Burnham J A, Kendall P A, Sofos J N
Department of Food Science and Human Nutrition, Colorado State University, Fort Collins 80523, USA.
J Food Prot. 2001 Aug;64(8):1244-8. doi: 10.4315/0362-028x-64.8.1244.
Destruction of Escherichia coli O157:H7 was evaluated on inoculated apple slices dehydrated at two temperatures with and without application of predrying treatments. Half-ring slices (0.6 cm thick) of peeled and cored Gala apples were inoculated by immersion for 30 min in a four-strain composite inoculum of E. coli O157:H7. The inoculated slices (8.7 to 9.4 log CFU/g) either received no predrying treatment (control), were soaked for 15 min in a 3.4% ascorbic acid solution, or were steam blanched for 3 min at 88 degrees C immediately prior to drying at 57.2 or 62.8 degrees C for up to 6 h. Samples were plated on tryptic soy (TSA) and sorbitol MacConkey (SMAC) agar media for direct enumeration of surviving bacterial populations. Steam blanching changed initial inoculation levels by +0.3 to -0.7 log CFU/g, while immersion in the ascorbic acid solution reduced the inoculation levels by 1.4 to 1.6 log CFU/g. Dehydration of control samples for 6 h reduced mean bacterial populations by 2.9 log CFU/g (TSA or SMAC) at 57.2 degrees C and by 3.3 (SMAC) and 3.5 (TSA) log CFU/g at 62.8 degrees C. Mean decreases from initial inoculum levels for steam-blanched slices after 6 h of drying were 2.1 (SMAC) and 2.0 (TSA) log CFU/g at 57.2 degrees C, and 3.6 (TSA or SMAC) log CFU/g at 62.8 degrees C. In contrast, initial bacterial populations on ascorbic acid-pretreated apple slices declined by 5.0 (SMAC) and 5.1 (TSA) log CFU/g after 3 h of dehydration at 57.2 degrees C, and by 7.3 (SMAC) and 6.9 (TSA) log CFU/g after 3 h at 62.8 degrees C. Reductions on slices treated with ascorbic acid were in the range of 8.0 to 8.3 log CFU/g after 6 h of drying, irrespective of drying temperature or agar medium used. The results of immersing apple slices in a 3.4% ascorbic acid solution for 15 min prior to drying indicate that a predrying treatment enhances the destruction of E. coli O157:H7 on home-dried apple products.
对接种了大肠杆菌O157:H7的苹果片进行了研究，这些苹果片在两种温度下进行脱水处理，且有无预干燥处理。将去皮去核的嘎啦苹果切成半环状薄片（0.6厘米厚），浸入由四种菌株组成的大肠杆菌O157:H7复合接种物中30分钟进行接种。接种后的薄片（8.7至9.4 log CFU/g）要么不进行预干燥处理（对照），要么在3.4%的抗坏血酸溶液中浸泡15分钟，要么在88摄氏度下蒸汽热烫3分钟，然后立即在57.2或62.8摄氏度下干燥长达6小时。将样品接种在胰蛋白胨大豆（TSA）和山梨醇麦康凯（SMAC）琼脂培养基上，直接计数存活的细菌数量。蒸汽热烫使初始接种水平变化了+0.3至 -0.7 log CFU/g，而浸入抗坏血酸溶液使接种水平降低了1.4至1.6 log CFU/g。对照样品在57.2摄氏度下脱水6小时后，平均细菌数量减少了2.9 log CFU/g（TSA或SMAC），在62.8摄氏度下减少了3.3（SMAC）和3.5（TSA）log CFU/g。干燥6小时后，蒸汽热烫薄片的初始接种水平平均下降量在57.2摄氏度下为2.1（SMAC）和2.0（TSA）log CFU/g，在62.8摄氏度下为3.6（TSA或SMAC）log CFU/g。相比之下，抗坏血酸预处理的苹果片在57.2摄氏度下脱水3小时后，初始细菌数量下降了5.0（SMAC）和5.1（TSA）log CFU/g，在62.8摄氏度下脱水3小时后下降了7.3（SMAC）和6.9（TSA）log CFU/g。无论干燥温度或使用的琼脂培养基如何，抗坏血酸处理的薄片在干燥6小时后的减少量在8.0至8.3 log CFU/g范围内。在干燥前将苹果片浸入3.4%的抗坏血酸溶液中15分钟的结果表明，预干燥处理可增强家庭干燥苹果制品中大肠杆菌O157:H7的破坏。
