1 0 0 0 OA 種麹乳酸菌の熱殺菌について
Commerically available take-koji, sporulated koji and used as the seed for koji making, is sometimes regarded as one of the sources of infection by lactic acid bacteria in sake brewing. To sterilize these contaminants by heat and, at the same time, to minimize the heat inactivation of Aspergillus oryzae conidiospores, the heat drying conditions of take-koji have been examined.1) The heat resistance of lactic acid bacteria was different depending on species and cultural age : Leusonostoc mesenterioides B-95 was more stable than Lactobacillus casei B-83,and in regard to the same species, the cells harvested from the culture at the maximum groeth were most stable (see Fig.1,Fig.2 and Table1). Therefore, Leuc. mesenteroides B-95 cells at the maximum growth was used for determination of the drying conditions.2) The patterns of thermal death of the test organisms on the surface of steamed rice or on tane-koji seemed to be related to the patterns of heat drying of solid materials : the velocity of thermal death in the constent rate period of drying was more rapid than that in the falling rate period. In the latter period, the spores of Asp. oryzae became very stable (see Table 2). In the drying of steamed rice, the critical moisture content was in the range from 0.15 to 0.20 H_2O per g dry stock.According to these results, a two steps method for drying of tane-koji, namely low temperature drying at constant rate period succeeded by high temprature drying at falling rate period, has been proposed. For example, in the case of the low temperaturedrying at 40℃(wet-bulb temperature)(t_w) : 28℃) for 3 hours and high temperature dryig at 60℃(t_w : 32℃) for 12 hours, the concentration of Leuc. mesenteroides diminished to 10^<-8> times the initial. Under these conditions, the rate of inactivtion of Asp. oryzae spores was only 10 per cent.