RHEOLOGICAL STUDY ON ICE CREAM

Abstract

This work was implemented to study the effect of whey protein concentrate (WPC), whey protein isolate (WPI) and glycomacropeptide (GMP) as a partial substitution of milk solids not fat (MSNF) in ice cream formula by 1, 2, 3 and 4% of (MSNF). Mixes and resultant ice cream samples were analyzed for their chemical, physicochemical and rheological properties as well as the sensory quality attributes. There was no remarkable effect of adding whey proteins as partial substitution of MSNF on total solids or fat percentages, while total protein, ash, and lactose content were significantly affected. Specific gravity was significantly affected with the ratio of substitution in both mixes and resultant ice cream and therefore the weight per gallon and overrun percent were significantly changed in the samples. Apparent viscosity as well as flow time of mixes were significantly increased. Flow behavior was also affected showing higher yield stress. Increasing WPC, WPI and GMP in ice cream mixes resulted in a building up of structure leading to increase in the sample viscosity. The shear stress increased significantly with increasing the substitution ratio. Also, flow behavior index (n) decreased by increasing the substitution levels of whey proteins. The consistency coefficient (k) was more affected by the presence of whey proteins in the recipe than the flow behavior index. Herschel-Bulkley behavior (building up of structure and increasing of sample viscosity) was observed in ice cream mix by increasing the substitution levels of whey proteins. Back-extrusion results represented a decrease in hardness values of resultant ice cream, while, during storage, there was a slight increase. Energy input values decreased by increasing substitution levels of whey proteins. During storage, there was a low significant increase of energy input values. The energy output negatively correlated with substitution levels of whey proteins and positively with storage period indicating a strong structure for stored ice cream. Load at target deformation (50%) applied to the samples showing decreased values proportional to increasing substitution levels of whey proteins in ice cream samples when fresh and after 14 days storage. The resilience showed decreased ratio indicating more visco