Salazar Joelle K, Carstens Christina K, Bathija Vriddi M, Narula Sartaj S, Parish Mickey, Tortorello Mary Lou
U.S. Food and Drug Administration, Division of Food Processing Science and Technology, Bedford Park, Illinois 60501, USA.
Institute for Food Safety and Health, Illinois Institute of Technology, Bedford Park, Illinois 60501, USA.
J Food Prot. 2016 May;79(5):696-702. doi: 10.4315/0362-028X.JFP-15-442.
An outbreak of listeriosis in late 2014 and early 2015 associated with caramel apples led to questions about how this product became a vector for Listeria monocytogenes. This investigation aimed to determine information about the survival and growth of L. monocytogenes in both fresh apples and caramel apples, specifically examining the effects of site and level of inoculation, inoculum drying conditions, and storage temperature. At a high inoculation level (7 log CFU per apple), L. monocytogenes inoculated at the stem end proliferated on Gala caramel apples at both 5 and 25°C and on Granny Smith caramel apples at 25°C by as much as 3 to 5 log CFU per apple. Fresh apples and caramel apples inoculated at the equatorial surface supported survival but not growth of the pathogen. Growth rates (μmax) for apples inoculated at the stem end, as determined using the Baranyi and Roberts growth model, were 1.64 ± 0.27 and 1.38 ± 0.20 log CFU per apple per day for Gala and Granny Smith caramel apples, respectively, stored at 25°C. At a low inoculation level (3 log CFU per apple), L. monocytogenes inoculated at the stem end and the equatorial surface survived but did not grow on fresh Gala and Granny Smith apples stored at 25°C for 49 days; however, on caramel apples inoculated at the stem end, L. monocytogenes had significant growth under the same conditions. Although certain conditions did not support growth, the pathogen was always detectable by enrichment culture. The inoculation procedure had a significant effect on results; when the inoculum was allowed to dry for 24 h at 5°C, growth was significantly slowed compared with inoculum allowed to dry for 2 h at 25°C. Variation in stick materials did affect L. monocytogenes survival, but these differences were diminished once sticks were placed into caramel apples.
2014年末至2015年初发生的一起与焦糖苹果有关的李斯特菌病暴发引发了人们对该产品如何成为单核细胞增生李斯特菌传播媒介的疑问。本研究旨在确定单核细胞增生李斯特菌在新鲜苹果和焦糖苹果中的存活及生长情况，具体考察接种部位和接种量、接种物干燥条件以及储存温度的影响。在高接种量（每个苹果7 log CFU）下，接种于果梗端的单核细胞增生李斯特菌在5℃和25℃的嘎啦焦糖苹果上以及在25℃的澳洲青苹焦糖苹果上增殖，每个苹果最多增加3至5 log CFU。接种于赤道面的新鲜苹果和焦糖苹果能支持该病原体存活，但不能支持其生长。根据Baranyi和Roberts生长模型确定，储存于25℃的嘎啦和澳洲青苹焦糖苹果，接种于果梗端的苹果的生长速率（μmax）分别为每天每个苹果1.64±0.27 log CFU和1.38±0.20 log CFU。在低接种量（每个苹果3 log CFU）下，接种于果梗端和赤道面的单核细胞增生李斯特菌在储存于25℃达49天的新鲜嘎啦和澳洲青苹苹果上存活但未生长；然而，接种于果梗端的焦糖苹果上，单核细胞增生李斯特菌在相同条件下有显著生长。尽管某些条件不支持生长，但通过增菌培养总能检测到该病原体。接种程序对结果有显著影响；当接种物在5℃干燥24小时时，与在25℃干燥2小时的接种物相比，生长显著减缓。棒材材料的差异确实会影响单核细胞增生李斯特菌的存活，但一旦将棒材放入焦糖苹果中，这些差异就会减小。
