A novel technique using ozone micro bubbles to control microbial contamination and browning of fresh-cut lettuce

Fresh-cut lettuce has become popular among consumers. However an increased number of food safety outbreaks associated with fresh-cut produce require investigations into novel microbial decontamination methods infresh-cut lettuce products. This study investigated the effects of a novel technique using ozone micro bubbles (O₃-MBs) on microbial control and quality of fresh-cut 'Cos' lettuce. Fresh-cut 'Cos' lettuce leaves were washed in O₃-MBs (~0.5 ppm) for 5 min at ambient temperature and compared with chlorinated water (NaOCl, 100 mg L^-1, 5 min). For total bacteria counts, coliform counts and yeast and mould, O₃-MBs treatment resulted into a 1-2 log reduction, which was similar to the result achieved by 100 mg L^-1 chlorinated water. The amount of phenolic compounds of the lettuce was reduced by O₃-MBs treatments. Washing with O₃-MBs also inhibited PPO activity for up to six days of storage at 4°C which is correlated with a lower amount of quinone content during storage. An inhibitory effect of browning enzyme and substrate resulted in a lower browning symptom of fresh-cut lettuce during storage. These results indicate that O₃-MBs could be an alternative sanitizer to chlorine for fresh-cut lettuce due to a bacterial inhibitory effect and retention of sensorial quality and browning control.