Influence of Water Activity on Thermal Resistance of Salmonella enterica and Quality changes in Low-moisture Foods

• Author / Creator

  Gautam, Bina

• Low-moisture foods (with aw < 0.85) including pet foods and black pepper powder have been associated with major recalls due to contamination by Salmonella spp. Increased thermal resistance and prolonged survival at low-moisture conditions are major challenges to achieve effective inactivation of Salmonella in low-moisture foods. At low water activity (aw) conditions, elevated temperatures or increased treatment times are generally required for achieving a required level of inactivation of Salmonella. The objective of this study was to evaluate the effect of aw on the thermal resistance of Salmonella enterica in pet food pellets and black pepper powder quantitatively, and the effect of thermal treatments on selected quality parameters of these food products. Non-contaminated pet food pellets were inoculated with two pure strains of heat resistant S. enterica and black pepper powder was inoculated with an additional three more strains of Salmonella. Both inoculated food samples were equilibrated at 0.33, 0.54, and 0.75 aw in controlled humidity chambers. Inoculated pet food pellets and black pepper powder in closed aluminum cells were thermally treated at specific temperatures for selected times. The observed log reductions in Salmonella population after thermal treatments were used to analyze the inactivation rate in both samples. The results showed that the inactivation was well fitted with the Weibull model. At a specific temperature, the rate of inactivation increased with the increase in the aw from 0.33 to 0.75, and the 5-log reduction times decreased for Salmonella in both food samples with higher aw. Water adsorption isotherms of pet food pellets and black pepper powder at initial and treatment temperatures were developed to understand the change in aw during thermal treatments. The similar TBARS values for control and treated samples for different aw samples presented no significant change in lipid oxidation after the thermal treatments. But the piperine level in 0.75 aw sample was significantly lower than any treated samples with 0.33 and 0.54 aw, except for 0.54 aw samples treated at 80ºC. The quantitative analysis of thermal reduction of Salmonella with respect to aw and quality analysis of heat-treated samples will help to select the appropriate initial aw to develop effective thermal treatment protocols for adequate reduction of Salmonella in pet foods and black pepper powder with minimal changes in quality parameters.

• Subjects / Keywords

  • Thermal resistance
  • Low-moisture foods
  • Salmonella
  • Pet food pellets
  • Black pepper powder
  • Water activity

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-a8gy-ms37

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.