Abstract
With more ready-to-eat foods and increased shelf-lives, prevention of Listeria monocytogenes contamination has become a necessity for the food industry. This study examined the effects of sublethal heat treatment on the decimal reduction time (D-values) of three L. monocytogenes serotypes (1/2a, 1/2b, 4c), and non-pathogenic L. innocua. The D70 (D-value at 70℃) values of heat-shocked (HS) and non-heat-shocked (NHS) Listeria grown in tryptic soy broth (TSB) were determined. The D70 values of HS L. monocytogenes serotype 1/2a and L. innocua were significantly higher compared to NHS cultures, although by 48 h, the values returned to NHS levels. When HS and NHS 1/2a and 1/2b were inoculated on crab meat and cooked shrimp, the D70 values of HS cultures were at least 2-fold higher, compared to when they were grown in TSB. This increase in heat resistance for the HS cultures may be attributed to the protective effect of the seafood matrix itself.
Highlights
In the past several decades, listeriosis, caused by the intracellular pathogen Listeria monocytogenes, has emerged as a major foodborne disease worldwide [1]-[3]
Heat shocking significantly increased the D70-values of L. monocytogenes 1/2a and L. innocua on day 0 (Table 1), but not that of L. monocytogenes 1/2b and 4c
The D-value reversion findings suggest that heat shocked L. monocytogenes cultures have the ability to recover from non-lethal heat treatments after 24 h once recultured into fresh enrichment broth
Summary
In the past several decades, listeriosis, caused by the intracellular pathogen Listeria monocytogenes, has emerged as a major foodborne disease worldwide [1]-[3]. Of the eight current species in the genus Listeria, L. monocytogenes is the only one considered to be a foodborne pathogen in both humans and animals [4]. Lineages I and II are both associated with human disease, most human listeriosis isolates are from lineage I. Lineage II strains are more frequently associated with sporadic listeriosis in humans, but are associated with animal listeriosis. Lineage III and IV isolates are rarely found in foods or food-related environments, and have not been linked to human listeriosis [5]. Serovars 1/2a (lineage II), 1/2b and 4b (lineage I) account for 95% of human isolates [6]
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