The dry-heat resistance of Bacillus subtilis var. niger spores located in or on various materials was determined as D and z values in the range of 105 through 160 C. The systems tested included spores located on steel and paper strips, spores located between stainless-steel washers mated together under 150 inch-lb and 12 inch-lb of torque, and spores encapsulated in methylmethacrylate and epoxy plastics. D values for a given temperature varied with the test system. High D values were observed for the systems in which spores were encapsulated or under heavy torque, whereas lower D values were observed for the steel and paper strip systems and the lightly torqued system. Similar z values were obtained for the plastic and steel strip systems (zD = 21 C), but an unusually low z for spores on paper (zD = 12.9 C) and an unusually high z for spores on steel washers mated at 150 inch-lb of torque (zD = 32 C) were observed. The effect of spore moisture content on the D value of spores encapsulated in water-impermeable plastic was determined, and maximal resistance was observed for spores with a water activity (aw) of 0.2 to 0.4. Significantly decreased D values were observed for spores with moisture contents below aw 0.2 or above aw 0.4. The data indicate that the important factors to be considered when measuring the dry heat resistance of spores are (i) the initial moisture content of the spore, (ii) the rate of spore desiccation during heating, (iii) the water retention capacity of the material in or on which spores are located, and (iv) the relative humidity of the system at the test temperature.
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机译:枯草芽孢杆菌变种的耐干热性。将位于各种材料之中或之上的尼日尔孢子的D和z值确定为105至160C。测试的系统包括位于钢和纸条上的孢子,位于不锈钢垫圈之间的孢子,它们在150英寸磅的压力下配合在一起和12英寸-磅的扭矩,并将孢子包裹在甲基丙烯酸甲酯和环氧树脂塑料中。给定温度的D值随测试系统而变化。对于包裹有孢子或在大扭矩下的系统,观察到较高的D值,而对于钢带和纸条系统以及小扭矩的系统,观察到较低的D值。对于塑料和钢带系统,z值相似(zD = 21 C),但纸上孢子的z值异常低(zD = 12.9 C),而在150英寸磅的钢垫圈上,孢子的z值异常高。观察到最大扭矩(zD = 32 C)。确定了孢子水分含量对包裹在不透水塑料中的孢子的D值的影响,并且观察到水分活度(aw)为0.2至0.4的孢子具有最大的抵抗力。对于水分含量低于 a em> w 0.2或高于 a em> w 0.4的孢子,D值显着降低。数据表明,在测量孢子的干耐热性时要考虑的重要因素是:(i)孢子的初始水分含量;(ii)加热过程中孢子的干燥速率;(iii)保水能力。孢子所在或之上的材料,以及(iv)测试温度下系统的相对湿度。
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