Influence of Sucrose Content on the Survival of Salmonella in Low-water Activity Whey Protein Model Systems at 70°C

Introduction: Salmonella spp. contamination has been and continues to be problematic within the food industry. Numerous Salmonella spp. outbreaks have been associated with low-water activity foods. Many products recalled for Salmonella contamination contain sugar. However, little is known about the effect of sugar on survival of Salmonella in foods at low-water activity.

Purpose: The purpose of this study was to determine if sucrose content of low-water activity protein powder affects the survival of various Salmonella species independently of water activity.

Methods: A four strain cocktail, S. Typhimurium, S. Tennessee, S. Agona, and S. Montevideo, was dried and added to whey protein powder that contained concentrations of 0, 5, and 20% (w/w) sucrose. Samples were equilibrated to the targeted water activity level before inoculation. Inoculated samples were treated at 70°C for 48 hours with samples tested for survivors at various times. Salmonella were recovered from treated samples using supplemented tryptic soy agar. Log values of survivors at different sugar contents and times were compared using ANOVA.

Results: Sugar content had no effect on survival of Salmonella in the lowest water activity samples (a_w 0.18). These treatments produced a decline in the Salmonella population from 10⁹ CFU/g to log reductions of 2.9 for 0%, 3.5 for 5%, and 2.3 for 20% sucrose samples over 48 hours. A protective effect of sucrose was observed at a_w 0.52 after 4 hours of heat treatment. This treatment achieved an average log reduction of 3.2 for samples containing 0 and 5% sucrose and a 2.3 log reduction for samples containing 20% sucrose.

Significance: The data suggests that effects of sucrose content in dry food on the survival of Salmonella during heat treatment are determined primarily by water activity. This observation will assist in the development of predictive models.