Influence of water activity on the heat resistance of Salmonella enterica in selected low-moisture foods

Bina Gautam; Byju N Govindan; Michael Gӓnzle; M S Roopesh

doi:10.1016/j.ijfoodmicro.2020.108813

Influence of water activity on the heat resistance of Salmonella enterica in selected low-moisture foods

Int J Food Microbiol. 2020 Dec 2:334:108813. doi: 10.1016/j.ijfoodmicro.2020.108813. Epub 2020 Aug 3.

Authors

Bina Gautam¹, Byju N Govindan², Michael Gӓnzle¹, M S Roopesh³

Affiliations

¹ Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta T6G 2P5, Canada.
² Department of Entomology, University of Minnesota, 1980 Folwell Avenue, 219 Hodson Hall, St. Paul, MN 55108, USA.
³ Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta T6G 2P5, Canada. Electronic address: roopeshms@ualberta.ca.

PMID: 32841809
DOI: 10.1016/j.ijfoodmicro.2020.108813

Abstract

Low-moisture foods (LMF with water activity, a_w < 0.85) including pet foods and black pepper powder have consistently been associated with foodborne disease caused by Salmonella enterica. Increased heat resistance and prolonged survival at low-moisture conditions, however, remain major challenges to achieve effective inactivation of Salmonella in low-moisture foods. At low water activity (a_w) conditions, heat resistance of Salmonella is greatly enhanced when compared to high a_w conditions. This study aimed to quantify the effect of a_w on the heat resistance of Salmonella enterica in pet food pellets and black pepper powder. Pet food pellets were inoculated with two strains of heat resistant S. enterica and black pepper powder was inoculated with a 5-strain cocktail of Salmonella. Both inoculated food samples were equilibrated at 0.33, 0.54, and 0.75 a_w in controlled humidity chambers. Inoculated pet food pellets and black pepper powder in closed aluminum cells were heat treated at specific temperatures for selected times. The results showed that the Weibull model fitted well the inactivation data. At a specific temperature, the rate of inactivation increased with the increase in the a_w from 0.33 to 0.75, and the 3-log reduction times decreased for Salmonella in both food samples with the increase in a_w. Water adsorption isotherms of pet food pellets and black pepper powder at initial and treatment temperatures were developed to understand the change in a_w during heat treatments. The change in a_w during heat treatment was dependent on the type of food matrix, which possibly influenced the thermal inactivation of Salmonella in pet food pellets and black pepper powder. The quantitative analysis of heat reduction of Salmonella with respect to a_w aids in selection of the appropriate initial a_w to develop effective heat treatment protocols for adequate reduction of Salmonella in pet foods and black pepper powder.

Keywords: Black pepper powder; Heat treatment; Pet foods; Water activity; Water sorption isotherm; Weibull model.

MeSH terms

Animal Feed / analysis
Animal Feed / microbiology
Colony Count, Microbial
Food Microbiology
Hot Temperature*
Pasteurization / methods*
Salmonella enterica / physiology*
Spices / analysis
Spices / microbiology
Water* / analysis

Substances

Water