Abstract：
During commercial production of liquid egg yolk (LEY), phospholipase A2 (PLA2) is used to improve its emulsification capacity and thermal stability. The enzymatic treatment may occur at elevated temperatures such as 50 °C, potentially allowing foodborne pathogens, such as Bacillus cereus, to grow. Little knowledge is available concerning growth of B. cereus in LEY during PLA2 treatment. Therefore, the objective of this study was to investigate the growth kinetics of B. cereus during PLA2 treatment using pathogenic B. cytotoxicus NVH391-98, the most thermotolerant member in the B. cereus group, as a surrogate. Inoculated LEY samples were placed in precision programmable incubators to observe the growth of B. cytotoxicus NVH391-98 under multiple isothermal and dynamic temperature conditions between 20 and 53 °C. The bacterial growth was described using the differential Baranyi model coupled with two different secondary models. The kinetic parameters were determined using one-step dynamic inverse analysis of multiple growth curves. The least square method was used in combination with the 4th order Runge-Kutta method to solve the differential Baranyi model using multiple growth curves to determine the cardinal kinetic parameters. The results showed that B. cytotoxicus NVH391-98 can grow prolifically at 50 °C. The estimated minimum, optimum and maximum temperatures were 16.7 or 18.5, 47.8 or 48.1, and 52.1 or 52.4 °C, respectively, depending on the secondary models, with an optimum growth rate of 2.1 log colony-forming-unit (CFU)/g per hour. The dynamic model is validated using isothermal curves with reasonable accuracy. B. cytotoxicus died off slowly at 15 °C. At 55 °C, thermal inactivation was observed, with a D value of approximately 2.7 h. Holding at 55 °C or below 15 °C can effectively prevent the growth of B. cytotoxicus in egg yolk.
摘要：
在液体蛋黄（LEY）的商业生产过程中，磷脂酶A2(PLA2)用于提高其乳化能力和热稳定性。酶处理可以在升高的温度如50°C下进行。可能允许食源性病原体，如蜡样芽孢杆菌，成长。关于PLA2治疗期间LEY中蜡样芽孢杆菌生长的知识很少。因此,这项研究的目的是研究使用致病性B.细胞毒素NVH391-98治疗PLA2期间蜡样芽孢杆菌的生长动力学，作为代理人。将接种的LEY样品放置在精密可编程培养箱中，以观察在20至53°C之间的多个等温和动态温度条件下细胞毒素NVH391-98的生长。使用差分Baranyi模型和两个不同的二级模型描述了细菌的生长。使用多个生长曲线的一步动态逆分析确定动力学参数。最小二乘法与4阶Runge-Kutta方法结合使用多个生长曲线求解微分Baranyi模型，以确定基数动力学参数。结果表明，细胞毒素B。NVH391-98可以在50°C下大量生长。估计的最小值，最佳和最高温度分别为16.7或18.5、47.8或48.1和52.1或52.4°C，分别,根据次要模型，最佳生长速率为每小时2.1log菌落形成单位（CFU）/g。使用等温曲线对动力学模型进行了验证，并具有合理的精度。B.细胞毒性在15℃时缓慢死亡。在55°C时,观察到热失活，D值为约2.7h。保持在55°C或低于15°C可以有效防止细胞毒素在蛋黄中的生长。
