Effect of Nisin and Storage Temperature on Outgrowth of Bacillus cereus Spores in Pasteurized Liquid Whole Eggs

Pasteurization is used to ensure the safety of liquid whole eggs (LWEs) before commercial distribution; however, it is insufficient to inactivate the spore-forming bacteria <i>Bacillus cereus</i>. This study investigated the effect of nisin on the growth kinetics of <i>B. cereus</i> in LWE. Samples supplemented with 0-6.25 ppm of nisin were inoculated with a four-strain cocktail of heat-shocked <i>B. cereus</i> spores and incubated at isothermal temperatures of 15-45 °C. The Baranyi model was fitted to all <i>B. cereus</i> isothermal growth profiles, generating maximum growth rate (µ_max) and lag phase duration (LPD). The extended Ratkowsky square root model described the temperature dependency of µ_max. A second-order polynomial model assessed the combined effects of temperature and nisin on the LPD of <i>B. cereus</i> in LWE. A tertiary model was developed and validated using three dynamic temperature profiles. Nisin significantly extended LPD at lower temperatures, while µ_max remained unaffected. Samples with 6.25 ppm of nisin inhibited growth for 29 days (average) at 15 °C. Although the tertiary model accurately predicted growth rates, it underpredicted LPD. Adjusting h₀ values for each experimental condition improved LPD prediction accuracy. The study's findings indicate that nisin is effective in inhibiting the growth of <i>B. cereus</i> spores in LWE, lowering the risk of illness.