Characteristics of Yam Composite Flour: Properties and Function of Bread and Tortilla Making

Abstract

Consumer interest in dietary fiber is on the rise as more information about its potential impact on health has become available. Flour from yam (Dioscorea rotundata) could have useful applications in the baking industry, in composite flour blends, because of its high level of dietary fiber and other essential nutrients. Study of the chemical composition, physicochemical characteristics, and pasting properties of unfermented-white yam flour (UYF) and fermented-brown yam flour (FYF) were investigated. Studies show that composite flour from yam has high ash, total starch, and fiber content than refined wheat flour. Thermal studies showed the energy required for composite flour gelatinization is greater than that of refined wheat flour. The firmness of FYF gel significantly increased with increasing number of days unlike UYF where slight hardness in texture was observed. This study revealed that each flour type exhibited different characteristics when compared to refined wheat flour. This necessitates further studies to substitute the yam flour samples with refined wheat flour to create composite flours that could be employed in bakery products. Inclusion of UYF and FYF flour at 5, 10, 15 and 20% levels of substitution with wheat flour affect the dough physicochemical, rheological pasting properties, and the nutritional quality. Proximate analysis of the flours carried out shows composite flours were of lower protein value but had higher fiber content than refined wheat flour. Impact on the gluten quality, gassing power, farinograph parameters was observed. The farinograph water absorption increased significantly (p<0.05) for blends prepared with UYF. Investigation revealed that the end-product quality (oven spring, loaf volume, bread crumb, tortilla weight, flexibility, thickness and color) of bread loaves and tortilla was significantly affected. This study demonstrated that incorporation of up to 10% FYF flour appears to give acceptable dough with good viscoelastic properties and bread with quality traits similar to refined wheat bread. This might be because bread itself is a fermented bakery product. For the tortilla; an unfermented product, 20% UYF inclusion seems to be more suitable to produce tortillas with good extensibility, acceptable thickness and whiteness with no dark spots that will appeal to the consumers.