Derrickson-Tharrington Elizabeth, Kendall Patricia A, Sofos John N
Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, CO 80523, United States.
Int J Food Microbiol. 2005 Mar 1;99(1):79-89. doi: 10.1016/j.ijfoodmicro.2004.07.015.
Inactivation of Escherichia coli O157:H7 was evaluated on inoculated apple slices without pretreatment or pretreated by immersing in water or acid solutions commonly used to help retain apple color during dehydration, then stored at ambient temperature or dried for 6 h. Half-ring slices (0.6 cm thick) of peeled and cored Gala apples were inoculated by immersion for 30 min in a three-strain composite inoculum of E. coli O157:H7 (7.8-8.0 CFU/g). Inoculated slices received (1) no pre-drying treatment (control); or a 10-min immersion in solutions of (2) sterile water, (3) 2.8% ascorbic acid, (4) 1.7% citric acid, (5) 50% commercial lemon juice, or (6) 50% commercial lemon juice with preservatives. Drained slices were placed in sterile plastic bags and stored at room temperature (25+/-2 degrees C) for up to 6 h or dehydrated (62.8 degrees C) for up to 6 h. Samples were plated on tryptic soy agar (TSA) and sorbitol MacConkey agar (SMAC) for direct enumeration of surviving bacteria at various time intervals. Immersion in sterile water or acidic solutions caused initial bacterial reductions of 0.9-1.3 log CFU/g on apple slices. Between 0 and 6 h of storage at room temperature, slices dipped in acidic solutions showed minor changes in bacterial populations (-0.2 to +0.6 log CFU/g) compared to a 1.1 log CFU/g increase for slices dipped in sterile water. The no treatment samples (control) showed an increase in bacterial populations of 1.3-1.5 CFU/g over the 6-h holding time. For apple slices dried at 62.8 degrees C, bacterial populations were reduced by 2.5 (SMAC) and 3.1 (TSA) log CFU/g in the control (no pre-drying treatment) samples following 6 h dehydration. The slices immersed in sterile water showed a 5.8 (SMAC) and 5.1 (TSA) reduction after 6 h of dehydration. In contrast, after 6 h of dehydration bacterial populations on the four acid-pretreated products were reduced by 6.7-7.3 log CFU/g. The results showed that acidic treatment alone was not effective in destroying E. coli O157:H7 on apple slices but did inhibit growth of the organism during holding before drying. However, pretreatment of the apple slices with common household acidulants enhanced destruction of E. coli O157:H7 during drying compared to slices dried without treatment.
对接种了大肠杆菌O157:H7的苹果切片进行灭活评估，这些切片未经预处理，或通过浸泡在常用于脱水过程中帮助保持苹果色泽的水或酸性溶液中进行预处理，然后在室温下储存或干燥6小时。将去皮去核的嘎啦苹果切成半环状薄片（0.6厘米厚），通过浸泡在大肠杆菌O157:H7的三菌株复合接种物（7.8 - 8.0 CFU/g）中30分钟进行接种。接种后的切片接受以下处理：(1) 不进行预干燥处理（对照）；或在以下溶液中浸泡10分钟：(2) 无菌水，(3) 2.8%抗坏血酸，(4) 1.7%柠檬酸，(5) 50%市售柠檬汁，或(6) 含防腐剂的50%市售柠檬汁。沥干后的切片放入无菌塑料袋中，在室温（25±2℃）下储存长达6小时或在62.8℃下干燥长达6小时。在不同时间间隔对样品进行平板接种到胰蛋白胨大豆琼脂（TSA）和山梨醇麦康凯琼脂（SMAC）上，以直接计数存活细菌。浸泡在无菌水或酸性溶液中会使苹果切片上的细菌初始减少0.9 - 1.3 log CFU/g。在室温下储存0至6小时期间，浸泡在酸性溶液中的切片细菌数量变化较小（-0.2至+0.6 log CFU/g），而浸泡在无菌水中的切片细菌数量增加了1.1 log CFU/g。未处理的样品（对照）在6小时的保存时间内细菌数量增加了1.3 - 1.5 log CFU/g。对于在62.8℃干燥的苹果切片，对照（未进行预干燥处理）样品在脱水6小时后，细菌数量在SMAC上减少了2.5 log CFU/g，在TSA上减少了3.1 log CFU/g。浸泡在无菌水中的切片在脱水6小时后减少了5.8（SMAC）和5.1（TSA）log CFU/g。相比之下，四种经酸预处理的产品在脱水6小时后细菌数量减少了6.7 - 7.3 log CFU/g。结果表明，单独的酸性处理对破坏苹果切片上的大肠杆菌O157:H7无效，但在干燥前的保存期间确实抑制了该菌的生长。然而，与未经处理干燥的切片相比，用常见家用酸化剂对苹果切片进行预处理可增强干燥过程中大肠杆菌O157:H7的破坏。
