Chung Hyun-Jung, Wang Shaojin, Tang Juming
Department of Biological Systems Engineering, Washington State University, Pullman, Washington 99164-6120, USA.
J Food Prot. 2007 Apr;70(4):851-9. doi: 10.4315/0362-028x-70.4.851.
The purpose of this study was to investigate the influence of heat transfer on measured thermal inactivation kinetic parameters of bacteria in solid foods when using tube methods. The bacterial strain selected for this study, Escherichia coli K-12, had demonstrated typical first-order inactivation characteristics under isothermal test conditions. Three tubes of different sizes (3, 13, and 20 mm outer diameter) were used in the heat treatments at 57, 60, and 63 degrees C with mashed potato as the test food. A computer model was developed to evaluate the effect of transit heat transfer behavior on microbial inactivation in the test tubes. The results confirmed that the survival curves of E. coli K-12 obtained in 3-mm capillary tubes were log linear at the three tested temperatures. The survival curves observed under nonisothermal conditions in larger tubes were no longer log linear. Slow heat transfer alone could only partially account for the large departures from log-linear behavior. Tests with the same bacterial strain after 5 min of preconditioning at a sublethal temperature of 45 degrees C revealed significantly enhanced heat resistance. Confirmative tests revealed that the increased heat resistance of the test bacterium in the center of the large tubes during the warming-up periods resulted in significantly larger D-values than those obtained with capillary tube methods.
本研究的目的是探讨在使用试管法时，传热对固体食品中细菌热失活动力学参数测量值的影响。本研究选用的细菌菌株大肠杆菌K-12，在等温试验条件下已表现出典型的一级失活特征。以土豆泥为测试食品，在57、60和63摄氏度的热处理中使用了三种不同尺寸（外径分别为3、13和20毫米）的试管。开发了一个计算机模型来评估传热行为对试管中微生物失活的影响。结果证实，在三个测试温度下，在3毫米毛细管中获得的大肠杆菌K-12存活曲线呈对数线性。在较大试管的非等温条件下观察到的存活曲线不再是对数线性的。仅缓慢传热只能部分解释与对数线性行为的较大偏差。在45摄氏度的亚致死温度下预处理5分钟后，对同一菌株进行的测试显示耐热性显著增强。验证性测试表明，在升温期间，大试管中心测试细菌的耐热性增加导致D值显著大于毛细管法获得的D值。
