苹果果实性状和采后条件对单核细胞增生李斯特菌存活的影响

The Effect of Apple (Malus domestica) Fruit Attributes and Post-Harvest Conditions on Listeria monocytogenes Survival

2024-苹果果实性状和采后条件对单核细胞增生李斯特菌存活的影响

Natasha Rae Sloniker

ABSTRACT
Multiple recalls and outbreaks involving Listeria monocytogenes-contaminated apples have been linked to the post-harvest packing environment where this pathogen persists. The research presented here addresses the effect of both apple fruit attributes and post-harvest conditions on L. monocytogenes survival. First, L. monocytogenes survival was assessed on apples as affected by harvest year, apple cultivar, storage atmosphere, and growth conditions. The second portion of the study investigated the chemical composition and morphology differences of cuticular wax in Gala and Honeycrisp apples. The influence of natural cuticular wax composition and structure is important to investigate as it impacts apple fruit quality and food safety. Finally, before apple fruit are shipped to market, they are treated with commercial coatings to enhance quality. We assessed L. monocytogenes survival to determine the impact shellac and carnauba surface coatings have during storage in solution or applied to a contaminated surface. On the surface of apples, L. monocytogenes populations gradually decreased but were still quantifiable in most samples after 7 months. Apple cultivar significantly impacted L. monocytogenes survival (p < 0.05) during both harvest years with greater reductions (p < 0.05) seen on Gala compared to Granny Smith and Honeycrisp. Gala apples had more alkanes (g/cm2 of peel) overall for alkane compounds compared to Honeycrisp. In Gala apples the main component of the cuticular wax was nonacosane. Nonacosane content (g/cm2 of peel) in the cuticular waxes was greater (p < 0.01) on Gala (108.77±0.36) than on Honeycrisp (46.12±4.86). After just 12 hours of storage, in the shellac surface coating solution, L. monocytogenes was no longer detectable, compared to the carnauba surface coating solution which still supported survival (2.4-4.0 log CFU/mL) after 14 days. These findings should aid in the development of improved L. monocytogenes intervention strategies and inform manufacturers looking for natural food safety solutions.

涉及单核细胞增生李斯特菌污染的苹果的多次召回和爆发与这种病原体持续存在的采后包装环境有关。本研究探讨了苹果果实属性和采后条件对单核细胞增生李斯特菌存活的影响。首先，对苹果单核细胞增生李斯特菌的存活率进行了评估，认为其受收获年份、苹果品种、储存环境和生长条件的影响。研究的第二部分调查了Gala和Honeycrisp苹果表皮蜡的化学成分和形态差异。天然表皮蜡的组成和结构对苹果果实质量和食品安全的影响值得研究。最后，在苹果水果运往市场之前，它们会用商业涂料进行处理以提高质量。我们评估了单核细胞增生李斯特菌的存活率，以确定虫胶和巴西棕榈表面涂层在溶液中储存或应用于受污染表面时的影响。在苹果表面，单核细胞增生李斯特菌的数量逐渐减少，但在7个月后，大多数样本中的数量仍然可以量化。苹果品种在两个收获年份都显著影响了单核细胞增生李斯特菌的存活率（p<0.05），与Granny Smith和Honeycrip相比，Gala的存活率降低幅度更大（p<0.05）。与Honeycrip相比，Gala苹果的烷烃化合物总体上更多（g/cm2果皮）。在Gala苹果中，表皮蜡的主要成分是九烷。Gala（108.77±0.36）的表皮蜡中非甾体含量（g/cm2果皮）高于Honeycrip（46.12±4.86）（p<0.01）。在虫胶表面涂层溶液中储存仅12小时后，与巴西棕榈表面涂层溶液相比，单核细胞增生李斯特菌不再可检测到，巴西棕榈表面涂料溶液在14天后仍能维持存活（2.4-4.0 log CFU/mL）。这些发现应有助于制定改进的单核细胞增生李斯特菌干预策略，并为寻求天然食品安全解决方案的制造商提供信息。

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3.3 Materials and Methods
Apples and Storage Conditions. Unwaxed Gala, Granny Smith, and Honeycrisp apples (6–8 cm dia.) were shipped from three major apple-growing regions in the United States (Midwest, Northeast, and Northwest) to Michigan State University during the 2019 and 2020 harvest seasons. Upon arrival, any damaged or under-sized apples were discarded. The remaining apples were stored in 0.93 m3 aluminum chambers (Storage Control Systems, Sparta, MI) under air or controlled atmosphere (CA) (1.5% O2, 1.5% CO2) in a 2 °C cold room and treated within 7 d of arrival with 1 μL/L 1-methylcyclopropene for 24 h to suppress ripening and preserve fruit quality. The chamber atmosphere was regulated by an automated atmosphere control system (ICA 61 Laboratory System: International Controlled Atmosphere Ltd., Paddock Wood, UK), with the temperature monitored continuously.

苹果和储存条件。在2019年和2020年的收获季节，未打蜡的Gala、Granny Smith和Honeycrisp苹果（直径6-8厘米）从美国三个主要的苹果种植区（中西部、东北部和西北部）运往密歇根州立大学。抵达后，任何损坏或尺寸过小的苹果都会被丢弃。剩余的苹果在2°C的冷藏室中，在空气或气调（CA）（1.5%O2，1.5%CO2）下贮藏在0.93 m³的铝室（Storage Control Systems，Sparta，MI）中，并在到达后7天内用1μL/L的1-甲基环丙烯处理24小时，以抑制成熟并保持果实质量。室气体由自动气调控制系统（ICA 61 Laboratory system：International Controlled atmosphere ltd，Paddock Wood，UK）调节，并持续监测温度。