Microgreen seed decontamination: Efficacy of hydrogen peroxide, hydrogen peroxide-peroxyacetic acid, and dry heat against Listeria monocytogenes

Microgreens, tender young greens cultivated from various seeds, are gaining popularity as a specialty crop grown indoors, primarily by small-scale growers. While the microgreens market is expanding rapidly, recalls due to Listeria monocytogenes contamination have become a concern. Since contaminated seeds are a primary source of pathogen introduction, this study evaluated seed decontamination methods involving soaking and heat treatments for borage and carrot microgreen seeds. Microgreen seeds were initially inoculated with L. monocytogenes by dipping, resulting in contamination levels of 5.0 ± 0.5 log CFU/g for borage seeds and 6.3 ± 1.1 log CFU/g for carrot seeds. The inoculated seeds were then subjected to various treatments: a 10-min soak in sterile deionized water (SDW), 3% hydrogen peroxide (H 2 O 2 ), or a combination of hydrogen peroxide and peroxyacetic acid (H-PAA), with or without subsequent heat treatment at 60 °C for 20 h. Results showed that the combination of H-PAA and heat treatment achieved the highest reductions in L. monocytogenes , with reductions of approximately 2.4 log in borage seeds and 3.3 log in carrot seeds. These reductions were significantly greater than those observed with heat alone or SDW soaking ( p < 0.05). Furthermore, L. monocytogenes levels in treated seeds remained significantly lower than untreated seeds throughout 10 weeks of storage at 4 °C ( p < 0.05). Importantly, the decontamination treatments did not adversely affect seed germination rates. This study provides scientifically validated strategies for mitigating L. monocytogenes contamination in microgreen seeds, offering practical benefits for home and small-scale farmers. • H-PAA and dry heat at 60 °C reduced Listeria monocytogenes by ≈2-3 log on carrot and borage microgreen seeds. • The reductions on carrot seeds were maintained during 10 weeks of storage at 4 °C. • Germination rates were not significantly reduced by the treatments.