Effects of whey and soy protein addition on bread rheological property of wheat flour.

The development of wheat-based foods that are enriched with proteins is increasingly popular due to consumer demand regarding food nutritional content and quality. This study was performed to compare the effect of whey and soy protein on the rheological properties of wheat dough and bread-making quality in a relatively wide range of protein addition (0-30%). We found that the incorporation of whey protein (WP) decreased dough stability time (MST), minimum torque (MMT), G' and G″, but increased dough peak torque (MPT), stickiness, G' and G″ in temperature sweep. With the increasing level of WP from 0 to 30%, the specific volume of bread initially decreased from 2.61 to 2.22 cm3 /g, then increased to 3.08 cm3 /g when WP was at higher concentration than gluten. However, the crumb hardness increased from 173 to 1291 g at the same time. As a contrast, the addition of soy protein (SP) increased dough MST, MMT, G' and G″, but decreased MPT, stickiness, G' and G″ in temperature sweep. With the increasing level of SP from 0 to 30%, the specific volume of bread decreased from 2.61 to 1.31 cm3 /g and the hardness first decreased from 173 to 152 g, then increased to 696 g. The results suggested that selection of the protein source and amount with appropriate functionalities played an important role in certain applications for protein fortified bakery products. PRACTICAL APPLICATIONS: Since it is known that the gluten network is responsible for viscoelastic properties in wheat dough and for dough structure strength and gas retention, most studies reported that enrichment of foreign proteins interfered with gluten development and therefore, had negative effects on bread quality. This study compared the effects of whey and soy proteins on the thermomechanical, dynamic rheological and microstructural properties of wheat dough and bread-making quality in a relatively wide range of protein addition (0-30%). The results suggested that selection of the protein source and amount with appropriate functionalities significantly affected the structure of the dough and quality of the bread. Our study is essential for product development and process control when considering the popularity of protein fortified bakery products.