Midwest Dairy Foods Research Center, Dairy and Food Science Department, South Dakota State University, Brookings 57007.
Midwest Dairy Foods Research Center, Dairy and Food Science Department, South Dakota State University, Brookings 57007.
J Dairy Sci. 2021 Mar;104(3):2787-2793. doi: 10.3168/jds.2019-18071. Epub 2021 Jan 21.
Ice cream handling and serving conditions on the consumer side may result in temperature abuse before consumption. Under some extreme conditions, even the sporadic presence of injured bacterial cells might pose a health risk due to the possibility of recovery of those cells. We conducted this investigation to evaluate the potential of injured cells of Listeria innocua to recover under ice cream temperature abuse conditions and on exposure to simulated gastrointestinal (GI) fluids. Ice cream mix samples (42% total solids), spiked with 4 log cfu/g of Listeria innocua, were thermally treated at 69°C for 30 min. Potential heat-injured cells were recovered in buffered Listeria broth (BLEB), followed by isolation on Listeria-specific modified Oxford agar (MOX). The ice cream mix samples, containing potentially injured cells of Listeria innocua, were followed through overnight aging (7°C), freezing (-3.3°C), and overnight hardening (-40°C) steps to obtain the final ice cream samples. To simulate temperature abuse conditions, the samples were held for 12 h at 4.4°C, followed by 30 min at room temperature (22°C); this treatment was considered the first cycle of temperature abuse. To generate a worst-case scenario, the samples were exposed to 3 such consecutive temperature abuse cycles. At the end of each cycle, direct plating was done on MOX to recover viable cells, and BLEB enrichment verified the presence of potential injured cells. In addition, the ice cream samples, containing potential injured cells, were passed through simulated GI fluids. As a first step, samples were mixed (1:1) with simulated gastric fluids (pH 1.0 and 2.0 before mixing) and held at 37°C in a shaker incubator. Samples drawn at 15, 30, and 60 min were analyzed for viable and potential injured cells. To study the effect of sequential transit through simulated intestinal fluid, a mixture of ice cream and gastric fluid (1:1) from the gastric fluid experiment above was added to simulated intestinal fluid (pH 6.8) and held at 37°C. Samples were analyzed at 30 and 360 min for viable and potential injured cells. Three trials were conducted and the samples collected in duplicates. The temperature abuse or GI fluid exposure studies did not result in the recovery of potential injured cells of Listeria innocua in the ice cream samples under the conditions tested. Exposure to gastric fluids, however, did not eliminate the potential injured cells. Further studies are necessary to understand the exact risk implications of these findings.
冰淇淋在消费者端的处理和食用条件可能导致食用前的温度滥用。在某些极端条件下，即使偶尔存在受伤的细菌细胞，也可能由于这些细胞的恢复可能性而构成健康风险。我们进行了这项调查，以评估在冰淇淋温度滥用条件下和暴露于模拟胃肠道（GI）流体时，无害李斯特菌受伤细胞的恢复潜力。将含有 4 对数 cfu/g 无害李斯特菌的冰淇淋混合物样品（总固体含量为 42%）在 69°C 下热处理 30 分钟。潜在的热损伤细胞在缓冲李斯特菌肉汤（BLEB）中回收，然后在李斯特菌特异性改良牛津琼脂（MOX）上分离。含有潜在受伤的无害李斯特菌细胞的冰淇淋混合物样品经过过夜老化（7°C）、冷冻（-3.3°C）和过夜硬化（-40°C）步骤，以获得最终的冰淇淋样品。为了模拟温度滥用条件，将样品在 4.4°C 下保持 12 小时，然后在室温（22°C）下放置 30 分钟；这被认为是第一个温度滥用周期。为了生成最坏情况场景，样品经历了 3 个连续的温度滥用周期。在每个周期结束时，直接在 MOX 上进行平板计数以回收活菌，并通过 BLEB 富集验证潜在受伤细胞的存在。此外，含有潜在受伤细胞的冰淇淋样品通过模拟胃肠道流体。作为第一步，将样品（1:1）与模拟胃液（混合前 pH 值为 1.0 和 2.0）混合，并在摇床培养箱中在 37°C 下保持。在 15、30 和 60 分钟时抽取样品，分析活菌和潜在受伤细胞。为了研究通过模拟肠液的连续转移的影响，将上述胃液实验中的冰淇淋和胃液混合物（1:1）加入模拟肠液（pH 值 6.8）中，并在 37°C 下保持。在 30 和 360 分钟时分析样品的活菌和潜在受伤细胞。进行了三次试验，收集了双份样品。在测试条件下，冰淇淋样品中未发现无害李斯特菌潜在受伤细胞的恢复。然而，暴露于胃液并没有消除潜在受伤的细胞。需要进一步的研究来了解这些发现的确切风险含义。
