Exploring the Nexus Between Emulsifier Characteristics and Salmonella Typhimurium Viability in Oil-in-Water Emulsions

Abstract

Molecular characteristics of emulsifiers such as their molecular weight (MW) and surface charge, not only affect the stability of the emulsion but also can have an impact on its capacity to either inhibit or promote microbial proliferation. These characteristics can affect the behavior of pathogens such as Salmonella Typhimurium in emulsion systems. The growth and thermal resistance of S. Typhimurium were monitored at different oil content levels (20%, 40%, and 60%) in emulsions stabilized by three whey protein-based emulsifiers: whey protein isolate (WPI), whey protein hydrolysate (WPH), and a modified WPI with an alteration of charge (WPI⁺). Our study revealed that emulsifier itself with different MW and surface charge had no effect on bacterial growth and inactivation without oil inclusion (p > 0.05). However, it was found that higher bacterial growth rate at 60% oil content emulsion stabilized with WPI⁺ (0.65 ± 0.03 log CFU/h) than WPI (0.19 ± 0.04 log CFU/h), which showed the charge of emulsifiers has different effects on microbial dynamics in oil-in-water emulsion. Interestingly, WPI⁺ in emulsions also seemed to convey protection against thermal inactivation of bacteria. These data describe a complex interrelationship between the physicochemical characteristics of the emulsifier and its interacting nature with bacterial cells. They throw even more light on the insight about the importance of a strategic approach toward emulsifier selection in food formulations. This is crucial for the food safety and stability of products.

Keywords: Salmonella Typhimurium; emulsifier; emulsion; molecular weight; surface charge.

FIGURE 1

Growth dynamics of S. Typhimurium at 37°C across different mediums: (a) TSB and WPI solutions, alongside emulsions with 20%, 40%, and 60% oil content; (b) TSB and WPH solutions, alongside emulsions with 20%, 40%, and 60% oil content; (c) TSB adjusted to pH 5.0, WPI⁺ solutions, and emulsions containing 20%, 40%, and 60% oil content. The logistic growth model was applied to fit the experimental data, with the solid lines representing the average model fit for the observed growth patterns. Each data point reflects the mean of three replicates, presented with the corresponding standard deviation (SD).

FIGURE 2

Thermal inactivation of S. Typhimurium at 55°C within various mediums: TSB, TSB adjusted to pH 5.0, and emulsions containing WPI, WPH, or WPI⁺ as emulsifiers, each with a 60% oil phase. The Weibull model was employed to fit the experimental observations, with solid lines illustrating the average fit across the inactivation curves. The values presented for each point represent the mean from three independent experiments, accompanied by the standard deviation (SD) to indicate variability.