Ingram R, Hitchings E, Archer J, Gaze J E
Campden and Chorleywood Food Researh Association, Chipping Campden, Glouchestershire, UK.
Int J Food Microbiol. 2001 Jan 22;63(1-2):125-34. doi: 10.1016/s0168-1605(00)00465-7.
The aim of the present work was to investigate the effect of ethanol alone and in combination with low pH on the heat resistance of specific bacteria. The bacteria chosen are representative of heat resistant and heat sensitive pathogens (Bacillus cereus and Salmonella typhimurium) and of relatively heat resistant spoilage microorganisms (Lactobacillus delbrueckii). The chosen bacteria were treated at different temperatures ranging between 70 and 97 degrees C for B. cereus, 48 and 54 degrees C for S. typhimurium and 44 and 60 degrees C for L. delbrueckii, in media of different pH (3, 5 and 7) and ethanol content (0, 2.5, 5, 7.5 and 10%). Both factors proved to be very effective in reducing the heat resistance of the bacteria examined in this work. At pH 7, an increase in ethanol content up to 10% caused D values to decrease by up to 100-fold (S. typhimurium). A drop from pH 7 to pH 3 also caused up to a 100-fold reduction in the D values (S. typhimurium). For B. cereus the regression analysis of the log10 of the D value in relation to temperature, pH and ethanol content was used to produce a second order polynomial equation. The z values increased at decreasing pH and cells were more sensitive to ethanol at lower pH. For S. typhimurium the polynomial equation produced to describe the relationship between log10 of the D values and temperature and ethanol content was also a second order equation indicating that the relationship between z values and ethanol was non-linear. For L. delbrueckii, z values were independent of the ethanol content of the heating medium. Acid tolerance at 25 and 37 degrees C (L. delbrueckii and S. typhimurium) and acid adaptation (S. typhimurium) were also tested. L. delbrueckii was more ethanol and pH tolerant than S. typhimurium at heat treatment temperatures whilst S. typhimurium was more acid tolerant than L. delbrueckii at incubation temperatures (25 and 37 degrees C). Acid adaptation increased the tolerance of S. typhimurium to low pH at 25 degrees C but failed to improve its thermal resistance at 48 degrees C. In all bacteria used, the effects of pH and ethanol were more evident at lower treatment temperatures and therefore their significance becomes greater in view of reduced thermal processing and/or changes in product formulation.
本研究的目的是调查乙醇单独作用以及与低pH值联合作用对特定细菌耐热性的影响。所选用的细菌代表了耐热和热敏病原体（蜡样芽孢杆菌和鼠伤寒沙门氏菌）以及相对耐热的腐败微生物（德氏乳杆菌）。对于蜡样芽孢杆菌，将所选细菌在70至97摄氏度的不同温度下处理；对于鼠伤寒沙门氏菌，处理温度为48至54摄氏度；对于德氏乳杆菌，处理温度为44至60摄氏度，处理时使用不同pH值（3、5和7）和乙醇含量（0、2.5、5、7.5和10%）的培养基。事实证明，这两个因素在降低本研究中所检测细菌的耐热性方面都非常有效。在pH值为7时，乙醇含量增加至10%会使D值降低多达100倍（鼠伤寒沙门氏菌）。pH值从7降至3也会使D值降低多达100倍（鼠伤寒沙门氏菌）。对于蜡样芽孢杆菌，通过对D值的log10与温度、pH值和乙醇含量进行回归分析，得出了一个二阶多项式方程。随着pH值降低，z值增加，并且在较低pH值下细胞对乙醇更敏感。对于鼠伤寒沙门氏菌，用于描述D值的log10与温度和乙醇含量之间关系的多项式方程也是一个二阶方程，这表明z值与乙醇之间的关系是非线性的。对于德氏乳杆菌，z值与加热培养基中的乙醇含量无关。还测试了25摄氏度和37摄氏度下的耐酸性（德氏乳杆菌和鼠伤寒沙门氏菌）以及酸适应性（鼠伤寒沙门氏菌）。在热处理温度下，德氏乳杆菌比鼠伤寒沙门氏菌更耐乙醇和pH值变化，而在培养温度（25摄氏度和37摄氏度）下，鼠伤寒沙门氏菌比德氏乳杆菌更耐酸。酸适应性提高了鼠伤寒沙门氏菌在25摄氏度下对低pH值的耐受性，但未能提高其在48摄氏度下的耐热性。在所有使用的细菌中，pH值和乙醇的影响在较低处理温度下更为明显，因此鉴于热加工减少和/或产品配方变化，它们的重要性变得更大。
