Consistency, microstructure and probiotic survivability of goats' milk yoghurt using polymerized whey protein as a co-thickening agent

A probiotic goats' milk yoghurt was developed containing Lactobacillus acidophilus, Lactobacillus casei and Bifidobacterium spp. and using polymerized whey protein (PWP, 0.4%) and pectin (0.3%) as gelling agents. The yoghurt was analyzed for chemical composition, mould and yeast counts, changes in pH, titratable acidity, and viscosity, and probiotic survivability during storage at 4 degrees C. There was no significant difference in viscosity between weeks; however, changes in titratable acidity and pH showed significant differences between weeks during storage. L. casei and Bifidobacterium spp. remained viable with populations above 10(6) cfu g(-1) during storage, but there were no viable counts of L. acidophilus by the fourth week. Scanning electron microscopy of goats' milk yoghurt revealed that PWP interacted with casein micelles to form a comprehensive network in the yoghurt gel. Results indicated that PWP may be a novel protein-based thickening agent for improving the consistency of goats' milk yoghurt and other products. (C) 2011 Elsevier Ltd. All rights reserved.