The combined effects of whey protein isolate concentrated and low temperature with nisin on survival of Bacillus licheniformis in imitated milk solution

Combined effect of whey protein isolate and low temperature with nisin on survival of Bacillus licheniformis were investigated. Sterile imitated milk solution prepared from casein, milk fat, lactose and distilled water was mixed with different whey protein isolate levels of 0, 1, 2 and 4% (w/v) and 100 IU/ml nisin. After mixed thoroughly, the milk solution was aseptically inoculated with 3.74-3.78 log cfu/ml Bacillus licheniformis, pasteurized at 72oC for 15 s, cooled down and subsequently stored in low temperature at 4 and 10oC for 3 weeks. The results clearly demonstrated that B. licheniformis had a better growth rate at 10oC compared to that at 4oC even in the presence of 100 IU/ml nisin. The presence of whey protein isolate as low as 1% (w/v) could work synergistically with nisin in inhibiting the target organism. The growth of the bacilli in milk solution was accompanied with the development of milk acidity. The outgrowth of the bacilli spores could be inhibited by the presence of nisin and low storage temperatures.