct implications in the commercialisation of the product.

Academic research paper on topic "Effect of Ingredients on Texture Profile of Fermented Food, Idli"

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APCBEE Procedia 2 (2012) 190 - 198

ICBFS 2012: April 7-8, 2012, Bangkok, Thailand

Effect of Ingredients on Texture Profile of Fermented Food, Idli

Manoharan Durgadevi and Prathapkumar Halady Shetty*

Department of Food Science and Technology, Pondicherry University, Puducherry 605014, India.

Abstract

Idli is one of the most popular fermented breakfast snack consumed in India and Sri Lanka with immense commercial prospects. However scientific optimization of the process is the basic necessity for commercialization of any product including the fermented foods. Present study was aimed to optimize the ratios of rice to black gram dhal and fermentation time for idli. Instrumental Texture Profile Analysis was conducted to optimize the textural properties of idli. The maximum and minimum ranges for the independent variables were selected using preliminary trial and a second order polynomial model was fitted with the response variables. Various TPA parameters were analysed by RSM to obtain a predicted optimized ratio of rice and black gram dhal of 3:1.575 w/w with 14 hours as fermentation time. The optimum results were validated by performing the experiment by comparing the observed and the predicted values. The predicted values were insignificant with observed values indicating the appropriateness of the model developed. Based on the results, it was concluded that at an optimum ratio of rice and black gram dhal (3: 1.575 w/w), will give product with desirable texture properties. These results will have direct implications in the commercialisation of the product.

© 2012 Published by E lsevier B.V. Se lection and/orpeerreview under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society

Keywords: Fermented food, Product optimization, Idli, Texture Profile Analysis (TPA), Response Surface Methodology (RSM), Central Composite Rotatable Design (CCRD), Texture analyser

1. Introduction

Indigenous fermented foods have been prepared and consumed for thousands of years, and are strongly linked to culture and tradition. The fermented foods are better in terms of nutrition and easy for digestion than the normal cooked foods. Fermented foods are part of the day to day diet in all parts of the world. Idli is one

Corresponding author. Tel.:+91 9442293718; fax: +91 4132656743. E-mail address: shetty.fst@pondiuni.edu.in.

2212-6708 © 2012 Published by Elsevier B.V. Selection and/or peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi: 10.1016/j.apcbee.2012.06.034

such fermented food widely consumed in India and Srilanka. Idli is made from rice and dehusked blackgram dhal, soaked, ground, fermented and steamed. Apart from its unique texture properties, idli makes an important contribution to the diet as a source of protein, calories and vitamins, especially B-complex vitamins, compared to the raw unfermented ingredients (1). Black gram, the leguminous component of idli batter, serves not only as effective substrate but also provides the maximum number of micro-organisms for fermentation (2). Fermentation also improves the protein efficiency ratio (PER) and a significant increase in predicted biological value of idli over the unfermented mixture (3,4). Fermented foods in general have immense scope for commercialisation as foods with improved nutritional value as well as functional foods. Current study is undertaken to optimise the process of idli which will help the industrial production of idli with the desired quality. The main objectives of this study were to explore the effect of different ratios of rice to black gram dhal and fermentation time on the texture of idli, analysing the instrumental texture profile (TPA) parameters as a function of raw material composition and fermentation time and to find the optimum levels to maximise the desirable textural properties of idli using RSM. Several researchers have used RSM successfully to optimize the conditions for other traditional Indian food products like Boondi (5), tandoori roti, puri and parotta (6,7) .

2. Materials and methods

2.1. Materials

The commonly used local variety of parboiled rice namely IR 20 idli rice (Starch-79.5 %, Amylose- 32 %) was procured from local market and black gram variety Aduthurai 3 (ADT3) which has 24.16 % protein content was procured from Tamil Nadu Rice Research Institute (TRRI), Aduthurai Tamilnadu, India. They were cleaned and stored at refrigerated conditions until use.

