Extensional Flow Characteristics of Milk and Soy Set Yogurts with Polysaccharide Additives

Abstract

The extensional flow characteristics of milk and soy set yogurts were investigated using lubricated squeezing flow viscometry. The samples were compressed by a flat probe in a Lloyd Universal Testing Machine. Nine treatments were tested with different total solids (13, 18, 23%), different agar additions (0.1, 0.5, 1%) and different carrageenan additions (0.1, 0.2, 0.3%). Soy yogurt with agar addition elicited soft gel formation. Soy yogurt with carrageenan addition exhibited syneresis and viscous flow behavior. Compared to milk yogurt, yield stress values of soy yogurt were higher and reached a higher biaxial strain rate. With increasing solids content, yield viscosity values increased. The addition of increasing amounts of agar to both soy and milk yogurts also increased yield viscosity. However, unlike milk yogurt, soy yogurt with agar addition elicited lower yield viscosity values than plain soy yogurt. In contrast to soy yogurt, adding carrageenan resulted in higher yield viscosity values compared to plain milk yogurt. Yet, increasing amounts of carrageenan tended to reduce yield viscosity for both yogurts. The manipulation of the additives can be a useful determinant for the texture and sensory properties of soy yogurt as well as milk yogurt.