Effect of whey and soy proteins fortification on the textural and rheological properties of value-added yogurts

Abstract

The objective of this study was to develop whey and soy proteins fortified value-added yogurts based on their textural and rheological properties to meet a high demand to increase protein content of conventional yogurts for many health benefits. Seven yogurts (control, 1, 3 and 5% of whey/soy proteins) were developed by fortifying with whey and soy proteins. The protein fortified yogurts were compared with control (without protein fortification) for their textural and rheological properties. The dynamic viscosity of yogurts was determined, and the shear stress-shear rate relationship was modeled using a power law equation to determine the apparent viscosity and flow behavior of yogurts. There was a significant effect of protein fortification on the textural and rheological properties of yogurts (p < 0.05). The textural properties and viscosities of 1-5% soy protein fortified samples were close or better to control. Textural and rheological properties of the yogurts indicated that up to 5% soy protein could be incorporated for the quality yogurts. whereas only 1-3% whey fortification of yogurt was possible because 5% whey protein created aggregates and syneresis of yogurts. Power law modeling could predict the shear stress and shear rate relationship and apparent viscosity of all yogurts with an accuracy of 80-99% depending on level of protein fortification and protein type. Dynamic viscosity and apparent viscosity of all yogurts decreased with shear rate. Power law (n < 1) showed that all yogurt samples were shear thinning products. The desired viscosity could be obtained using an optimum protein fortification. The study indicated that soy protein could be used as an alternative to whey protein for the improved protein fortified yogurt production.