Study On The State Change Of Salmonella During Tea Storage And Brewing

Salmonella is one of the most important food pathogens in the world.It causes severe foodborne diseases.More and more food has been reported as the medium of salmonellosis,including dry food,such as nuts and tea.Salmonella could turned into the viable but nonculturable(VBNC)state on dry food,remaining threats to public health and food safety due to the non-detectability through conventional plate counting technique.In this study,a new technique that combined the propidium monoazide and quantitative polymerase chain reaction(PMA-qPCR)was developed to detect Salmonella in VBNC state on teas.This technique was specific and sensitive with the detecting limitation of 102 CFU/g.PMA-qPCR and plate counting method were employed to detect Salmonella in culturable and VBNC state on the 4 kinds of artificially contaminated teas.Salmonella survived well on vacuum dried tea,in which 105-107 CFU/g culturable cells were detected after 120 days,when the initially bacterial load was 106 CFU/g.The result indicated that the temperature has the most effect on Salmonella during the storage of tea.Under 4℃ and 10℃,the number of culturable cells was comparable to initially inoculated,while it reduced by 2 orders of magnitude under 25℃.The number of culturable cells on the 4 teas changed significantly in the starting 10 days of storage,and then gradually tended to be stable,eventually no longer changed after 60 days.PMA-qPCR was applied to detect Salmonella at 25℃ after 60 days storage.The result indicated that most of the reduced culturable cells turned into VBNC state.This study also detected the Salmonella on the tea in different brewing methods.The results indicated that almost all bacteria survived in cold brew.Brewing at 75℃ for 10 min also didn’t kill all Salmonella.At least 70%of the survived bacteria probably turned into VBNC state.Instantly brewing just killed part of the cells even using 80℃ water.At least 80%of the survived bacteria turned into VBNC state.These results indicated that the risk of Salmonella contamination on the tea could not be eliminated by brewing.