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Improvement of Nutritional and Functional Properties of Sorghum-Soybean-Maize Composite Flour by Germination and Fermentation and Its Use as Food Against Malnutrition

Author: Murekatete Nicole
Tutor: HuaYuFei
School: Jiangnan University
Course: Cereals, Oils and Vegetable Protein Engineering
Keywords: Fermentation germination sorghum soybean maize composite flour malnutrition functional properties nutritional properties protein digestibility nutrient density shelf life Saccharomyces Cerevisiae viscosity
CLC: TS210
Type: Master's thesis
Year: 2010
Downloads: 159
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Abstract

Cereal grains are the fruit of plants belonging to the grass family (Gramineae) and they are more widely utilized as food in African countries than in the developed world. In fact, cereals account for as much as 77% of total caloric consumption in African countries, and contribute substantially to dietary protein intake in a number of these countries. A majority of traditional cereal-based foods consumed in Africa are processed by natural fermentation. Fermented cereals are particularly important as weaning foods for infants and as dietary staples for adults. The soybean (Glycine max) is one of the most important food plants of the world, and seems to be growing in importance. It’s a versatile food plant that, if used in its various forms, is capable of supplying most nutrients. It can substitute for meat and to some extent for milk. It is a crop capable of reducing protein malnutrition.The first part has extensively covers the relevant literature review of the current nutrition situation in the world, the importance and practice of germination and fermentation in food processing and finally, the origin, structure, composition and use of sorghum, soybean and maize in human nutrition, with great emphasis on germinated and fermented products. Fermentation and germination are two classical technologies commonly used to improve on the protein digestibility, nutrient density of cereals and enrich the foods in vitamins, minerals and amino acids, either by decreasing the amount of inhibitors or by releasing the nutrients for absorption.The second part covers the germination process of sorghum grain and chemical composition changes observed during germination. Before germination sorghum grain was soaked in 0.1% NaOH solution for 24 hrs, then allowed to germinate for 72hrs at 25℃. Moisture, protein, fat, carbohydrate, and ash content showed significant differences before and after germination. Protein concentration decreased by 10%, ash content from 17.57 to 11.51 mg g-1, while fats content from 26.30 to 23.10 mg g-1. Germination was found to reduce significantly the fiber content from 32.11 to 23.01 mg g-1. The sugars, maltose, glucose, and fructose were found in ungerminated sorghum flour in concentrations of 1.98,0.23, and 0.51 %, respectively but after 72 h of germination, they increased to 5.79,3.18, and 0.82 %, respectively. Germination resulted in a decrease of 95.7% of tannin and in a significant increase in In Vitro Protein Digestibility (IVPD) of 10%, and a decrease in bulk density (BD) of 9.7%. The maximum viscosities were 62 and 221 Brabender Unit (BU) for germinated sorghum (GS) and ungerminated Sorghum (US) respectively, observed at temperatures of 88.8 and 93.2℃. The final viscosities at the end of the final holding period were 75 and 213 BU for GS and US, respectively. Low viscosity in GS implies that more flour could be used when preparing foods such us porridge. Sorghum flour obtained after soaking the grains for 24h in 0.1% NaOH, followed by 72h of germination has undoubtedly better digestibility and nutrient density than US.The composite flour was prepared by mixing,40% roasted soybeans,40% germinated sorghum, and 20% maize. The composite flour was inoculated with bakers yeast (Saccharomyces Cerevisiae) at a concentration of 0.0075 g g-1 and incubated at room temperature. Products, denoted as F12 and F24 were collected at 12 and 24h of fermentation for analysis. Methionine, leucine, valine and tryptophan significantly increased during fermentation, and vitamin C content increased from 7.93 to 60.2 mg kg-1. Lysine, linolenic acid, linoleic acid were both well retained during fermentation. Energy value and in vitro protein digestibility increased from 17 295.8 to 17 561.5 J g-1 and from 695.30 to 830.90 mg g-1, respectively. SDS-PAGE showed that limited protein hydrolysis occurred during fermentation. F12 and F24 showed lower paste stability compared to unfermented composite flour, as indicated by their highest difference between peak viscosity and final viscosity (2 and 6 BU). This indicates that unfermented composite flour would have good potential as an ingredient for food exposed to high temperature and mechanical forces. However, fermented composite flour would have better potential to produce food with high nutrient density due to their low viscosity. The results also showed that during fermentation sucrose, maltose and fructose concentration decreased significantly by 87.2%,37.2% and 9.5% respectively, while glucose concentration increased significantly by 87.3%.Results from microbiological analysis showed that bacterial population proliferation was lower in F12 and F24. Before storage, bacterial population was lower at 78% in F24 than in unfermented composite flour and after 30 days the bacterial population was, lower at 57% in F24 than in unfermented composite flour. Sensory evaluation showed F12 and F24 had the highest score in sourness as expected while the aroma, texture, mouth feel and taste characteristics had highest score in unfermented flour.Therefore, appropriate germination of sorghum grain followed by Saccharomyces cerevisiae fermentation of sorghum-soybean-maize composite flour could be used to improve the functional and nutritional properties of the composite flour as results revealed that the nutritive value improves in terms of vitamins, unsaturated fatty acids and essential amino acids. In addition, the fermented composite flour had better nutrient density, digestibility and shelf life.

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