Modeling the Effect of Temperature and Water Activity on the Thermal Resistance of Salmonella Enteritidis PT 30 in Wheat Flour

Abstract

Salmonella continues to be a problem associated with low-moisture foods, particularly given enhanced thermal resistance at lower water activity (a). However, there is a scarcity of thermal inactivation models accounting for the effect of a. The objective of this study was to test multiple secondary models for the effect of product (wheat flour) a on Salmonella enterica Enteritidis phage type 30 thermal resistance. A full-factorial experimental design included three temperatures (75, 80, and 85°C) and four a values (~0.30, 0.45, 0.60, and 0.70). Prior to isothermal treatment, sample a was achieved by equilibrating samples in a humidity-controlled conditioning chamber. Two primary models (log linear and Weibull type) and three secondary models (second-order response surface, modified Bigelow type, and combined effects) were evaluated using the corrected Akaike information criterion and root mean squared errors. Statistical analyses of the primary models favored the log-linear model. Incorporating the three secondary models into the log-linear primary model yielded root mean squared errors of 2.1, 0.78, and 0.96 log CFU/g and corrected Akaike information criterion values of 460, -145, and -19 for the response surface, modified Bigelow, and combined-effects models, respectively. The modified Bigelow-type model, which exponentially scaled both temperature and a effects on thermal inactivation rates, predicted Salmonella lethality significantly better (P < 0.05) than did the other secondary models examined. Overall, a is a critical factor affecting thermal inactivation of Salmonella in low-moisture products and should be appropriately included in thermal inactivation models for these types of systems.

Inoculation Protocols Influence the Thermal Resistance of Salmonella Enteritidis PT 30 in Fabricated Almond, Wheat, and Date Products

“…For the postfabrication results, the same general rank ordering was true (P , 0.05), except for a smaller difference between almond and wheat products. This observation is consistent with prior Salmonella Enteritidis PT 30 studies, which have reported larger D-values for high fat products (e.g., D 838C of 16 min for peanut butter (16) compared with a D 808C of 5 min for wheat flour (22)).…”

“…According to Smith et al (22), Salmonella Enteritidis PT 30, which was inoculated via a method similar to the present postfabrication protocol, exhibited a D 808C of 5.5 min in wheat flour at 0.43 a w , which was lower than that for postinoculation wheat flour at 0.4 a w (15.1 min). Smith et al (22) used commercial white wheat flour, which may have altered the heat resistance because of differences in composition (i.e., lower lipids content) and particle-cell interactions. Syamaladevi et al (24) also assessed thermal inactivation of a Salmonella cocktail in wheat flour at 808C (inoculated postfabrication).…”

Dry inoculation methods for nonfat milk powder

“…The z values of SiO 2 -Salmonella, SiO 2 -E. faecium, and NFMP-Salmonella in NFMP at a w = 0.25 ± 0.02 varied from 16.0 to 16.5°C. These data match previously reported z values of Salmonella Enteritidis (16.9°C) and E. faecium (16.2°C) in wheat flour at a w = 0.30 ± 0.02 (Liu et al, 2018) and those of Salmonella Enteritidis in wheat flour (16.7 ± 0.73°C) modeled from D-values at 75 to 85°C at a w = 0.31-0.70 (Smith et al, 2016). From reported data, z values of both strain sets might be independent of inert carriers (NFMP or SiO 2 ) and food matrices.…”

Long-Term Survival and Thermal Death Kinetics of Enterohemorrhagic Escherichia coli Serogroups O26, O103, O111, and O157 in Wheat Flour

“…Smith et al reported D values of 9.97, 5.51, and 2.11 min at 75, 80, and 85°C for Salmonella enterica Enteritidis PT 30 in wheat flour (a w , 0.43). They also reported ␦ values of 8.08, 4.97, and 1.59 min for the same temperatures (48). In another study, a D 80 value of 6.9 min for Salmonella in all-purpose wheat flour with a w of 0.45 was reported (49).…”

“…In the present study, the EHEC's D, ␦, and Z values were smaller than those previously reported for Salmonella, but they were still considerably higher than those for E. coli in many other types of matrices, including foods with higher a w . A closed system using 0.5-ml PCR tubes was applied for thermal treatment procedures preventing changes in a w decrease during the process, which may inversely affect the thermal death kinetics calculations (48,49).…”