Influence of Sucrose, Fructose, and Sorbitol on the Survival of Salmonella in a Low-water Activity Whey Protein Model System at 70°C

Introduction: In recent years, numerous Salmonella spp. outbreaks have been attributed to low a_w foods. Many of these food products recalled for Salmonella contain sugars. The impact of reducing sugar (fructose), non-reducing sugar (sucrose), and sugar alcohol (sorbitol) at low a_w levels (below a_w < 0.60) has yet to be determined.

Purpose: The purpose of this study was to determine if sugar in low a_w whey protein powder affects the survival of Salmonella independent of water activity at 70°C.

Methods: A four-strain cocktail, Salmonella Typhimurium, Tennessee, Agona, and Montevideo, was dried and added to either 0, 20, or 40% (w/w) sugar supplemented protein samples that were equilibrated to a_w of 0.20 ± 0.02, 0.42 ± 0.01, or 0.54 ± 0.01. Sugars tested included sucrose, fructose and sorbitol. After heat treatment (70°C for up to 48 h), survivors were enumerated using supplemented tryptic soy agar and data were analyzed using two-way ANOVA.

Results: After 48 h of heat treatment, log reduction at 40% sugar was significantly increased (P =  0.0042) by an average of 2.5 log units (a_w = 0.42) and 3 log units (a_w = 0.54) when fructose or sorbitol was added to the protein powder. Addition of fructose or sorbitol (20 or 40%) significantly (P < 0.0001) increased survival of Salmonella over 48 h of treatment. Overall, the water activity was a significant (P < 0.02) factor in survival when comparing both the types of sugar and the amount of sugar used per treatment.

Significance: Sugar has an effect on the survival of Salmonella spp. independent of water activity at 70°C for 48 h. This should be taken into account in the development of predictive models.