Use of caprylic acid to control pathogens (Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium) in apple juice at mild heat temperature

Aims: The aim of this study was to examine the effects of caprylic acid (CA) on pathogens in apple juice having intrinsic organic acids, and to determine any synergistic effects. Methods and Results: Bactericidal effects of CA were examined against Escherichia coli O157:H7 and Salmonella Typhimurium present in apple juice at mild heating temperatures. Apple juice containing each of the pathogens was treated with CA (0·1, 0·2, 0·4, 0·6 or 0·8mmoll^-1) at 50 or 55°C. Treatment with 0·8mmoll^-1 (0·013%) CA at 50°C for 5min or with 0·6mmoll^-1 (0·010%) CA at 55°C for 5min resulted in the complete eradication of E.coli O157:H7 (initial population: 7·25-7·34logCFUml^-1). Salmonella Typhimurium were more sensitive than E.coli O157:H7: all bacteria (7·81-7·55logCFUml^-1) were eradicated by treatment with 0·2mmoll^-1 (0·0032%) CA at 55°C for 5min or with 0·6mmoll^-1 CA at 50°C for 5min. By contrast, when pH-adjusted apple juice (pH 7·0) was treated with 0·8mmoll^-1 CA, there was no significant difference in bactericidal effects between CA-treated samples and controls (heat treatment alone or heat+0·1% ethanol treatment). This result suggested that acidic pH in the apple juice boost the antibacterial effects of CA. CA treatment did not affect (P>0·05) the pH, colour or °Brix of the apple juice. Conclusion: This study highlights the utility of CA as a natural antibacterial agent that can eliminate micro-organisms from apple juice at very low concentrations (≤0·013%) and temperatures (≤55°C) within a short time (≤10min). Significance and Impact of the study: The results of our study may contribute to the development of an efficient method for improving the microbiological safety of apple juice.