Functional and Pasting Properties of Composite Flour from Wheat, Sweet Potato and Soybean

Wheat (Triticum spp.) is the most popular cereal grain that is consumed worldwide. It is the most important stable food crop for more than one third of the world population and contributes more calories and proteins to the world diet than any other cereal crops (Shewry et al., 2009). Wheat is the leading crop due to the elastic property of gluten which is essentially used for the production of numerous baked products such as bread, biscuits, cookies, doughnuts and cakes, of which bread is the most common among them (Dewettinck et al., 2008). Many people like wheat-based products because of the taste, and particularly the texture. Wheat is unique among cereals because its flour possesses the ability to form a visco-elastic dough when mixed with water Sweet potato (Ipomea batatas), is a root crop that is grown in developing countries especially the tropics and subtropics. It is high yielding, but bulky and perishable because of its moisture content. However, because of its high dry matter yield, it could be an attractive source of flour in many places if efficient, economical methods of drying could be found. Sweet potato is high in carbohydrates, vitamins (A and C), calories, minerals and precursor of vitamin A (Antonio et al., 2011). According to Akoroda (2009), it provides food security and farmers in Africa produce about 7 million tons of sweetpotato each year of which the majority are lost due to improper postharvest handling.

Soybean is a leguminous vegetable of the pea family that grows in tropical, subtropical, and temperate climates. It was domesticated in the 11th century BCaround northeast of China. It is believed to have been introduced to Africa in the 19th century by Chinese traders along the east coast of Africa (IITA, 2015). The eastern half of North China in the eleventh century B.C. has been traced to the first domestication of soybean. Islam et al. (2007) reported that soybean is one of the most important oil and protein crops of the world of which Serrem et al. (2011) also stated that it contains 30 to 45% protein with a good source of all indispensable amino acids. The protein content of soybean is about 2 times of other pulses, 4 times of wheat, 6 times of rice grain, 4 times of egg and 12 times of milk. Soybean has 3% lecithin, which is helpful for brain development. It is also rich in calcium, phosphorous and Vitamins A, B, C and D.It has been referred to as “the protein hope of the future” (Islam et al., 2007).

The growing concern about a healthier lifestyle and healthy foods has necessitated the food industries to utilize indigenous food to create new products. In essence, various processing technologies have helped in transforming food ingredients into healthier products with maximum nutritional value to ensure nutrient security of the population in developing countries (kumar, 2010). Hasmadi et al. (2014) stated that composite flour is considered advantageous in developing countries as it reduces the importation of wheat flour and encourages the use of locally grown crops as flour.

Functional properties are the fundamental physico-chemical properties that reflect the complex interaction between the composition, structure, molecular conformation and physico-chemical properties of food components together with the nature of environment in which these are associated and measured (Siddiq et al., 2009). Functional characteristics are required to evaluate and possibly help to predict how new proteins, fat, fibre and carbohydrates may behave in specific systems as well as demonstrate whether or not such protein can be used to stimulate or replace conventional protein (Siddiq et al., 2009).

The pasting property is one of the important starch physicochemical properties and is affected by multiple factors (Bemiller, 2011). According to Srichwong et al. (2005) starch pasting properties are highly influenced by the composition proportion and structure of starch (e.g. total starch as well as amylose and amylopectin content, the ratio of amylose and amylopectin, the proportion of starch granules with distinct size, distribution of chain length).

This work is aimed at studying the functional and pasting properties of composite flours of wheat, sweet potato and soybean.