2.2. Preparation of idli

Before framing central composite rotatable design (CCRD), trails were conducted to choose the ratios of rice to black gram dhal. The trails were done using rice to black gram dhal ratios as 3:0.5, 3:1, 3:1.5, 3:2, 3:2.5 and 3:3 respectively where rice ratios were kept constant and the dhal ratios varied. The fermentation time varied between 10 to 14h. In the trial, idli made from the ratio 3:1 and 3:1.5 with a fermentation time between 12 to 14 h gave better results based on the physical parameters. Based on this, the maximum and minimum values for the independent variables were chosen to frame the model. The rice and black gram dhal were mixed at different ratios as per the CCRD. The rice and dhal were soaked for 4 h and ground separately to a coarse consistency and mixed together with salt. The batter was left overnight (time based on the developed design) for fermentation. The fermented batter was mixed thoroughly to expel the gas formed due to the release of carbon-dioxide .The batter was poured in idli mould, and steamed in the idli steamer for 15 minutes. The idli were brought to room temperature and then used for instrumental texture profile and sensory analysis.

3. Experimental design

3.1. Response surface Methodology

RSM is a collection of statistical and mathematical techniques useful for developing, improving, and optimizing processes in which a response of interest is influenced by several variables and the objective is to

optimize this response. RSM has important application in the development and formulation of new products, as well as in the improvement of existing product. It defines the effect of the independent variables, alone or in combination, on the responses. In addition to analysing the effects of the independent variables, it provides a mathematical model, which describes the relationships between the independent and response variables (8). In the study, RSM as described by Box and Wilson (9) was conducted to determine the optimum conditions of two independent variables (rice to black gram dhal ratio and fermentation time) on the TPA and colour attributes of idli. A CCRD was constructed using software package Statistica (1999) from StatSoft, OK, USA. Maximum and minimum predictor values were chosen after carrying out preliminary trails. Five levels of each predictor variable were incorporated into the developed design. RSM reduces the number of experimental trials needed to evaluate multiple parameters and their interactions.

3.2. Optimization of idli

The procedure was based on the hypothesis that quality attributes of idli were functionally related to rice to black gram dhal ratio and fermentation time, and attempts were made to fit multiple regression equations describing the responses. Two coded independent variables in the process were rice to black gram dhal ratio (Xi) and fermentation time (X2). Five levels of each of the independent variable were chosen for the study; thus, there were 13 combinations, including the replicates of the centre point that were performed in random order, based on an experimental CCRD for two factors (Table 1 and 2). The dependent variables were hardness, adhesiveness, springiness, cohesiveness, chewiness and resilience and colour attributes.

3.3. Instrumental Colour Measurement

Colour of the idli is one of the most important parameter for the acceptability of the product. The colour parameters of idli were measured using a Hunter Lab colour flex model A60-1012-312 (Hunter Associates laboratory, Reston,VA) . The chroma and Hue values were calculated by the formula Eqn.2 and Eqn. 3.

Chroma — Va2 + b2 (2)

where 'a' indicated Red-Green colour components, while 'b' indicates yellow to blue colour components (10).

3.4. Texture profile analysis (TPA)

The TPA test consists of compressing a bite-size piece of idli two times in a reciprocating motion that imitates the action of the jaw. The texture of each idli was analysed using P/75mm compression platen in Texture Analyser (Stable Micro Systems, Surrey, UK). The idli was cooled to room temperature and was cut into an inch cube using an inch cubic mould. The extra top and bottom layers were sliced off to make the idli fit to the mould. The cut piece was placed on the heavy duty platform and the test speed was set to 5mm/sec and the probe compressed a distance of 10 mm of the cut idli to get the TPA of the idli. Based on the force deformation curves, several parameters like adhesiveness, springiness, cohesiveness, chewiness and resilience can be calculated by the in built software.

3.5. Statistical Analysis

The independent variables and dependent variables (responses) were fit to the second-order polynomial function and examined for the goodness of fit. The R2 or coefficient of determination is the ratio of explained

variation to the total variation and is a measure of the degree of fit (11). All experimental designs and statistical data were analysed and response surfaces, ANOVA, regression analysis were reported using Statistica (StatSoft, OK, USA) statistical software.

