Formation of Viable but Non-culturable State of Cronobacter sakazakii during Milk Fermention
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Abstract:
In this study, Lactobacillus bulgaricus, a commonly used milk starter, was selected for milk fermentation. The interactions between C. sakazakii and Lactobacillus bulgaricus and the survival of C. sakazakii were investigated during milk fermentation. Furthermore, 16s rDNA high-throughput sequencing technique and PMA-qPCR method were used to analyze whether C. sakazakii entered into the viable but non-culturable (VBNC) state during milk fermentation. The results showed that after 48 h-fermentation of L. bulgaricus in milk, the values of pH and acidity reached to 3.40 and 212.00, respectively. When C. sakazakii was inoculated in milk in the middle fermentation stage, the pH value and acidity value were 3.47 and 214.30 respectively. When C. sakazakii was inoculated in milk in the early fermentation stage, the values of pH and acidity were 3.50 and 193.30 respectively after 48 h fermentation; which had a greater adverse impact on the fermentation. The concentration of C. sakazakii stabilized at 9.08 lg(CFU/mL) after 48 hours of growth in milk, the growth of C. sakazakii could not be detected by plate counting in the later stage of fermentation whenever C. sakazakii was inoculated into the milk. However, the existence of viable C. sakazakii could be detected by 16s rDNA and PMA-qPCR technology, which indicated that C. sakazakii could be VBNC state during milk fermentation. The existence of VBNC state of C. sakazakii might lead to an underestimation of total viable pathogenic cells, thus causing potential health hazards of milk and dairy products.
