Assessing water-assisted UV-C light and its combination with peroxyacetic acid and Pseudomonas graminis CPA-7 for the inactivation and inhibition of Listeria monocytogenes and Salmonella enterica in fresh-cut 'Iceberg' lettuce and baby spinach leaves

Abstract

The effectiveness of ultraviolet C light (UV-C) delivered in water (WUV) or in peroxyacetic acid (PAA) for theinactivation and inhibition ofL. monocytogenesandS. entericain ready-to-eat'Iceberg lettuce'and baby spinachleaves, was evaluated throughout chilled storage in modified atmosphere packaging (MAP). The inhibition ofpathogen's growth by sequential pretreatments with UV-C in PAA and then biocontrol usingPseudomonas gra-minisCPA-7 was assessed during MAP storage at 5 °C and upon a breakage of the cold-storage chain. In fresh-cutlettuce, 0 1 kJ/m2UV-C, in water or in 40 mg/L PAA, inactivated both pathogens by up to 2.1 ± 0.7 log10,which improved the efficacy of water-washing by up to 1.9 log10and showed bacteriostatic effects on bothpathogens. In baby spinach leaves, the combination of 0 3 kJ/m2UV-C and 40 mg/L PAA reducedS. entericaandL. monocytogenespopulations by 1.4 ± 0.2 and 2.2 ± 0.3 log10respectively, which improved water-washing by0.8 ± 0.2 log10. Combined treatments (0.1 or 0 3 kJ/m2WUV and 40 mg/L PAA) inactivated both pathogens inthe process solution from lettuce or spinach single sanitation, respectively. Pretreating lettuce with UV-C in PAAreducedL. monocytogenesandS. enterica's growth by up to 0.9 ± 0.1 log10with respect to the PAA-pretreatedcontrol after 6 d at 5 °C in MAP. Upon a cold-chain breakage, CPA-7 preventedS. entericagrowth in PAA-pretreated lettuce, whereas showed no effect onL. monocytogenesin any of both matrices. Low-dose UV-C in PAAis a suitable preservation strategy for improving the safety of ready-to-eat leafy greens and reducing the risk ofcross contamination.

This work has been supported the CERCA Programme / Generalitat de Catalunya, Spain; the Secretaria d'Universitats i Recerca del Departament d'Economia i Coneixement / Generalitat de Catalunya; the European Social Fund (grant FI-DGR-2015-0004); and the Spanish Ministry of Economy, Industry, and Competitiveness (National Project of the Spanish Foundation for Science and Technology: FECYT CC/2013105 (2013-16) and grant: RYC-2016-19949). Thanks are given to Marina Anguera for her technical assistance.