Determination of thermal inactivation kinetics (D- and z-values) of Salmonella in brownie batter

Primary Author: Monipel Ansong

Faculty Sponsor: Minto Michael


Primary College/Unit: Agricultural, Human and Natural Resource Sciences

Category: Agricultural and Natural Resource Sciences

Campus: Pullman




Principal Topic: Salmonella can be introduced into bakery products through ingredients such as flour, milk, cocoa powders, and eggs. Studies have shown that Salmonella can survive under adverse environmental conditions over time; therefore, it is vital to study the thermal inactivation kinetics (D- and z-values) of Salmonella in bakery products such as brownie batter. The aim of this study was to determine the D- and z-values of a 5-serovar Salmonella cocktail in brownie batter.


Methods: All-purpose flour was inoculated with a 5-serovar Salmonella cocktail (Enteritidis, Senftenberg, Typhimurium, Montevideo and Newport) and used to prepare brownie batter. This study implemented a randomized complete block design with three replications as blocks. The batter was subjected to heat treatment using thermal-death-time disks in hot water bath at 64, 68, 72 and 76C for 0, 3, 6, 9, 12 min, respectively. The Salmonella population was enumerated using injury-recovery media (brain heart infusion agar overlaid with xylose lysine deoxycholate agar). The graphs for calculating D- and z-values were plotted using Microsoft Excel, and D- and z-values were calculated as absolute values of the inverse of slopes.


Results/implications: The D-values of 5-serovar Salmonella cocktail in brownie batter were 53.4±5.38, 27.2±2.04, 10.7±0.72 and 4.6±0.49 min at 64, 68, 72 and 76C, respectively; whereas, z-value of the Salmonella cocktail was 11.1±0.71C. D-values from this study provide the basic information about the thermal resistance of Salmonella in brownie batter at the start of baking and could help the bakery industry to optimize cooking parameters ensuring the safety of brownies.