Assessment of trans-cinnamaldehyde and eugenol assisted heat treatment against Salmonella Typhimurium in low moisture food components.

Increased thermal resistance of Salmonella at low water activity (a) is a significant food safety concern in low-moisture foods (LMFs). We evaluated whether trans-cinnamaldehyde (CA, 1000 ppm) and eugenol (EG, 1000 ppm), which can accelerate thermal inactivation of Salmonella Typhimurium in water, can show similar effect in bacteria adapted to low a in different LMF components. Although CA and EG significantly accelerated thermal inactivation (55 °C) of S. Typhimurium in whey protein (WP), corn starch (CS) and peanut oil (PO) at 0.9 a, such effect was not observed in bacteria adapted to lower a (0.4). The matrix effect on bacterial thermal resistance was observed at 0.9 a, which was ranked as WP > PO > CS. The effect of heat treatment with CA or EG on bacterial metabolic activity was also partially dependent on the food matrix. Bacteria adapted to lower a had lower membrane fluidity and unsaturated to saturated fatty acids ratio, suggesting that bacteria at low a can change its membrane composition to increase its rigidity, thus increasing resistance against the combined treatments. This study demonstrates the effect of a and food components on the antimicrobials-assisted heat treatment in LMF and provides an insight into the resistance mechanism.