Wiegand K M, Ingham S C, Ingham B H
Department of Food Science, University of Wisconsin-Madison, 1605 Linden Drive, Madison, Wisconsin 53706, USA.
J Food Prot. 2009 Aug;72(8):1727-31. doi: 10.4315/0362-028x-72.8.1727.
Heat shock of Escherichia coli O157:H7 in broth media reportedly leads to enhanced survival during subsequent heating in broth medium or ground beef. Survival of E. coli O157:H7 during slow cooking thus may be enhanced by prior exposure to sublethal heat shock conditions, thereby jeopardizing the safety of slow-cooked products such as beef roasts. This study examined the effect of heat shocking E. coli O157:H7-inoculated lean (6 to 9% fat) ground beef on the survival of the pathogen in the same ground beef during a subsequent 4-h, 54.4 degrees C cooking process. Six different combinations of heat shock temperature (47.2, 48.3, or 49.4 degrees C) and time (5 or 30 min) were applied to a five-strain cocktail of microaerophilically grown cells in 25 g of prewarmed ground beef, which was followed by cooking at 54.4 degrees C. Temperature during a 30-min heat shock treatment did not significantly affect E. coli O157:H7 survival during subsequent isothermal cooking (P > 0.05). Survival after a 5-min heat shock was higher when the heat shock temperature was 48.3 or 49.4 degrees C (P < 0.05) than when it was 47.2 degrees C. The D-values at 54.4 degrees C (130 degrees F) (D54.4-value) of the process significantly increased only when cells were exposed to a heat shock combination of 5 min at 49.4 degrees C. Mean (n = 3 trials) reductions in E. coli O157:H7 during the 4-h, 54.4 degrees C isothermal cooking process ranged from 4.3 to 7.5 log CFU/g. Heating E. coli O157:H7-contaminated beef at the high end of the sublethal temperature range for 5 min could increase survival of E. coli O157:H7 during subsequent slow-cooking processes.
据报道，肉汤培养基中大肠杆菌O157:H7的热休克会导致其在随后的肉汤培养基或碎牛肉加热过程中存活率提高。因此，大肠杆菌O157:H7在慢煮过程中的存活可能会因事先暴露于亚致死热休克条件而提高，从而危及烤牛肉等慢煮产品的安全性。本研究考察了对接种大肠杆菌O157:H7的低脂（6%至9%脂肪）碎牛肉进行热休克处理，对同一碎牛肉中该病原体在随后4小时、54.4℃烹饪过程中存活情况的影响。将六种不同的热休克温度（47.2、48.3或49.4℃）和时间（5或30分钟）组合应用于25克预热碎牛肉中微需氧培养的五株混合菌，然后在54.4℃下烹饪。30分钟热休克处理期间的温度对随后等温烹饪过程中大肠杆菌O157:H7的存活没有显著影响（P>0.05）。当热休克温度为48.3或49.4℃时，5分钟热休克后的存活率高于47.2℃时（P<0.05）。仅当细胞暴露于49.4℃ 5分钟的热休克组合时，该过程在54.4℃（130℉）的D值（D54.4值）才显著增加。在4小时、54.4℃等温烹饪过程中，大肠杆菌O157:H7的平均（n = 3次试验）减少量为4.3至7.5 log CFU/g。在亚致死温度范围上限对受大肠杆菌O157:H7污染的牛肉加热5分钟，可提高大肠杆菌O157:H7在随后慢煮过程中的存活率。
