Thesis Abstract

Abstract
Sorghum bicolor, commonly known as sorghum, is an important cereal crop widely cultivated for its grains. In this research study, the effect of steeping period on the yield and acceptability of starch extracted from white and red varieties of sorghum bicolor was investigated. The white and red sorghum varieties were selected due to their significant differences in color, which may also reflect variations in starch properties. Steeping, the process of soaking grains in water to soften and separate the starch, is a crucial step in starch extraction. The experimental design involved steeping both white and red sorghum grains for different periods ranging from 6 to 24 hours. The steeped grains were then processed to extract starch, which was subsequently analyzed for yield and quality characteristics. Yield was determined based on the amount of starch extracted relative to the initial weight of the sorghum grains. Acceptability of the extracted starch was evaluated through sensory analysis to assess factors such as color, texture, and taste. The results revealed that the steeping period had a significant impact on both the yield and acceptability of starch extracted from the white and red sorghum varieties. A longer steeping period generally led to higher starch yields due to increased starch solubilization and separation from the grain matrix. However, prolonged steeping beyond a certain point was found to negatively affect the acceptability of the extracted starch, particularly in terms of color and taste. Interestingly, the white and red sorghum varieties exhibited differences in starch yield and acceptability profiles in response to varying steeping periods. The white variety consistently yielded higher starch content compared to the red variety across all steeping durations. In terms of acceptability, sensory evaluation indicated that the white sorghum starch was preferred for its lighter color and milder taste compared to the red sorghum starch. Overall, this study highlights the importance of optimizing the steeping period in starch extraction processes to achieve both high yield and desirable quality attributes. The findings also underscore the influence of sorghum variety on starch characteristics, emphasizing the need for tailored processing methods based on specific cultivars. Further research could explore additional factors affecting starch extraction from sorghum and investigate potential applications of the extracted starch in food and industrial sectors.

Thesis Overview

1.0 INTRODUCTIONStarch is non-crystalline white powder, insoluble in cold water.It can be hydrolysed into simpler molecules by either heating with an acid or a suitable enzyme. (Awan and Okaka, 1983). Starch is the major storage form of carbohydrate in sorghum and millets. It consists of amylopectin, a branched - chain polymer of glucose, and amylose, a straight chain polymer (FAO, 1992).The digestibility of the starch, which depends on hydrolysis by pancreatic enzymes, determines the available energy content of cereal grain. Processing of the grain by methods such as steaming, pressure cooking, flaking, puffing or Micronesian of the starch increases the digestibility of sorghum starch.This has been attributed to a release of starch granules from the protein matrix rendering t hem more susceptible to enzymatic digestion (FAO, 1992).When starch is heated in water (moist heat) it will produce a gel - an important property needed in the thickening of gravies, sauces, in the baking of bread and production of custards (Awan and Okaka, 1983).The physico-chemical properties of the starch affect the textural characteristics of the food preparations made from the grain.The behaviour of starch in water is temperature and concentration dependent (Malleshi and Desikachar, 1985).Starches in general show very little uptake of water at room temperature and their swelling power is so small. At higher temperature, water uptake increases and starch granules collap- which leads to solubilisaiton of amylose and amylopectin to form a colloidal solution. This is the gelatinisation stage. Genetic and environmental factors affect the gelatinisation temperature of starch (Freeman and Bocan, 1973).Heat treatment of starch in a limited amount of water lead to swelling the granules with very little loss of soluble material and partial gelatinization of the starch (Watson, 1970).On cooking, the gelatinized starch tends to return from the soluble, dispersed and amorphous state to an insoluble crystalline state.This phenomenon is known as retrogradation or set back; it is enhanced with low temperature and high concentration of starch (Rooney, 1991). Amylose, the linear component of the starch, is more susceptible to retrogradatioln than the amylopectin (Freeman and Bocan, 1973).1.1 STATEMENT OF THE PROBLEM Steeping of sorghum for a longer period consumes time and imparts undesirable flavour to the starch extracted from the sorghum due to the action of some spoilage microorganisms. Hence the need to reduced the steeping time and detect its effect on the yield and their sensory properties.1.2 OBJECTIVE OF STUDY The overall objective of the project work is to develop a process for extracting starch from two different cultivar of sorghum by subjecting to different steeping time.The null hypothesis is that cultivar and steeping period will not have effect on the yield and functionality of the extracted starch.Specific aims are:To determine the effect of steeping period on:1. The yield of the starch2. The functional properties of the starch3. Organoleptic properties of the starch4. The glycosidic cyanide level of the starch5. The metabolysable energy value of the starch