Xie Yucen, Long Xiaonuo, Nitin Nitin, Harris Linda J
Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, California 95616-8598, USA.
Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, California 95616-8598, USA; Department of Agricultural and Biological Engineering, University of California, Davis, California 95616, USA.
Int J Food Microbiol. 2025 Feb 2;429:111004. doi: 10.1016/j.ijfoodmicro.2024.111004. Epub 2024 Dec 5.
Contaminated food-contact surfaces are a potential route for spreading microorganisms to stone fruit during postharvest handling. The objective of this study was to investigate the factors that affect the transfer of bacteria from food-contact surfaces to stone fruits. Coupons (1 × 1 cm) of polyurethane (PU) or polyvinyl chloride (PVC) were inoculated with rifampin-resistant variants of Salmonella (five-strain cocktail) or Enterococcus faecium NRRL B-2354 at ~5 or ~7 log CFU/cm. Inoculated coupons (n = 8-11) were attached to a texture analyzer, and uniform contact conditions (5 N, 5 s) were used to explore the impact of bacterial species, inoculation level, donor surface, the presence of dried peach juice or wax, recipient produce commodity, and the dryness of inoculum. Whole fruits were transferred to 20 mL of 0.1 % peptone, rubbed for 2 min, and then the diluent was plated onto tryptic soy agar supplemented with rifampin at 50 μg/mL. Whole fruits were enriched when populations were anticipated to fall below the limit of detection (1.6 log CFU/fruit). At an inoculum of ~5 log CFU/coupon, Salmonella and E. faecium were recovered from the fruit by enrichment but not by plating. At ~7 log CFU/coupon, transfer rates, i.e., ratio of populations on recipient fruit to donor surface, were not significantly (P > 0.05) influenced by either bacterial species (Salmonella [0.26 % ± 0.77 %] versus E. faecium [0.068 % ± 0.071 %]) or donor surface (PU [0.085 % ± 0.098 %] versus PVC [0.16 % ± 0.16 %]). The rates of transfer of E. faecium from contaminated PU to peaches (0.050 % ± 0.031 %), nectarines (0.066 % ± 0.076 %), and onion skins (0.048 % ± 0.059 %) were not significantly different. The mean transfer rates of E. faecium increased significantly (P < 0.05) in the presence of dried wax (18 % ± 16 %) or peach juice (1.3 % ± 2.6 %) on the PU surface compared with the control (0.080 % ± 0.086 %). The transfer rates of E. faecium from contaminated surfaces were also significantly influenced by the drying time post-inoculation; the drier the inoculum, the lower the transfer rates. The presence of residues or moisture on food-contact surfaces facilitated the transfer of microorganisms during dry handling of fresh stone fruits. The results underscore the importance of implementing adequate cleaning, sanitation and, where appropriate, drying of equipment surfaces to effectively remove organic residues and mitigate the risks of cross-contamination.
受污染的食品接触表面是采后处理过程中微生物传播到核果的潜在途径。本研究的目的是调查影响细菌从食品接触表面转移到核果上的因素。将聚氨酯（PU）或聚氯乙烯（PVC）制成的试片（1×1厘米）接种耐利福平的沙门氏菌变异株（五菌株混合菌液）或粪肠球菌NRRL B - 2354，接种量约为5或7 log CFU/平方厘米。将接种后的试片（n = 8 - 11）固定在质地分析仪上，采用均匀的接触条件（5 N，5秒）来探究细菌种类、接种水平、供体表面、干桃汁或蜡的存在、受体农产品种类以及接种物干燥程度的影响。将完整果实转移到20毫升0.1%蛋白胨中，揉搓2分钟，然后将稀释液接种到添加了50μg/毫升利福平的松胨大豆琼脂平板上。当预计菌量降至检测限（1.6 log CFU/果实）以下时，对完整果实进行富集培养。接种量约为5 log CFU/试片时，沙门氏菌和粪肠球菌通过富集培养可从果实中检出，但平板计数法未检出。接种量约为7 log CFU/试片时，转移率（即受体果实上的菌量与供体表面菌量之比）不受细菌种类（沙门氏菌[0.26%±0.77%]对粪肠球菌[0.068%±0.071%]）或供体表面（PU[0.085%±0.098%]对PVC[0.16%±0.16%]）的显著影响（P>0.05）。粪肠球菌从受污染的PU转移到桃子（0.050%±0.031%）、油桃（0.066%±0.076%）和洋葱皮（0.048%±0.059%）上的转移率无显著差异。与对照（0.080%±0.086%）相比，PU表面存在干蜡（18%±16%）或桃汁（1.3%±2.6%）时，粪肠球菌的平均转移率显著增加（P<0.05）。接种后干燥时间也显著影响粪肠球菌从受污染表面的转移率；接种物越干燥，转移率越低。食品接触表面上的残留物或水分在新鲜核果干处理过程中促进了微生物的转移。结果强调了对设备表面进行充分清洁、消毒以及在适当情况下干燥以有效去除有机残留物并降低交叉污染风险的重要性。
