Influence of Monostearin on the Survival of Salmonella in a Low-water Activity Peanut Protein Model Food System at 37°C and 70°C

Introduction: Several multi-state outbreaks of Salmonella in low-water activity (a_w) foods have raised concern of its survival in peanut-based products.  Salmonella has demonstrated the ability to survive in low a_w foods for long periods of time.  Peanut butters may be formulated with emulsifiers containing monoglycerides, some of which are reported to have antimicrobial effects.

Purpose: The purpose of this study was to investigate the role of monostearin on the survival of Salmonella in a peanut flour model food system at a_w of 0.46 at 70°C and 37°C.

Methods: Monostearin was homogenized with 50% (w/w) defatted peanut flour and 55% (w/w) peanut oil to obtain 0% and 1.625% (w/w) emulsifier concentrations and was equilibrated to a_w = 0.46 (± 0.04).  A dried cocktail of Salmonella Agona, Salmonella Montevideo, Salmonella Tennessee, and Salmonella Typhimurium was added and the samples were treated at 70°C for 48 h and 37°C for 28 d.  Surviving Salmonella were recovered at various times using supplemented tryptic soy agar and log CFU values were compared at each time point using two-way ANOVA. 

Results: At 70°C, survival of Salmonella was not affected by monostearin (P = 0.28, α = 0.05).  The average log reduction was 3.02 with monostearin and 3.59 without monostearin after 48 h.  At 37°C, survival was not affected by monostearin (P = 0.80, α = 0.05).  The average log reduction was 1.94 with monostearin and 1.78 without monostearin after 28 d. 

Significance: This data indicates that monostearin does not affect the survival of Salmonella in peanut-based products at a_w = 0.46 at 70°C for 48 h and at 37°C for 28 d.  These findings will be useful for predictive modeling of Salmonella survival in a low-water activity (a_w = 0.46) model food system.