Department of Animal and Food Sciences, University of Delaware, Newark, DE, 19716-2150, USA.
Department of Animal and Food Sciences, University of Delaware, Newark, DE, 19716-2150, USA.
Food Microbiol. 2023 Aug;113:104269. doi: 10.1016/j.fm.2023.104269. Epub 2023 Mar 22.
This study investigated the effects of inoculation method, water activity (a), packaging method, and storage temperature and duration on the survival of Salmonella on almonds as well as their resistance to subsequent thermal treatments. Whole almond kernels were inoculated with a broth-based or agar-based growth Salmonella cocktail and conditioned to a of 0.52, 0.43 or 0.27. Inoculated almonds with a of 0.43 were treated with a previously validated treatment (4 h of dry heat at 73 °C) to determine the potential differences in heat resistance resulted from the two inoculation methods. The inoculation method did not significantly (P > 0.05) impact the thermal resistance of Salmonella. Inoculated almonds at a of 0.52 and 0.27 were either vacuum packaged in moisture-impermeable mylar bags or non-vacuum packaged in moisture-permeable polyethylene bags before stored at 35, 22, 4, or -18 °C for up to 28 days. At selected storage intervals, almonds were measured for a, analyzed for Salmonella population level, and subjected to dry heat treatment at 75 °C. Over the month-long storage of almonds, Salmonella populations remained almost unchanged (<0.2 log CFU/g) at 4 °C and -18 °C and declined slightly (<0.8 log CFU/g) at 22 °C and more substantially (1.6-2.0 log CFU/g) at 35 °C regardless of the inoculation method, packaging method, and almond a. When stored at 35 °C, almonds with initial a of 0.52 had significantly higher (P < 0.05) Salmonella reductions than those with initial a of 0.27. Prior storage of almonds vacuum packaged in mylar bags at temperatures between -18 °C and 35 °C for 28 days affected their a levels but did not significantly (P > 0.05) affect the subsequent thermal resistance of Salmonella at 75 °C regardless of almond a and storage duration. Salmonella on almonds with higher a was more sensitive to heat treatment than those with lower a. To achieve >5 log CFU/g reductions of Salmonella, a dry heat treatment at 75 °C for 4 and 6 h was needed for almonds with initial a of 0.52 and 0.27, respectively. When applying the dry heating technology for almond decontamination, the processing time needs to be determined based on initial a of almonds regardless of storage condition or age of almonds within the current design frame.
本研究调查了接种方法、水活度（a）、包装方法以及贮藏温度和时间对杏仁上沙门氏菌存活和后续耐热性的影响。整颗杏仁核用基于肉汤或琼脂的生长沙门氏菌混合物接种，并调节至 a 值为 0.52、0.43 或 0.27。用已验证的处理方法（73°C 下干燥热 4 小时）处理接种 a 值为 0.43 的杏仁，以确定两种接种方法导致的耐热性差异。接种方法对沙门氏菌的耐热性没有显著影响（P>0.05）。a 值为 0.52 和 0.27 的接种杏仁要么在真空包装在不透水的聚酯袋中，要么在非真空包装在透湿聚乙烯袋中，然后在 35、22、4 或-18°C 下储存长达 28 天。在选定的储存间隔内，测量杏仁的 a 值、分析沙门氏菌种群水平，并在 75°C 下进行干热处理。在长达一个月的杏仁储存过程中，无论接种方法、包装方法和杏仁 a 值如何，沙门氏菌种群数量在 4°C 和-18°C 下几乎不变（<0.2 log CFU/g），在 22°C 和 35°C 下略有下降（<0.8 log CFU/g），更显著（1.6-2.0 log CFU/g）。当在 35°C 下储存时，初始 a 值为 0.52 的杏仁中沙门氏菌的减少量明显高于初始 a 值为 0.27 的杏仁（P<0.05）。将真空包装在聚酯袋中的杏仁在-18°C 和 35°C 之间储存 28 天，会影响其 a 值，但无论杏仁 a 值和储存时间如何，对随后在 75°C 下的沙门氏菌耐热性均无显著影响（P>0.05）。a 值较高的杏仁上的沙门氏菌对热处理更敏感，而 a 值较低的则不太敏感。为了实现沙门氏菌减少>5 log CFU/g，需要对初始 a 值分别为 0.52 和 0.27 的杏仁进行 75°C 干燥热处理 4 小时和 6 小时。在应用杏仁消毒的干燥加热技术时，无论储存条件如何，也无论杏仁在当前设计框架内的年龄如何，都需要根据初始 a 值确定加工时间。
