Physiochemical Properties, Microstructure, and Probiotic Survivability of Nonfat Goats' Milk Yogurt Using Heat-Treated Whey Protein Concentrate as Fat Replacer.

There is a market demand for nonfat fermented goats' milk products. A nonfat goats' milk yogurt containing probiotics ( Lactobacillus acidophilus, and Bifidobacterium spp.) was developed using heat-treated whey protein concentrate (HWPC) as a fat replacer and pectin as a thickening agent. Yogurts containing untreated whey protein concentrate (WPC) and pectin, and the one with only pectin were also prepared. Skim cows' milk yogurt with pectin was also made as a control. The yogurts were analyzed for chemical composition, water holding capacity (syneresis), microstructure, changes in pH and viscosity, mold, yeast and coliform counts, and probiotic survivability during storage at 4 °C for 10 wk. The results showed that the nonfat goats' milk yogurt made with 1.2% HWPC (WPC solution heated at 85 °C for 30 min at pH 8.5) and 0.35% pectin had significantly higher viscosity ( P < 0.01) than any of the other yogurts and lower syneresis than the goats' yogurt with only pectin ( P < 0.01). Viscosity and pH of all the yogurt samples did not change much throughout storage. Bifidobacterium spp. remained stable and was above 106CFU g-1 during the 10-wk storage. However, the population of Lactobacillus acidophilus dropped to below 106CFU g-1 after 2 wk of storage. Microstructure analysis of the nonfat goats' milk yogurt by scanning electron microscopy revealed that HWPC interacted with casein micelles to form a relatively compact network in the yogurt gel. The results indicated that HWPC could be used as a fat replacer for improving the consistency of nonfat goats' milk yogurt and other similar products. [ABSTRACT FROM AUTHOR]