Optimisation of the combined treatment of nisin, oregano and ultrasound in decontaminating Listeria monocytogenes and Escherichia coli O157:H7 on cabbage

Abstract

The effect of combined nisin, oregano and ultrasound treatments on the reduction of Listeria monocytogenes and Escherichia coli O157:H7 on raw cabbage was investigated using Box-Behnken response surface design. The optimised treatment comprising oregano (0.20% v/v), nisin (607.85 IU/g) and ultrasound treatment (14.98 min) showed the highest log reduction of E. coli O157:H7 (3.66 CFU/mL) on cabbage. For L. monocytogenes, an optimal combination of oregano (0.12% v/v), nisin (731.25 IU/g) and ultrasound (13.21 min) resulted in the highest log reduction (8.27 CFU/mL). SEM images showed the effectiveness of the combination treatments against the studied pathogens. The physical properties (colour and texture) of cabbage were analysed after treatment, while the structural damage was determined by electrolyte leakage analysis. There were no colour and textural changes observed between untreated and treated cabbage, while the electrolyte leakage rate increased slightly after application with the combination treatments. The results demonstrate that combined use of oregano, nisin and ultrasound is a promising alternative for E. coli O157:H7 and L. monocytogenes reduction and retaining of the quality characteristics of fresh produce.