延长贮藏期间散装与包装 d’Anjou 梨上非定植性大肠杆菌的存活情况

亮点
•大肠杆菌在冷藏252天后数量下降，但仍可被检测到。
•分段模型揭示了随时间推移，大肠杆菌在梨上出现的四个 distinct 死亡阶段。
•含铜-乙氧喹的包装纸对细菌减少无不利影响。


Abstract
Due to past outbreaks and recalls linked to tree fruit, more targeted food safety risk mitigation measures are needed in the pear industry. However, there is limited research on food safety risks that are specific to pear packing operations. This study examined the survival of generic Escherichia coli on both unwrapped (bulk) and wrapped in commercial paper (containing 1.3% copper carbonate and 0.1% ethoxyquin) d’Anjou pears under extended periods of controlled atmosphere storage (4℃; 2-3% O2 and 1% CO2). Whole, fresh green d’Anjou pears were inoculated (∼7 log CFU/pear) with a three-strain cocktail of rifampicin-resistant generic E. coli and stored for up to 252 d. Nine pear samples were collected at 13 timepoints, and E. coli concentrations were enumerated. To determine the die-off pattern of E. coli on pears, data was modeled using log-linear, Weibull, and segmented regression approaches. E. coli was still detectable at ∼1.9 log CFU/pear after 252 d regardless of bulk or wrapped storage. Based on Akaike Information Criterion (AIC), a segmented model, with four distinct die-off phases and wrapping as a covariate, best fit E. coli survival on pear surfaces over time. Die-off was best characterized by an initial decline rate of 0.151 log CFU/pear/d from 0 to 8.74 d followed by slower rates of 0.030, 0.014, and 0.010 log CFU/pear/d between 8.74 – 55.97 d, 55.97 – 172.02 d, and 172.02 – 252 d, respectively. These findings provide evidence to inform practical, risk-based control measures for the pear industry.

摘要

由于过去与仁果类水果相关的疫情和召回事件，梨产业需要更有针对性的食品安全风险减缓措施。然而，针对梨包装操作中食品安全风险的研究有限。本研究检测了在延长的气调贮藏期（4℃；2-3% O2 和 1% CO2）内，非定植性大肠杆菌（generic Escherichia coli）在未包装（散装）和商业包装纸（含1.3%碳酸铜和0.1%乙氧喹）包装的 d’Anjou 梨上的存活情况。将新鲜的绿色 d’Anjou 整梨接种（约7 log CFU/梨）含三种耐利福平的非定植性大肠杆菌菌株的混合液，并贮藏长达252天。在13个时间点采集9个梨样品，对大肠杆菌浓度进行计数。为确定梨上大肠杆菌的死亡模式，采用对数线性、Weibull 和分段回归方法对数据进行建模。无论散装还是包装贮藏，252天后大肠杆菌在梨上仍可检测到，约为1.9 log CFU/梨。基于赤池信息准则（AIC），包含四个 distinct 死亡阶段并以包装方式为协变量的分段模型最适合描述梨表面大肠杆菌随时间的存活情况。死亡特征最好描述为：初始阶段（0-8.74天）的下降速率为0.151 log CFU/梨/天，随后在8.74-55.97天、55.97-172.02天和172.02-252天阶段，下降速率分别减慢至0.030、0.014和0.010 log CFU/梨/天。这些发现为梨产业制定基于风险的实用控制措施提供了依据。

Keywords：Bulk,Die-off,GenericE. coli,Nonlinear model,Pears,Wrapped

关键词： 散装，死亡，非定植性大肠杆菌，非线性模型，梨，包装

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Materials and Methods
Pear Storage. 
Pears were assigned to 13 sampling points over a nine month storage period (0, 1, 7, 14, 28, 56, 84, 112, 140, 168, 196, 224, and 252 d). To replicate relevant industry practices, regular atmosphere (RA) cold storage was used to store pears, which were to be enumerated after 0 to 84 d of storage, and controlled atmosphere (CA) cold storage was used to store pears enumerated after 112 to 252 d of storage. RA storage was carried out in a biosafety level I refrigerated storage room operated at 3 – 4°C at the Washington State University Prosser Irrigated Agricultural Research and Extension Center. Pears that were stored in bulk were comingled in a cardboard box. Each wrapped pear was individually wrapped in one 28 cm2 sheet of paper impregnated with copper carbonate (1.3% w/w) and ethoxyquin (0.1% w/w) (Wrap Pack, Yakima, WA). CA storage was carried out in two sealed chambers equipped with circulation fans and automated real-time monitoring of O2 and CO2 sensors (LabPod; Storage Control Systems Inc., MI). These chambers possess an automatic control of built-in gases and were connected to industrial gas tanks (A-L Compressed Gases Inc, Prosser, WA, USA) to adjust concentrations. Each chamber had a capacity of one plastic bin (30 × 40 x 24 cm). One chamber was used for bulk pears, and the second for wrapped pears. CA chambers were maintained at 2-3% O2, 1% CO2, and 3 – 4°C within a biosafety level II laboratory.

梨的贮藏

将梨分配到9个月贮藏期内的13个采样时间点（0、1、7、14、28、56、84、112、140、168、196、224和252天）。为模拟相关行业实践，对贮藏0至84天后计数的梨采用常规大气（RA）冷藏，而对贮藏112至252天后计数的梨采用气调（CA）冷藏。RA贮藏在美国华盛顿州立大学普罗瑟灌溉农业研究与推广中心的一个生物安全一级冷藏室中进行，温度控制在3-4℃。散装贮藏的梨混装在纸板箱中。每个包装梨用一张28 cm²的纸单独包裹，该纸浸渍有碳酸铜（1.3% w/w）和乙氧喹（0.1% w/w）（Wrap Pack, Yakima, WA）。CA贮藏在两个密封的腔室中进行，腔室配有循环风扇和自动实时监测O2及CO2的传感器（LabPod；Storage Control Systems Inc., MI）。这些腔室可自动控制内置气体，并连接到工业气瓶（A-L Compressed Gases Inc, Prosser, WA, USA）以调节气体浓度。每个腔室可容纳一个塑料箱（30 × 40 × 24 cm）。一个腔室用于散装梨，另一个用于包装梨。CA腔室维持2-3% O2、1% CO2和3-4℃的条件，置于生物安全二级实验室内。