DEVELOPMENT AND CHARACTERIZATION OF MAIZE-FINGER MILLET BASED PROTEIN ENRICHED EXTRUDED PRODUCTS

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Date
2019
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Indira Gandhi Krishi Vishwavidyalaya, Raipur
Abstract
Processed foods have become popular since past two to three decades worldwide and continue to remain popular due to several reasons such as longer shelf-life, convenient in handling and packaging, nutritional and health benefits, changing food habits of teenagers and children, varying choice of individuals, tight schedule of working hours etc. Most of the snack foods are ready-to-eat or ready-to-cook processed foods prepared either from single commodity or combining two or more commodities. There are several ways and means to prepare snack foods. Extrusion cooking is one of the advanced technologies commercialized and being used in the food process industries for the preparation of range of snack or extruded foods. It has the ability to produce products with multi ingredients or fortification of nutrients easily and accurately. With the increasing demand of snack foods in the market, extruded foods find great opportunity. In the preparation of extruded foods, the choice of ingredients or the composition of blend depends on many factors such as market demand, availability of raw materials, and specific requirement of product for the targeted groups etc. Maize, finger millet and elephant foot yam are produced regularly in the state of Chhattisgarh and available in the local market at cheaper price. Maize is a good source of starch, minerals, proteins, vitamin A and vitamin E. Finger millet is rich in nutrient content which is superior to rice and wheat in terms of minerals, polyphenols, protein, fiber and vitamins. Elephant foot yam has also good sources of nutritional as well as medicinal value. These commodities have not been explored properly by the food scientists and technologists for value addition and development of novel foods. In the past much of the work has been done on the development of extruded products with various combinations of ingredients. Importantly the nutritional balance or the health benefits have not been considered well while combining or selecting the ingredients. Considering the availability of finger millet and elephant foot yam easily at a cheaper price, the present piece of work was planned to develop extruded snack food in combination with maize and defatted soy flour. Accordingly, based on the preliminary experiments, the levels of three major ingredients namely maize, finger millet and defatted soy were varied in the range of 40 to 55%, 20 to 30%, and 10 to 25%, respectively and that of elephant foot yam was kept constant (10%). The ratio of ingredients was designed using D-optimal mixture design for the formulation of composite blend. The extruded products were developed using a laboratory model co-rotating twin screw extruder (BTPL Lab model) keeping the process variables constant as: barrel temperature (100oC), screw speed (300 rpm), feed rate (24 rpm), die diameter (3 mm) and feed moisture content (15% wb). The physical and functional properties like expansion ratio (ER), bulk density (BD), hardness (H), water absorption index (WAI) and water solubility index (WSI) of extruded products were evaluated to understand the effect of ingredient levels on quality parameters of the products. The variation of blend composition due to variation in ingredients level significantly affected the physical and functional properties of the extruded product. The ER, BD, hardness, WAI and WSI of extruded products were found to be varied in the range of 2.42 - 3.30, 0.14 -0.26 g cm-3, 11.15 - 18.67 N, 5.57 - 6.87 g g-1 and 14.42 - 19.95%, respectively. Composite blend comprising of different ingredients in the ratio of 40:30:20:10 (MF:FM:DS:YP) was found to be an optimum with a desirability function of 0.82. Product developed with this blend composition exhibited encouraging values of the quality indicators viz., ER = 3.29, BD = 0.14 g cm-3, hardness = 11.94 N, WAI = 6.13 g g-1 and WSI = 17.07%. Central composite rotatable design (CCRD) was used with optimum composite blend to study the effect of varying levels of process variables on different quality indicators of the extruded product (product moisture (PM), expansion ratio (ER), bulk density (BD), hardness, crispness (Cr), WAI and WSI). The range of variables considered for the experiments were as barrel temperature (100-150oC), screw speed (110-350 rpm) and feed moisture (12-20% wb). The design (CCRD) consisted of 20 experiments. Analysis of the variance (ANOVA) and regression equations for all the responses was obtained using Design Expert Software (version 10.0.5.0). The process parameters were optimized by setting the goals to obtain desired quality product using the same software. The ANOVA indicated that the physical and functional properties of the extruded product were significantly influenced by the process variables. The values of different attributes were found to be in the range of product moisture = 6.14 - 9.78% (wb); expansion ratio = 2.017 - 3.391; bulk density = 0.13 - 0.28 g cm-3; hardness = 12.43 - 19.04 N; crispness = 10 - 25 fractures; WAI = 5.76 - 7.25 g g-1 and WSI =12.76 - 20.97%, respectively. Based on the response data obtained through these 20 experiments, the optimum condition of the variables was determined as feed moisture: 14%, barrel temperature: 110oC and screw speed: 301 rpm. The product developed with such optimum condition of the variables was rated with quite high value of sensory score (8.2 overall acceptability) having a desirability level of 0.712. The proximate composition of the product with optimized composite blend and optimum level of process variables had 16.33% protein, 0.63% fat, 4.51% ash, 2.58% fiber, 69.40% carbohydrate and 6.55% moisture. Developed extruded product was also subjected to study the moisture sorption behaviour which was accomplished by static method of sorption for the temperature and humidity range of 30-60°C and 11-92% RH. The sorption behaviour of the product represented the typical type II curves like other similar food materials. GAB model of isotherm was found to be adequate to describe the experimental data on sorption behaviour of product for the range of RH studied. The EMC of the extruded product varied from 2.46 to 30.05% in the experimental range of relative humidity and temperatures. The shelf-life of extruded products was determined under accelerated condition (40°C and 90% RH) of storage using four different packaging materials (LDPE, HDPE, Al foil and MPET) for a period of 90 days. The variation in moisture content, hardness and crispness of product was recorded to be the least for the samples packed in MPET over the period of storage compared to all other packaging materials. The result indicated that the product had a shelf-life of 35 days without appreciable variation in the quality characteristics under accelerated conditions in MPET packages which can be manifold under normal condition of storage.
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DEVELOPMENT AND CHARACTERIZATION OF MAIZE-FINGER MILLET BASED PROTEIN ENRICHED EXTRUDED PRODUCTS
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