Studies On Preparation And Application Of Skimed Milk Powder Containing Nisin

This research subject is to prepare skimed milk powder containing Nisin and toapplicate it in dairy products. Research results are as follow:A mutant strain with hight yield of Nisin was obtained from lactococcus lactis 2379 by many mutagenetic treatment with ultraviolet ray and CsCL. Compared with primitive strain , the Nisin potency of the mutant strain was increased by over 32%. Through neutralize test to control pH changes during fermentation, the strain produced at least 3-fold greater bacteriocin in skimed milk culture supplemented with yeast extract} and the Nisin potency was 1800IU/ml. After pasteurized, the skimed milk powder containing Nisin was prepared by using lyophilization. Thermodynamic analysis indicated that the number of reaction degree of heat denaturation of Nisin in skimed milk powder was n=1.8. At temperatures of 70℃, 80℃ ,90℃, 100℃, D values for Nisin denaturation were 184.91min, 77.18min, 21.53min,and 9.37min respectively. With this temperature range,Z value was 22.52, and the apparent active energy was 122.033KJ/mol. LTLT(63 ℃ ,30min)and HTST(85℃ ,15s)pasteurization made the Nisin potency decrease to 86.82%and 98.2%,UHT(115℃ 10min, 130℃2s )sterilization made the Nisin potency decrease to 3.43% and 80.58%. Concentration of 30-70IU/ml Nisin in raw milk was able to inhibit the growth of bacteria and spores-forming bacteria, but the effect of Nisin on the growth of psychrotrophic bacteria was weak; Concentration of 35IU/ml Nisin was able to extend the shelf-life of sterilized milk up to 30 days at 4℃, three times longer than the control group; during fermentation, concentration of 5IU/ml Nisin was able to inhilit the growth of lactic bacteria.