Effect of acid adaptation on the resistance of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium to X-ray irradiation in apple juice

Abstract

This study aimed to investigate the effect of acid adaptation on the resistance of Escherichia coli O157:H7 and Salmonella Typhimurium to X-ray irradiation. The non-acid-adapted and acid-adapted E. coli O157:H7 cell counts decreased 8.02 and 5.48 log CFU/mL in apple juice, respectively, whereas the S. Typhimurium cell counts reduced by 3.87 and 3.98 log CFU/mL, respectively, after treatment with 1.0 kGy X-ray. In apple juice, the D5d (dose required for 5-log reduction in cell count) values for non-acid-adapted and acid-adapted E. coli O157:H7 cells were 0.66 and 0.92 kGy, respectively, whereas those for non-acid-adapted and acid-adapted S. Typhimurium cells were 1.40 and 1.30 kGy, respectively. The acid-adapted E. coli O157:H7 cells exhibited higher X-ray resistance than the non-acid-adapted cells in apple juice. However, the acid-adapted and non-acid-adapted S. Typhimurium cells exhibited similar resistance to X-ray irradiation in apple juice. Additionally, the effect of X-ray irradiation on apple juice quality attributes was evaluated. The color, pH, and total phenolic contents of apple juice were not significantly affected (P > 0.05) at all treatment doses of X-ray. The results of this study suggest that the inactivation of acid-adapted cells of E. coli O157:H7, which is the predominant pathogen implicated in apple juice-related disease outbreaks, must be considered for the application of X-ray irradiation in apple juice sterilization process.