| Nisin is a small molecule polypeptide produced by lactic acid subspecies of lactococcus lactis,and its bacteriostatic spectrum is more extensive.Studies have shown that Nisin inhibits the growth of food spoilage bacteria at the same time,it will inhibit many yogurt products in the growth of food bacteria,the normal fermentation of yogurt products have a certain hindrance.In this study,Lactobacillus isolated from commercially available yogurt products was selected as the test strain,and the strain resistant to Nisin was screened out.The growth curve,acid production,initial p H value,temperature tolerance,salinity tolerance,Acidity and other growth characteristics and fermentation performance of the study,the use of modern breeding methods to select anti-Nisin strains,the required lactic acid bacteria can tolerate a certain concentration of Nisin,so that the addition of Nisin both inhibit the growth of bacteria,and not Hinder the successful completion of fermentation.In this study,five strains of Lactobacillus bulgaricus HDSN-1 to HDSN-5 were isolated from commercially available yoghurt;one strain of Streptococcus thermophilus HDSN-6,Lactobacillus plantarum,HDSN-7,Lactobacillus acidophilus HDSN-8,Bifidobacterium lactis HDSN-9,1 Lactobacillus paracasei and Cheese Milk And the strain number was HDSN-10 and HDSN-11,respectively.The inhibition of Nisin in the range of 0 ? 1000IU/m L was determined by cup-dish method.The results showed that the minimum inhibitory concentration(MIC)of the five strains of L.bulgaricus was 250 IU/m L,one strain was 50 IU / m L,the MIC of S.thermophilus was 50 IU/m L,the MIC of L.acidophilus was 50 IU / m L The MIC of L.acidophilus was 5 IU/m L;the MIC of B.lactis was 10 IU/m L;and L.paracasei and L.casei had no inhibitory circle in this interval.According to the national standard,the most allowed Nisin A large number of 500 IU/m L,so the two bacteria for yogurt anti-Nisin lactic acid bacteria.At the same time,HDSN-1 was used to study the growth of five strains of L.bulgaricus,and HDSN-1 was used for the subsequent fermentation and yogurt test,because HDSN-1 had the advantages of good growth,fast acid production and low MIC value.HDSN-6,HDSN-7,HDSN-8 and HDSN-9 were screened by means of physical mutagenesis,chemical mutagenesis and complex mutagenesis.The excellent strains against Nisin were screened and their temperature Tolerance,salinity tolerance,initial p H test,and acidity determination.The results showed that the mutant lactic acid bacteria could not only be able to fermented the lactic acid bacteria,but also the lactic acid bacteria Tolerate a certain concentration of Nisin,but also retain the advantages of bacteria to ensure a smooth fermentation without affecting the results of fermentation. |
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