Viability of acid-adapted and non-adapted Bacillus cereus during the lactic fermentation of skim milk and product storage at 5°C

Abstract

In this study, Bacillus cereus was subjected to acid adaptation at pH 6.3 for 40 min. It was found that acid-adapted B. cereus exhibited a higher survival percentage than non-adapted cells after exposure to an acidic condition of pH 4.6. The viable population of both acid-adapted and non-adapted B. cereus increased during the first 12-18 hr of lactic fermentation of skim milk by Streptococcus thermophilus or Lactobacillus bulgaricus, and then declined as the fermentation extended. However, the acid-adapted cells exhibited a lower population reduction rate than the non-adapted B. cereus. A higher viable population of acid-adapted B. cereus than the non-adapted cells was also noted in Str. thermophilus-fermented skim milk and the two commercial lactic fermented products kept at 5°C. Additionally, the acid adaptation could reduce the susceptibility of B. cereus to acidity, refrigerated temperature and other detrimental principles present in lactic fermented milk products.