Fig.1 Response surface graphs showing relation between ratios of rice to black gram dhal and fermentation time on texture parameters of idli A) Hardness, B) Adhesiveness, C) Springiness, D) Cohesiveness, E) Chewiness, F) Resilience.

4. Results and discussion

4.1. Response surface Contours

Several parameters namely raw material variety, quality, their proximate composition, raw material composition, particle size, temperature etc., affect the texture of idli but still, the texture of idli is very unique from the consumer point of view. Among all the parameters mentioned, fermentation time is one of the key factors which can affect the texture very significantly because of the formation of air pockets and leaving action. The texture of the cooked idli is a subject of interest, to judge and optimize the production process of good textured idli with the selection of the ingredients and the process. The fermentation periods are slightly different for idli making owing to the difference in raw materials, composition, process and region (12). The colour of the idli showed variation based on the ratio of rice and black gram dhal used.

Table l.Experimental design: CCRD with actual levels of independent variables for colour attributes

Experimental design points Rice : Dhal Ratio (w/w) Fermentation time (h) Instrumental colour parameters

Actual X1 Actual X2 L* a* b* Chroma Hue angle (°)

1 3 : 0.72 10.58 74.03 +0.07 -0.44+0.021 11.52+0.064 11.56 -87.72

2 3 : 0.72 13.42 74.13 +0.07 -0.57+0.007 10.60+0.035 10.59 -86.92

3 3 : 1.78 10.58 75.76 +0.11 -0.25+0.028 12.21+0.085 12.15 -88.92

4 3 : 1.78 13.42 73.99 +0.06 -0.24+0.021 13.57+0.007 13.56 -89.03

5 3 : 0.50 12.00 75.57 +0.07 -0.76+0.035 10.01+0.36 9.936 -85.79

6 3 : 2.00 12.00 75.78 +0.03 -0.02+0.070 15.97+0.085 16.03 -89.89

7 3 : 1.25 10.00 73.40 +0.11 -0.43+0.014 13.09+0.177 12.96 -88.14

8 3 : 1.25 14.00 74.32 +0.51 -0.13+0.014 11.88+0.205 11.74 -89.14

9 3 : 1.25 12.00 74.35 +0.11 -0.40+0.007 10.56+0.163 10.44 -87.81

10* 3 : 1.25 12.00 74.36 +0.05 -0.43+0.028 10.61+0.361 10.35 -87.73

*Centre point replicated 3 times

The L* value (Table 1) which correspond to lightness ranged from 73.40 to 75.99 indicating the difference in the proportion of black gram dhal used. The positive values of b* indicates yellowness in the idli, which may be due to the use of black gram with husk for soaking. The chroma values are closer to the b* values. The hue angle value corresponds to whether the object is red, orange, yellow, green, blue, or violet (10). The negative values of hue angle shows that the product deviates from the colour adding positive factor to the

current study because lightness in the colour of the idli is an important factor in the view of customer perception. The intensity of chroma is low for the idli made with the ratio of 3:0.5 and is higher for the idli made from the ratio 3:2 showing that the ratio of rice and dhal used for idli making has an impact on the intense of chroma of the idli.

Table 2. Experimental design: CCRD with coded and actual levels of independent variables for TPA Experimenta Rice : Dhal Fermentation Dependent variables

l design Ratio time

point Actual Xi (w/w) Code d X1 Actua l X2 (h) Code d X2 Hardnes s (N) Adhesive -ness (N s) Springi -ness Cohesive -ness Chew-iness Resilienc e Sensor y scores

