A total of 120 minimally processed, cut and packaged lettuce samples were purchased from retail supermarkets or provided by a salad production facility over an 8‐month period. The samples were tested for total aerobic plate counts and for the presence of potentially pathogenic species belonging to the genera of Listeria, Aeromonas and Yersinia. The aerobic plate counts ranged from 103 to 109 colony forming units (cfu) g−1. Most samples (76%) contained between 105 and 107 cfu g−1 total aerobic bacteria. Listeria monocytogenes was isolated from three samples, Aeromonas hydrophila or Aeromonas caviae from 66 samples, and Yersinia enterocolitica from 71 samples. The pathogenic potential of Y. enterocolitica isolates was determined by screening for an array of biochemical, serological and genetic traits (heat‐stable enterotoxin gene, the attachment and invasion gene locus, the invasin gene locus and the virulence plasmid). The Y. enterocolitica isolates lacked many of the phenotypic and genetic markers associated with virulence in primary pathogenic strains. As the roles of the reputed virulence factors of Aeromonas spp. in human infection are uncertain, the pathogenic potential of the Aeromonas isolates in lettuce remains unclear.
Aims: To determine the resistance of a variety of Bacillus species spores to a combined high pressure and heat treatment; and to determine the affect of varying sporulation and treatment conditions on the level of inactivation achieved. Methods and Results: Spores from eight Bacillus species (40 isolates) were high pressure–heat treated at 600 MPa, 1 min, initial temperature 72°C. The level of inactivation was broad (no inactivation to 6 log10 spores ml−1 reduction) and it varied within species. Different sporulation agar, high pressure equipment and pressure‐transmitting fluid significantly affected the response of some isolates. Varying the initial treatment temperature (75, 85 or 95°C) shifted the relative order of isolate high pressure–heat resistance. Conclusions: The response of Bacillus spores to combined high pressure–heat treatment is variable and can be attributed to both intrinsic and extrinsic factors. The combined process resulted in a high level of spore inactivation for several Bacillus species and is a potential alternative treatment to traditional heat‐only processes. Significance and Impact of the Study: Sporulation conditions, processing conditions and treatment temperature all affect the response of Bacillus spores to the combined treatment of high pressure and heat. High levels of spore inactivation can be achieved but the response is variable both within and between species.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.