CHAPTER ONE
1.0 INTRODUCTION
Cassava (Manihot esculenta, Crantz), is one of the most important food crops in the humid tropics, being particularly suited to conditions of low nutrient availability and able to survive drought (Burrell ,2003). It is a widely grown crop in most countries in the tropical regions of Africa, Latin America and Asia; and ranks as one of the main crops in the tropical countries (Calpe 2003). Among the starchy staples, cassava gives a carbohydrate production which is about 40% higher than rice and 25% more than maize, with the result that cassava is the cheapest source of calories for both human nutrition and animal feeding (Nyerhovwo, 2004). More than two-third of the total production of cassava is used as food for humans, with lesser amounts being used for animal feed and industrial purposes (Nwokoro et al., 2002). Nigeria alone currently produces over 14 million tonnes annually, representing about 25% of subSaharan Africa’s output (Ayodej 2005). Cassava is the third most important food source in the tropical world after rice and maize, it’s provides calories for over 160 million people of Africa (Pilsen et al.,1991).
However, processing methods such as drying have been found to be effective ways of reducing toxicity in cassava products.
Maize (Zea mays) has become a staple food in many parts of the world, with the total production of Maize surpassing that of wheat or rice. Maize is the most widely grown grain crop throughout the America’s, with 361 million metric tons grown in United States in 2014. Approximately, 40% of the crop-130 million tons is used for corn ethanol.(FAO 1990). Maize is widely cultivated throughout the world, and a greater weight of maize is produced each year than any other grain.(Polsen et al…1991) In 2014, total world production was 1.04 billion tonnes.
Those that are sugar-rich varieties called sweet-corn are usually grown for human consumption as kernel ,white field corn varieties are used for animal feed. Various corn-based human food uses (including grinding into cornmeal or masa, pressing into corn oil, and fermentation and distillation into alcoholic beverages like bourbon whiskey), and as chemical feedstock. Maize is also used in making ethanol and other biofuel.
Structurally, Maize grain( Figure1), largely consists of endosperm that is rich in starch (71%). Both the embryo and endosperm contain proteins but the germ proteins are superior in quality as well as quantity. Zeins are a class of alcohol soluble proteins that are specific to endosperm of maize (Prassana et al., 2001) and are not detected in any other plant part. The maize endosperm consists of two district regions ( Floury endosperm and Horny endosperm )having different physical properties. The aleurone layer is the outer most layer rich in hydrolytic enzymes secreted by specialized cells. Within the aleurone layer is the starch rich endosperm having vitreous and starchy regions. The zein proteins found in vitreous region form insoluble accretions called protein bodies in the lumen of rough endoplasmic reti- culum and towards maturation are densely packed between starch grains (Gibbon and Larkins, 2005). These zeins consist of albumins, globulins, glutelins and prolamins and constitute about 50-60% of maize proteins. The prolamins are rich in proline and amide nitrogen derived from glutamine. All prolamins are alcohol soluble (Shewry and Halford, 2002). The prolamins of maize grain are called zeins and consist of one major class ( α -zeins) and three minor classes ( β , and δ ). The zein fraction α is rich in cystein while β – and -fractions are rich in methionine. These four types α , β and δ constitute about 50-70% of maize endosperm and are essentially rich in glutamine, leucine and proline and poor in lysine and tryptophan. Other proteins such as globulins (3%), glutelins (34%) and albumins (3%) are collectively called non-zeins . The zein fraction in normal maize normally contains higher proportion of leucine (18.7%), phenyla- lanine (5.2%) isoleucine(3.8%), valine (3.6%) and tyrosine (3.5%).