1 3 : 0.7 2 -1 10.58 -1 23.736 -0.05127 0.926 0.876 1963.61 4 0.595 5

2 3 : 0.72 -1 13.42 1 20.587 -0.03377 0.960 0.819 1650.89 8 0.562 5

3 3 : 1.7 8 1 10.58 -1 44.199 -0.02845 0.809 0.643 2344.08 1 0.340 7

4 3 : 1.78 1 13.42 1 36.575 -0.00051 0.847 0.674 2127.97 3 0.404 7

5 3 : 0.50 1.414 12.00 0 20.669 -0.00514 0.854 0.912 1845.66 4 0.654 4

6 3 : 2.0 0 1.414 12.00 0 32.470 -0.02903 0.965 0.825 2333.37 9 0.511 7

7 3 : 1.2 5 0 10.00 1.414 35.365 -0.00857 0.733 0.526 1389.17 2 0.285 6

8 3 : 1.2 5 0 14.00 1.414 24.128 -0.00086 0.916 0.755 1701.18 9 0.483 7

9 3 : 1.2 5 0 12.00 0 30.858 -0.00624 0.928 0.876 2557.13 5 0.579 8

10* 3 : 1.25 0 12.00 0 30.724 -0.00570 0.913 0.885 2532.79 5 0.574 7

*Centre point replicated 3 times

4.2. Texture parameters

Hardness of idli is indicated by the maximum force required to compress the idli and usually represented by the first peak in the graph. The hardness of the idli (Table 2) varies between a minimum force of 20.58 N to a maximum force of 44.19 N i.e., the minimum force was required to compress idli of ratio 3:0.72 at 13.42 h fermentation time and the maximum force for the ratio 3:1.78 at 10.58 h of fermentation time. This variation in the force is due to the variation in the ratio of the ingredients and fermentation time of the batter.

Higher the force shows that harder is the idli. ANOVA results indicated that the ratio of rice and black gram dhal used for idli making (in the linear effect) is significant (p< 0.05) to the hardness of the idli. The coefficient of regression is given in Table 3. The goodness of fit was high showing high R2 value (0.942). The negative peak in the graph is taken as the adhesiveness. The adhesiveness of the idli varies between -0.00051N s to -0.05127 N s. If the product is sticky, the adhesiveness will be higher. Ghasemi et al (13) reported that the adhesiveness may be due to the better gelatinisation and more fluidity of rice starch structure in the cooked samples. In the current study since the batter was coarse ground and cooking time was constant the adhesiveness must be due to the ratio of rice and dhal and the quality of the ingredient. The minimum adhesiveness is obtained for the idli made of ratio 3:0.5 at 12 h fermentation time and the maximum adhesiveness is obtained for the ratio 3:0.72 at 10.58 h fermentation time. The springiness of idli depends on the quantity of the dhal used because the soft spongy texture observed in the leavened steamed idli made out of black gram is due to presence of two components, namely surface active protein (globulin) and a polysaccharide (arabinogalactan) in black gram (14-17). The specialty of black gram in idli preparation is due to the mucilaginous property which helps in the retention of carbon-dioxide evolved during fermentation (18). In the current study the springiness varied from 0.733 to 0.965. The maximum springiness is obtained for the ratio 3:2 at 12 h fermentation time. Hence the result reveals that the quantity of black gram dhal used has a major role in the springiness of the idli. From Ttable 3 it is clear that the independent variables in the linear effect showed a significant influence on the springiness of the idli and the model showed high goodness of fit (R2 = 0.90947) . Cohesiveness is defined as the ratio of the positive force area during the second compression to that during the first compression. Cohesiveness is minimum (0.526) for the ratio 3:1.25 at 10 h fermentation time and maximum (0.912) for the ratio 3:0.5 at 12 h fermentation time. Both the independent variables namely rice to black gram dhal ratio in linear effect and fermentation time in quadratic effect is significant at 5 % level on the cohesiveness of the idli. Chewiness is defined as the product of (hardness x cohesiveness x springiness ) and is therefore influenced by the change of any one of these parameters. Lower the chewiness softer is the idli. The chewiness of the idli varied between 1389.172 for the ratio 3:1.25 at10 h fermentation time to 2557.135 for the ratio 3:1.25 at 12 h fermentation time. It is proved by the ANOVA table that the ratio of rice to black gram dhal in linear effect and fermentation time in quadratic effect also have significant impact (p < 0.05) on the chewiness of the idli. As hardness, springiness and cohesiveness show significant influence because of the independent variable hence the chewiness of the idli will also be affected by the both independent and dependent variables. The chewiness of the idli varied for the same ratio of idli with difference in fermentation time which relates the decrease in cohesiveness with further increase in fermentation time. Resilience is a measurement of how the sample recovers from deformation both in terms of speed and forces derived. The resilience varies between 0.285 for the ratio 3:1.25 at 10 h fermentation time to 0.654 for the ratio3:0.50 at 12 h fermentation time. Lower resilience value shows that the product can recover faster from deformation proving the firmness of the product. From the ANOVA table it is evident that the resilience of the idli is influenced significantly by rice to black gram dhal ratio in linear effect and by fermentation time either in linear or quadratic effect. The closer the value of R2 approaches unity, the better the empirical model fit the actual data (19). As the R2 value for resilience (0.9323) was closer to unity and the result of resilience fit to the actual data. The response surface graphs for texture parameters are shown in Figure 1(A to F).

