Abstract: The effects of levulinic acid, L-lactic acid, acetic acid and hydrochloric acid at pH 6.0 and 5.4 on the acid tolerance response of Salmonella typhimurium and S. Derby were investigated. The results showed that the bacteriostatic effects of the four acids were in the following decreasing order: levulinic acid > acetic acid > L-lactic acid > hydrochloric acid. Significantly higher acid tolerance response was induced in Salmonella at pH 5.4 than at pH 6.0 (P < 0.05). The acid tolerance induced by levulinic acid was weaker when compared with the two other organic acids and significantly varied with pH (P < 0.05). The intracellular pH of Salmonella treated with the organic acids was significantly different from that of the control group, and the intracellular pH of S. typhimurium treated with levulinic acid at pH 6.0 was significantly higher than that of S. Derby receiving the same treatment (P < 0.05). The results showed that acidic conditions at pH 6.0 and 5.4 could induce acid tolerance in Salmonella, and the change of intracellular pH was closely related to the acid tolerance response.

Key words: Salmonella, acid tolerance response, organic acids, intracellular pH, food safety