Effects of a novel combination of gallic acid, hydrogen peroxide and lactic acid on pathogen inactivation and shelf-life of baby spinach

Recurring foodborne illness outbreaks associated with the consumption of contaminated leafy greens attest to the challenges facing the produce industry. Here we report the effects of a novel combination of gallic acid (1500 mg/L), hydrogen peroxide (30 mg/L), and lactic acid (1800 mg/L) (GHL) on inactivation of foodborne human pathogens on baby spinach. Fresh baby spinach samples inoculated with Escherichia coli O157:H7 and Listeria monocytogenes were treated with the GHL formulation, chlorine (50 mg/L), peroxyacetic acid (80 mg/L), water, or remained unwashed. E. coli O157:H7 and L. monocytogenes populations on baby spinach and product quality and shelf-life were determined following treatments on processing day and during cold storage for up to 14 days. Washing baby spinach with GHL for 2 min reduced E. coli O157:H7 by 0.9 Log CFU/g while washing with chlorine and peroxyacetic acid reduced E. coli O157:H7 by 0.6 Log CFU/g. E. coli O157:H7 populations declined over time during cold storage in all treatment groups. However, GHL-treated samples maintained significantly lower E. coli O157:H7 populations throughout the storage period. On the other hand, all treated samples showed significantly reduced L. monocytogenes populations compared to water washed samples, while no significant difference was observed among GHL, chlorine, and peroxyacetic acid treatments. L. monocytogenes grew during storage and the difference in populations among all treatments was not significant. GHL washed samples showed slight browning (6 on a scale of 100) on rib edges and injured leaf surfaces, which disappeared within three days during storage. No other significant quality difference was observed among treatments. The results suggest that GHL can serve as an alternative to conventional sanitizers for fresh produce washing. GHL could be especially useful for the organic produce industry where the application of chlorine is limited.

Automated summary

This study reports the effectiveness of a novel combination, GHL, in eliminating foodborne pathogens in baby spinach. Compared to chlorine and peroxyacetic acid, GHL showed better efficacy in reducing E. coli O157:H7 populations and maintaining lower levels during cold storage. All treatments effectively reduced L. monocytogenes populations, with minimal differences observed during storage.