The individual and interactive effects of skimmed milk powder, lactose, and sodium ascorbate on the number of viable cells and freeze-drying survival for vacuum freeze-dried powder formulation of Lactobacillus bulgaricus were studied by response surface methodology, and the optimal compound lyoprotectant formulations were gained. It is shown that skim milk powder, lactose, and sodium ascorbate had a significant impact on variables and survival of cultures after freeze-drying. Also, their protective abilities could be enhanced significantly when using them as a mixture of 28% w/v skim milk, 24% w/v lactose, and 4.8% w/v sodium ascorbate. The optimal freeze-drying survival rate and the number of viable cells of Lactobacillus bulgaricus were observed to be (64.41±0.02)% and (3.22±0.02)×10(11) colony-forming units (CFU)/g using the optimal compound protectants, which were very close to the expected values 64.47% and 3.28×10(11) CFU/g.
In order to obtain the optimum parameters of fermentation for goat milk, the effect of inoculum and incubation temperature on the fermentation of yogurt strains was studied by measuring acidity, pH and viable bacterial counts by single factor test. Inoculum (v/v) was 1, 3, 5, 7 and 9%, respectively. Incubation temperature was 37, 39, 41, 43 and 45°C, respectively. The results were as follows: lower or higher inoculum and incubation temperature resulted in adversely influence on overall properties of goat yogurt. The optimum inoculum in goat milk was 3% and incubation temperature 43°C, respectively.
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