Abstract：
Microbial challenge studies using nonpathogenic surrogates provide a practical means for validating thermally based pathogen controls for low-moisture foods. Because the relative thermal resistance, or kill ratio, of Enterococcus faecium NRRL B-2354 (a nonpathogenic surrogate) to Salmonella is greatly influenced by food composition, this study assessed relative thermal resistance of a five-strain Salmonella cocktail and E. faecium in skim milk powder (SMP), lactose-free skim milk powder (LSMP), 90% milk protein isolate (MPI), and lactose powder (LP). The impact of sugar composition (lactose versus glucose-galactose) on resuscitation of bacterial survivors, by using SMP and LSMP, was also determined. Dairy powders were inoculated with agar-grown cultures, mixed, preequilibrated at 0.25 water activity (aw), ground to achieve homogeneity, reequilibrated, and subjected to isothermal treatment. After enumeration on nonselective differential media, log-linear and Bigelow models were fit to the survivor data via one-step global regression. The aw changes and glass transition temperature were assessed at elevated temperatures by using uninoculated, equilibrated powder samples. Estimated D90°C-values were approximately two times higher for E. faecium (P < 0.05) than for Salmonella in SMP, LP, and MPI, but statistically similar (P > 0.05) in LSMP. Addition of sugars to recovery media did not influence survivor resuscitation from heat-treated SMP and LSMP, confirming that microbial inactivation was impacted primarily by the thermal treatment, not the recovery step. Thermally induced changes in aw were seen only for LP and MPI, with the glass transition temperature observed only for SMP and MPI. In conclusion, rather than always requiring greater lethality of E. faecium than Salmonella, these findings suggest that sufficient pathogen controls for low-moisture foods can also be validated by thoroughly documenting the appropriate kill ratios of E. faecium to Salmonella.
摘要：
使用非致病性替代品的微生物挑战研究为验证低水分食品的基于热的病原体控制提供了一种实用的方法。因为相对热阻，或杀死率，沙门氏菌的屎肠球菌NRRLB-2354（非致病性替代品）受食物成分的影响很大，这项研究评估了脱脂奶粉（SMP）中的五菌株沙门氏菌鸡尾酒和屎肠球菌的相对耐热性，无乳糖脱脂奶粉（LSMP），90%乳分离蛋白(MPI),和乳糖粉（LP）。糖成分（乳糖与葡萄糖-半乳糖）对细菌幸存者复苏的影响，通过使用SMP和LSMP，也决心。用琼脂培养的培养物接种乳粉，混合,在0.25水活度(aw)下预平衡，地面实现均匀性，重新平衡，并进行等温处理。在非选择性差分介质上进行枚举后，对数线性和Bigelow模型通过一步全局回归拟合幸存者数据。通过使用未接种的，在升高的温度下评估aw变化和玻璃化转变温度，平衡的粉末样品。在SMP中，屎肠球菌的估计D90°C值大约是沙门氏菌的两倍（P<0.05），LP,MPI,但LSMP在统计学上相似(P>0.05)。向恢复培养基中添加糖不会影响经过热处理的SMP和LSMP的幸存者复苏，确认微生物灭活主要受热处理的影响，不是恢复步骤。仅在LP和MPI中观察到热诱导的aw变化，仅对SMP和MPI观察到玻璃化转变温度。总之,而不是总是需要比沙门氏菌更高的屎肠球菌杀伤力，这些研究结果表明,对低水分食品的足够的病原体控制也可以通过彻底记录屎肠球菌与沙门氏菌的适当杀伤比率来验证.
