Effect of Ingredient Variation on Microbial Acidification, Susceptibility to Syneresis, Water Holding Capacity and Viscosity of Soy-Peanut-Cow Milk Yoghurt

Acidification of milk by lactic acid bacteria enhances the aggregation of milk proteins to form yoghurt gels with enhanced texture, colour and viscosity. A three-component constrained mixture design was employed to develop 10 soy-peanut-cow milk (SPCM) formulations which were fermented with Lactobacillus bulgaricus and Streptococcus thermophilus (1:1) into soy-peanut-cow milk yoghurt (SPCY). The effect of ingredient variations on microbial acidification, colour, susceptibility to syneresis, water holding capacity and viscosity were determined. Titratable acidity increased with increasing cow milk content and trends in pH were contrary to titratable acidity. SPCY formulations were yellowish-white in colour. Yellowness and lightness increased with increasing soymilk content. Rheologically all products investigated were non-Newtonian and had better consistencies as cow milk content increased in samples and peanut milk content decreased. The water holding capacities of yoghurt samples increased with increasing soy milk content. Formulations without cow milk were the least susceptible to syneresis.