Add 7% of the sugar in milk, Nisin will be added in accordance with the 0. 3, 0.6, 0.9 IU / ml, then added to the mixture of milk and sugar, fully dissolving and homogenizing, sterilization after cooling to 42℃, Strains added quantity in 0.2 U/kg according to the aseptic operation.
Slow shake, fermentation at 42℃. Ends fermentation when it reaches 70 ~ 75℃, after cooling with ice water and then mixing, refrigerated under 4 ℃ environment.
In 1st, 7th, 14th, 21st, 28th day, check the number of living bacterium of lactic acid bacteria in yogurt.
The number of viable cells of lactic acid bacteria with different content of Nisin was the highest at the first day after fermentation, and the number of viable bacteria of lactic acid bacteria without Nisin was the highest, and increased first and then decreased on the 1st to 14th day within shelf-life.The content of Nisin was 30IU / mL Of the lactic acid bacteria live samples of yogurt changes in the trend and the trend of the contrast sample is basically the same. Nisin 60 IU / mL yogurt samples in the shelf life of 14th days to 28th days viable cell count decreased more slowly. Nisin content of 90 IU / mL in the shelf life of lactic acid bacteria in yogurt have a certain impact, compared with other groups of lactic acid bacteria, decreased significantly.
Polylysine is an ideal natural antimicrobial to prolong the shelflife, with a high natural antimicrobial activity against a wide range of fungi, Gram-positive and Gram-negative bacteria and their spores.