Effects of carbohydrates, proteins, and bacterial cells in the heating media on the heat resistance of Clostridium sporogenes.

It is well known that the heat resistance of bacterial spores is influenced markedly by the nature of the medium in which the spores are heated. This fact is an important problem relating to the practical sterilization in bacteriology and in the food industry. Hence voluminous data on the heat resistance of Clostridium botulinum and Clostridium porogenes in various kinds of foods or food juices have been published (Townsend et al., 1938; Reed et al., 1951; Reynolds et al., 1952). From these data, it can be easily pointed out that the resistance value of a strain in a food is larger than that in phosphate buffer, whereas in another food the resistance value of the same strain is smaller than that in neutral phosphate buffer. Although the pH of the heating media has a marked influence on the thermal death rate of bacteria, it appears that the cause of such a difference in resistance values of a strain cannot be attributed wholly to the variation of pH values of the foods (Sognefest et al., 1948). In fact, there are evidences that some of the ingredients of food might exert a protective effect or a death accelerating effect for the organism during the heating. Weiss (1921) reported that the longer survival time was obtained when the spores of C. botulinum were suspended and heated in the foods with the higher sugar concentration. The similar protective effect of sugars on the bacterial spores has been demonstrated by Anderson et al. (1949) and Sugiyama (1951). Murray and Headlee (1931) found that the presence of peptone in the heating medium had shown sometimes a protective effect for the spores of C. tetani. Recently, Kawai and Tanaka (1952) have shown that several kinds of higher molecular substances, such as gelatin, starch, gum arabic, and alginic acid, have the protective effects for the spores of Bacillus mesentericus and Bacillus brevis. The test organisms used by these workers are relatively less resistant than the most resistant food spoilage bacteria, and the kinds of the substances tested on each strain are rather limited. Thus it seemed important to study the effects of various substances on the most resistant strain. Using the spores of Cameron's putrefactive anaerobe 3679 (Clostridium sporogenes, ATCC 7955), the effects of various carbohydrates, proteins, and bacterial cells were studied. In the previous papers Amaha (1952a,b, 1953) has clearly indicated that the thermal death time of spores of certain strains is influenced markedly by the nature of the recovery media. In general the more favorable was the nature of a medium for the development of heated spores, the longer was the survival time. Hence, it should be considered that the substances added in the basal heating medium have the two stages in their action to the spores; the first, during the heating time, and the second, after the substances were transferred in the subculture medium. In this paper an attempt was made to distinguish the two effects, i.e., the first effect, a true protection, and the second effect, a false protection, of each of substances tested.