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CHAPTER ONE
1.0. INTRODUCTION
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants as an energy store. It is most common carbohydrate in human diets and is contained in large amounts in such staple foods as potatoes, wheat, maize, rice, and cassava. Pure starch is a soft, white, tasteless and odorless powder that is insoluble in cold water, alcohol or other solvents. It consists of two types of molecules, the linear and helical amylase and the branched amylopectin. Depending on the plant, starch generally contains 20 to 25% amylase and 75 to 80% amylopectin by weight. (Brown and poon, 2005).
Starch is one of the most abundant carbohydrates in nature and present in many foods plants. Starch is by far the most consumed carbohydrates in the human diet. Traditional staple foods such as cereals roots and tubers are the main source of dietary starch. It is one of the main energy sources in our diet. Chemically starch is a polysaccharide consisting of a large number of glucose molecules. (Nugent 2005).
Modified starch also called starch derivatives are prepared by physically, enzymatically or chemically treating native starch to change its properties. Starches are modified to enhance their performance in different applications. Starches may be modified to increase their stability against excessive heat, acid, shear, time, cooling or freezing, to change their texture, to decrease or increase their viscosity, to lengthen or shorten gelatinization time or to increase their visco –stability. (Vickieetal, 2007).
Modified starches are mild, nature derived thickeners which provide stable viscosity under either very low or high PH conditions, and are stable to homogenization, high heat, and freezing conditions. It is also a cold – water soluble, pregelatinized or instant starch which thickens and gels without heat or a cook- up starch which must be cooked like regular starch. Other starch derivates are glucose, high fructose syrup and glucose syrups, starch degraded with amylase enzyme to make a sweetener. (WWW. Cargill. Com 2014)
Starch modification is a changed of native starch’s property to be in accordance with certain application. For instance, modified starch with a shear force resistance means that it is able to be processed without any change to viscosity and texture. Furthermore starch modification can help improve texture and reduce retrogradation, gelatinization and syneresis as well as increase freeze – thak stability. (WWW. ttimico.th 2013)
Starch is modified through a number of different methods, such as physical and chemical modification.
Physical modification is carried out by heating and then instantly drying the starch with a drum dryer or spray dray to change its property. It provides advantages in terms of requiring no chemical process (no. E - numbers). Which makes it more acceptable in many countries. While
Chemical modification involves a chemical reaction between the native starch and specific. Chemical for improving the starch’s property. It can be divided into derivertization, cross linking, size reduction with acid thinning oxidation and enzymatic hydrolysis and dextrinization. (WWW. ttim. Co.th 2013)
Cassava (Manihot esculenta crantz) is one of the most important staple foods crops grown in tropical Africa. It plays a major role in efforts to alleviate the Africa food crisis because of its efficient production of food energy, year – round availability tolerance to extreme stress conditions and suitability to present farming and food systems in African (Hahn and Keyser 1985, Hahn et al, 1987).
Cassava is the third largest source of food carbohydrates in the tropics after rice and maize. Cassava is a major staple food in developing world, providing a basic diet for over half a billion people. It is one of the most drought tolerant crops, capable of growing on marginal soils. Nigeria is the world largest producer of cassava, while Thailand is the largest exporter of dried cassava. (Fauquet and fargette, 1990)
Cassava roots are very rich in starch and contain significant amounts of calcium (50mg/100g), phosphorus (40mg/100g)and vitamin C (25mg/100g). However, they are poor in protein and other nutrients. In contrast, cassava leaves are a good source of protein (rich in lysine) but deficient in the amino acid methionine and possibly tryptophan. (Ravindran, and Velmerugu, 1992)
Yam (Dioscorea species) is the common name for some plant species in the genus Dioscorea, to the Dioscoreaceae family that form edible tubers. These are perennial herbaceous vines cultivated for the consumption of their starchy tubers in Africa, Asia, Latin America, the Caribbean and Oceania. Yams of African species must be cooked, to be safely eaten, because various natural substances in raw yams can cause illness if consumed. The most common cooking method in Western and Central Africa is by boiling, frying and roasting the yam. Yams have a very starchy and slippery texture. Creamy or firm when cooked, yams have an earthy, hardy taste and usually a minimal amount of sweetness. The tubers can be stored up to six (6) months without refrigeration, which makes them a valuable resource for the yearly period of resource for the yearly period of food scarcity at the beginning of the wet season. Yam is the second most important root/tuber crop in Africa. (Mignouna, et al, 2003)
AIM
The aim of this research work is to compare the qualities of modified starches from cassava and yam.
OBJECTIVES
The objectives of this research work entails:-
To promote consumers interest towards using starch produced from cassava and yam.
To process starch (modified) that can be used without any after effect.............
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