EFFECTS OF PROCESSING METHODS ON THE PHYSICO-CHEMICAL PROPERTIES OF SWEET POTATO AND SORGHUM

CHAPTER ONE

INTRODUCTION

Sweet potato (Ipomoea batatas) is an important food crop in the tropical and sub tropical countries and belongs to the family convolvulaceae. It is cultivated in more than 100 countries. ( Woolfe, 1992). Nigeria is the third largest producer in the world with china leading, followed by Uganda. Sweet potato ranks seventh among the world food crops, third in value of production and fifth in caloric contribution to human diet (Bouwkamp, 1985). Sweet potatoes are rich in dietary fibre, minerals, vitamins and anti oxidants such as phenolic acids, anthocyanins, tocopherol and ß- carotene. Besides acting as anti oxidants, carotenoids and phenolic compounds also provide sweet potatoes with their distinctive flesh colours ( cream, deep yellow, orange and purple). Sweet potato blends with rice, cowpea and plantain in nigerian diets. It is also becoming popular as a substitute to yam and garri. It can be reconstituted into fofoo or blended with other carbohydrate flour sources such as wheat ( Triticum aestivum) and cassava ( Manihot esculenta) for baking bread, biscuits and other confectioneries (Woolfe, 1992).

The leaves are rich in protein and the orange flesh varieties contain high beta carotene and are very important in combating vitamin A deficiency especially in children.

Sorghum (sorghum bicolor (S. bicolor) is a tropical plant belonging to the family of poaceae, is one of the most important crops in Africa, Asia and Latin America. More than 35% of sorghum is grown directly for human consumption.

The rest is used primarily for animal feed, alcohol production and industrial products ( FAO, 1995). The current annual production of 60 million tons is increasing due to the introduction of improved varieties and breeding conditions. Several improved sorghum varieties adapted to semi-arid tropic environments are released every year by sorghum breeders. Selection of varieties meeting specific local food and industrial requirements from this great biodiversity is of high importance for food security. In developing countries in general and particularly in West Africa demand for sorghum is increasing. This is due to not only the growing population but also to the countries policy to enhance its processing and industrial utilization.

More than 7000 sorghum varieties have been identified, therefore there is a need of their further characterization to the molecular level with respect to food quality. The acquisition of good quality grain is fundamental to produce acceptable food products from sorghum. Sorghum while playing a crucial role in food security in Africa, it is also a source of income of household . In West Africa, ungerminated sorghum grains are generally used for the preparation of "to", porridge and couscous. Malted sorghum is used in the process of local beer "dolo" (reddish, cloudy or opaque), infant porridge and non fermented beverages. Sorghum grains like all cereals are comprised primarily of starch.

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