Effect of whey protein phase volume on the tribology, rheology and sensory properties of fat-free stirred yoghurts

摘要

A series of fat-free yoghurts were made from milks formulated for constant protein (5%) and lactose (6%) content and casein to whey protein ratios ranging from 80:20 (Control) to 50:50. Yoghurts were evaluated for their particle size, microstructure, rheology and tribology using instrumental techniques, and their sensory properties were evaluated by a trained sensory panel using a texture focused vocabulary of 19 attributes. Frictional properties and yield stress increased with an increasing phase volume of whey protein, resulting in a more heterogeneous microstructure observed through Confocal microscopy. Analysis by tribology suggests that the dominating factor controlling lubrication in the Control yoghurt was the continuous homogenous protein network formed between whey proteins linked to casein micelles. However, the serum phase of the yoghurt had a greater influence on friction as the proportion of whey protein was increased, and the nature of the protein network changed to have larger voids between aggregates. Significant sensory differences were found for most attributes between the yoghurts containing the highest (50%) and lowest (20%) proportion of whey protein. Perceived creaminess and smoothness in-mouth decreased with whey protein content. Although the highest whey protein yoghurt was perceived most lumpy and the thickest in-spoon for visual appearance, there were no differences between samples in perceived thickness in-mouth. There were high correlations between particle size and geometric sensory properties (positive correlations with granular and lumpy attributes, negatively correlated with smoothness and adhesiveness), and also between friction and sensory properties, notably at 0.1 mm s(-1). (C) 2017 Elsevier Ltd. All rights reserved.