Combined effect of mild heat and acetic acid treatment for inactivating Escherichia coli O157:H7, Listeria monocytogenes and Salmonella typhimurium in an asparagus puree

AIMS: This study was conducted to validate combined heat and acid treatments for inactivating Escherichia coli O157:H7, Listeria monocytogenes and Salmonella typhimurium in an acidified brine containing, or pickled, asparagus model food. METHODS AND RESULTS: A mixture of three strains of E. coli O157:H7, L. monocytogenes and S. typhimurium were inoculated onto pickled asparagus samples. Combinations of various concentrations of acetic acid [0%, 0.25%, 0.5%, 0.75%, 1%, 1.5% and 2% (v/v)] and various temperatures (40 degrees C, 50 degrees C, 60 degrees C and 75 degrees C) were investigated. Following treatment, asparagus samples were stored at room temperature and enumerated at 0, 0.5, 1, 2 and 3 days. Heat and acetic acid treatments were synergistic. The inhibitory effects of these combined treatments on the tested foodborne pathogens were also effective during storage. Loss of green colour in the pickled asparagus significantly increased with increasing concentrations of acetic acid. CONCLUSIONS: Using a combination of mild heat and acetic acid treatments can successfully control E. coli O157:H7, L. monocytogenes and S. typhimurium in pickled asparagus, combinations of heat and acid are synergistic and effective treatments can be selected to reduce adverse effect on colour which occur during product storage. SIGNIFICANCE AND IMPACT OF THE STUDY: Mild heating plus acetic acid treatment are synergistic, so combined treatments can be developed, which would lower the temperature and amount of acetic acid required for minimally processed vegetables while maintaining pathogen control.