Effect of concentration of culture on incubation time, storage and sensory characteristics of set yoghurt

Yogurt is a coagulated milk product, mostly obtained by the action of two bacteria, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. Yogurt is considered as a complete food largely consumed by both children and elders. It contains all the essential nutrients as required by human beings along with some beneficial live microorganisms. A variety of yoghurt is made of milk from different breeds. In this study milk from Sahiwal, Holstein Friesian and Nili-Ravi buffalo were used. The objective was to study the effect of culture concentration on different attributes of yoghurt made from different blend of milk for process optimization. Milk was standardized, using skimmed milk powder (SMP), to 15% total solids (TS) with 3.5%fat. Milk was pasteurized at 82oC for 5 minutes and then cooled down to 43oC and starter culture was added @ 0.9%, 1% and 1.1% respectively. Yogurt batch was incubated at 43oC for 3 to 3.5 hours. During this period pH was monitored regularly and as pH drops to 4.6, the batch was shifted to blast chilling at 1-2oC and then stored at 4oC. All the samples were analyzed for TS, fat, acidity, syneresis, viscosity and sensory characteristics at day 1, 7, 14 and 21 respectively. The results showed that yoghurt made from 1% culture were of high attributes as compared to 0.9 and 1.1% culture concentration. Milk source was also having a significant effect on yoghurt quality. Yoghurt made from 100% Nili Ravi buffalo milk (To) with a culture concentration of 1% was of superior quality followed by T3, T4, T1, T5 and T2, respectively.