Effect of Challenge Temperature and Solute Type on Heat Tolerance of Salmonella Serovars at Low Water Activity

Abstract

Salmonella spp. are reported to have an increased heat tolerance at low water activity (a w ; measured by relative vapor pressure [rvp]), achieved either by drying or by incorporating solutes. Much of the published data, however, cover only a narrow treatment range and have been analyzed by assuming first-order death kinetics. In this study, the death of Salmonella enterica serovar Typhimurium DT104 when exposed to 54 combinations of temperature (55 to 80°C) and a w (rvp 0.65 to 0.90, reduced using glucose-fructose) was investigated. The Weibull model (LogS ‫؍‬ ؊bt n ) was used to describe microbial inactivation, and surface response models were developed to predict death rates for serovar Typhimurium at all points within the design surface. The models were evaluated with data generated by using six different Salmonella strains in place of serovar Typhimurium DT104 strain 30, two different solutes in place of glucose-fructose to reduce a w , or six low-a w foods artificially contaminated with Salmonella in place of the sugar broths. The data demonstrate that, at temperatures of >70°C, Salmonella cells at low a w were more heat tolerant than those at a higher a w but below 65°C the reverse was true. The same patterns were generated when sucrose (rvp 0.80 compared with 0.90) or NaCl (0.75 compared with 0.90) was used to reduce a w , but the extent of the protection afforded varied with solute type. The predictions of thermal death rates in the low-a w foods were usually fail-safe, but the few exceptions highlight the importance of validating models with specific foods that may have additional factors affecting survival.

Effect of Desiccation on Tolerance of Salmonella enterica to Multiple Stresses

“…Using laboratory models, it was demonstrated that reducing water activity either by desiccation (24,31) or by addition of solutes (2,12,30,37,38) resulted in increased thermal tolerance. Furthermore, low-water-activity medium (30) and dry environment (24) were found to enhance Salmonella tolerance to sodium hypochlorite and ethanol, respectively.…”

Enhancement of enterohemorrhagic Escherichia�coli O157:H7 stress tolerance via pre-heating

“…Hernandez et al reported on the stress response of Staphylococcus aureus (17), but there are few reports on the stress response and tolerance of bacteria that cause food poisoning (18). In particular, there are only a few reports of the thermotolerance of enterohemorrhagic E. coli (19).…”

Challenges in the Control of Foodborne Pathogens in Low-Water Activity Foods and Spices

“…Salmonella is widespread in nature and survives in dry foods for weeks, months, or even years (Chang et al 2013 ;Beuchat and Mann 2010a ;Komitopoulou and Peñaloza 2009 ;Beuchat and Scouten 2002 ;Burnett et al 2000 ;Archer et al 1998 ). Food composition, water activity, and temperature collectively infl uence its survival in foods (He et al 2011 ;Mattick et al 2001 ;Corry 1974 ;Dega et al 1972 ;Moats et al 1971 ). The pathogen exhibits increasing resistance at decreasing water activity during heat treatment (Beuchat and Scouten 2002 ;Doyle and Mazzotta 2000 ;Archer et al 1998 ).…”