Dingman D W
Connecticut Agricultural Experiment Station, New Haven, Connecticut 06504, USA.
Appl Environ Microbiol. 2000 Mar;66(3):1077-83. doi: 10.1128/AEM.66.3.1077-1083.2000.
Four of five apple cultivars (Golden Delicious, Red Delicious, McIntosh, Macoun, and Melrose) inoculated with Escherichia coli O157:H7 promoted growth of the bacterium in bruised tissue independent of the date of harvest (i.e., degree of apple ripening) or the source of the apple (i.e., tree-picked or dropped fruit). Apple harvest for this study began 4 September 1998 and ended 9 October, with weekly sampling. Throughout this study, freshly picked (<2 days after harvest) McIntosh apples usually prevented the growth of E. coli O157:H7 for 2 days. Growth of E. coli O157:H7 did occur following 6 days of incubation in bruised McIntosh apple tissue. However, the maximum total cell number was approximately 80-fold less than the maximum total cell number recovered from Red Delicious apples. When fruit was stored for 1 month at 4 degrees C prior to inoculation with E. coli O157:H7, all five cultivars supported growth of the bacterium. For each apple cultivar, the pH of bruised tissue was significantly higher and degrees Brix was significantly lower than the pH and degrees Brix of undamaged tissue regardless of the source. In freshly picked apples, changes in the pH did not occur over the harvest season. Bruised Golden Delicious, McIntosh, and Melrose apple tissue pHs were not significantly different (tree-picked or dropped), and the degrees Brix values of McIntosh, Macoun, and Melrose apple tissue were not significantly different. Single-cultivar preparations of cider did not support growth of E. coli, and the cell concentration of inoculated cider declined over an 11-day test period. The rate of decline in E. coli cell concentration in the McIntosh cider was greater than those in the other ciders tested. The findings of this study suggested that the presence of some factor besides, or in addition to, pH inhibited E. coli growth in McIntosh apples.
用大肠杆菌O157:H7接种的五个苹果品种（金冠、红富士、乔纳金、麦金托什和梅尔罗斯）中有四个品种，无论收获日期（即苹果成熟度）或苹果来源（即树上采摘或掉落的果实）如何，该细菌在碰伤组织中均能促进生长。本研究的苹果收获从1998年9月4日开始，10月9日结束，每周进行采样。在整个研究过程中，刚采摘的（收获后不到2天）麦金托什苹果通常能在2天内抑制大肠杆菌O157:H7的生长。在碰伤的麦金托什苹果组织中培养6天后，大肠杆菌O157:H7确实生长了。然而，最大总细胞数比从红富士苹果中回收的最大总细胞数少约80倍。当果实在接种大肠杆菌O157:H7之前于4℃下储存1个月时，所有五个品种都支持该细菌的生长。对于每个苹果品种，无论来源如何，碰伤组织的pH值显著更高，而糖度显著低于未受损组织的pH值和糖度。在刚采摘的苹果中，pH值在收获季节没有变化。碰伤的金冠、麦金托什和梅尔罗斯苹果组织的pH值没有显著差异（树上采摘或掉落的），麦金托什、麦库恩和梅尔罗斯苹果组织的糖度值也没有显著差异。单一品种的苹果酒制剂不支持大肠杆菌的生长，并且在11天的测试期内接种苹果酒的细胞浓度下降。麦金托什苹果酒中大肠杆菌细胞浓度的下降速率大于其他测试苹果酒中的下降速率。本研究结果表明，除pH值之外或之外还有其他因素抑制了麦金托什苹果中大肠杆菌的生长。
