Validation of E. faeciumNRRL B-2354 as a surrogate for Listeria on apples during cold storage and gaseous ozone treatments.

Listeria monocytogenes poses a serious food safety risk due to its ability to survive and grow on produce during cold storage. This study evaluates Enterococcus faecium NRRL B-2354 as a non-pathogenic surrogate for L. monocytogenes during up to 24 weeks of simulated lab storage and 36 weeks of commercial storage, including refrigerated air (RA), controlled atmosphere (CA), CA with 1-methylcyclopropene (1-MCP), with or without gaseous ozone treatment. Results indicate that E. faecium exhibited die-off patterns comparable to L. monocytogenes, with 2.5-2.7 log CFU/apple reduction during 18 weeks of ambient storage, 2.7-2.8 log reduction over 24 weeks at 4 °C, and 3.4-3.5 log reduction after 36 weeks of RA and CA storage. E. faecium exhibited greater stability under CA storage with ozone treatment. These findings suggest that E. faecium NRRL B-2354 is a suitable surrogate for L. monocytogenes in cold storage environments. A 24-week low-dose continuous gaseous ozone application followed by 12 weeks of CA storage resulted in ∼ 5 log CFU/apple reduction of Listeria, reflecting both the treatment effects and natural die-off under CA storage. These results demonstrate gaseous ozone as a viable intervention strategy as a Listeria control during commercial storage and support the use of E. faecium NRRL B-2354 in validating cold storage practices.