4.3. Simultaneous optimization

Simultaneous optimization was performed on the TPA parameters like hardness, adhesiveness, springiness, cohesiveness, chewiness and resilience by imposing desirability constraints. In case of springiness, the softer idli shows high springiness. Hence the software take into account of the values of independent and dependent

values and finally gives a maximum desirable score and the condition at which the maximum score can be obtained with some constraints by assigning maximal desirability score as one and minimal desirability score as zero.

Table 3.Regression co-efficient for dependent TPA parameters

Regression Co-efficient Independent _

variables Hardness Springiness Cohesiveness Chewiness Resilience Sensory Score

Mean/Interaction 34.389 -2.254 -5.876 -23868.30 -4.580 -37.92

1. Rice : Dhal ratio (L) 31.131 -0.182 * -0.527 * 661.94 * -0.605 *

* 10.83*

Rice : Dhal ratio (Q) 1.981 -0.001 -0.048 -378.64 -0.003 -3.55*

2. Fermentation time (L) -3.516 * 0.524 * 1.161 4241.93 0.902 * 6.12

Fermentation time (Q) 0.147 -0.020 -0.049 * -178.51 -0.038 * -0.25

1L by 2L -1.643 0.008 0.041 63.76 0.036 0.00

R2 0.942 0.908 0.886 0.85 0.931 0.94622

L - Linear effect; Q - Quadratic effect; *P < 0.05

Table 4. Simultaneous optimization of process parameters by desirability approach

Independent parameters Dependent variables Overall

Rice : dhal Fermentation TPA parameters and Constraints Predicted Desirability ratio (w/w) time (h) L* values Imposed Values score

Hardness Minimize 19.34

3 : 1.575 13.90 Adhesiveness Minimize -0.03

Springiness Maximize 0.95

Cohesiveness Minimize 0.77 0.8279

Chewiness Minimize 1299.7

Resilience Maximize 0.555

L* (lightness) Maximize 75.16

Sensory score Maximize 7.78

Table 4 shows the constraints imposed for good textured idli with the desirable value for both independent and dependant variables. The maximum desirable score that can be achieved with the desirable value will be 0.8279. On the basis of these calculations good textured idli could be made when 3:1.575 (w/w) ratio of rice to black gram dhal respectively is fermented for 14 h. The optimum results were validated by performing the experiment at the optimized ratio and fermentation time by comparing the observed and the predicted values.

5. Conclusion

Current study showed that RSM based TPA for idli was found to be an effective tool to predict the relationship between the rice to black gram dhal ratio and fermentation time on the textural properties namely hardness, adhesiveness, springiness, cohesiveness, chewiness and resilience. RSM demonstrated the effect of individual factor on the results of multi-factor experiment and sought the optimum condition for each variable. From the study it was concluded that the optimum ratio of rice to black gram dhal is 3:1.575 with an optimum fermentation time of 14 h and a desirable value of 0.8279 will be obtained for the product. The results were validated by preparing idli at the optimized condition. The results prove the designed model to be valid. The finding of this study will support the manufacturers at industrial level to produce idli with the desired textural property with repeatability and uniform quality fulfilling customer expectation.

Acknowledgement

Author is grateful to Pondicherry University for providing necessary facility to carry out the work and to University Grants Commission for providing fellowship to the first author.

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