Combined effects of heat, acetic acid, and salt for inactivating Escherichia coli O157:H7 in laboratory media

Heat, acid, and salt have been commonly used to ensure the microbial safety of foods and are often used in combinations in many food products. When combined, they can produce different results, such as additive, synergistic, and antagonistic effects. However, there has been little investigation into the effect of these combination treatments. Therefore, in this study, the effect of combined treatment of heat, acid, and salt was investigated in laboratory media. All possible paired combinations among three factors, heat (55 °C), acid (0.25% acetic acid, [v/v]) and salt (3%, [w/v]) were tested and compared with individual treatments for killing E. coli O157:H7 in laboratory media. When salt was combined with heat, there was no significant difference in reduction of E. coli O157:H7 (additive effect). However, when acid was combined with heat, there was a higher reduction of E. coli O157:H7 (synergistic effect). When salt was combined with acid treatment, salt gave protection against acid treatment (antagonistic effect), thus, there was lower reduction of E. coli O157:H7 in the combined treatment than in the single acid treatment. Depending on the combination of preserving factors, results were different.