FIELD: chemistry.
SUBSTANCE: nisin A resistant Lactobacillus helveticus mutants are pre-extracted in concentration of 25-100 mcg/ml after culturing in MRS broth and MRS agar with nisin A. The extracted nisin-resistant mutants are re-cultured in MRS broth at pH 2, and then seeded on MRS agar with pH 5.7, incubated for 48 hours and survival rate thereof is determined. Acid-resistant Lactobacillus helveticus strains whose survival rate increases by more than 1.58 orders compared to the starting culture of Lactobacillus helveticus are extracted.
EFFECT: simple extraction procedure and high selectivity of extraction.
3 ex
