Sourdough and Bread Properties as Affected by Soybean Protein Addition

Abstract

Soybean benefits in human health have been the target of numerous studies during the last decades. This interest has been the result of the findings about soybean consumption, where this legume or some of its components, mainly proteins and isoflavones, have been related to the reduction of some human diseases, such as cardiovascular diseases, diabetes, obesity, hypertension, dyslipidemia or even cancer (Pineiro, 2006; Martin, 2001; Barnes, 1995). Soybean is an economically important crop, which usually has served as a source of energy and good-quality protein for animals and humans, as it presents a high content of protein (36-48%), lipids (18-21%) and carbohydrates (33.5%), besides the amount of crude fibre and non saturated lipids which make them to be considered as healthy foods (Chavez et al., 1992). Moreover, a number of nutrients and micronutrients with neutraceutical properties have been identified in soybean, including isoflavones, phytosterols, inositol hexaphosphate, saponins, protease inhibitors, and bioactive peptides (Barnes, 1995; Hawrylewicz et al., 1995; Kennedy, 1995; Rao & Sung, 1995; Badger et al., 2005; Galvez et al 2001; Vucenik et al., 2003; Badui, 1993). Nowadays, different kinds of foods containing soybean flour or some of its products can be found in the market, being bread one of these items. Adding soybean to bread has been proposed to improve its nutritional quality, however, the level of soybean addition has been restricted to less than 10%-15% (wheat flour basis) as detrimental effects on bread quality (lower bread volume, coarser crumb structure, and a stronger flavour) have been reported (Sabanis & Tzia, 2009; Olaoye et al., 2003; Dhingra & Jood, 2004; Shogren et al., 2003; Halle et al, 2004). This effect makes necessary to keep looking for other alternatives that allow higher levels of addition of this legume in bread making. Sourdough breads are very popular foods worldwide. They are a mixture of flour (rye and wheat) and water that is fermented with lactic acid bacteria (LAB), mainly heterofermentative strains, which generate, as fermentation by-products, lactic and acetic acids and hence resulting in a sour taste of the end product. At the same time, yeast fermentation takes place, resulting in the dough expansion. The action of both microorganisms determines the sourdough bread characteristics in terms of acid production, aroma and leavening, resulting in an improvement of the volume, texture, flavour, nutritional value and shelf life of bread. These