酸馴化影響 Salmonella typhimurium 與 Bacillus cereus 在牛乳乳酸發酵及產品中之生長與存活

Abstract

In this study, Salmonella typhimurium and Bacillus cereus were subjected to acid adaptation at pH 5.5 for 1-4 h and pH 6.3 for 40-90 min, respectively. Effect of acid adaptation on the acid tolerance of Sal. typhimurium and B. cereus at pH 4.0 and 4.6, respectively, was first examined. Furthermore, growth and survival behavior of these pathogens during the lactic fermentation of skim milk by Streptococcus thermophilus or Lactobacillus bulgaricus and during the 10-day storage of laboratory-prepared and commercial dairy lactic fermented products at 5 ℃ were also investigated. It was found that the acid adaptation, regardless the adaptation time, increased the acid tolerance of test organisms. The highest enhanced effect was noted for Sal. thphimurium and B. cereus after subjected to acid adaptation for 4 h and 40 min, respectively. During the lactic fermentation of skim milk, survival of acid-adapted cells of Sal. typhimurium and B. cereus was higher than the non-adapted cells. Similar phenomenon was also noted during the storage of laboratory-prepared and commercial lactic fermented product at 5 ℃. While acid-adapted cells of B. cereus showed a less magnitude of enhanced acid tolerance in the commercial lactic fermented products of milk during the storage period. In addition, acid adaptation may also enhance the tolerance of Sal. thphimurium and B. cereus to refrigerated temperature and other antimicrobial principles in fermented milk.