HEAT-RESISTANCE OF ASCOSPORES OF BYSSOCHLAMYS-NIVEA IN MILK AND CREAM

Byssochlamys nivea strains of rather varying origin used for heat inactivation experiments were cultured for 28 days at 30-degrees-C on malt extract agar, since under these conditions the highest degree of heat resistance of the ascospores was obsered. Inactivation was performed in steel capillary tubes to obtain reproducible results under experimental conditions comparable to those prevailing in practice. An inactivation temperature of 92-degrees-C proved to be most practical. Decimal reduction times for the individual strains at this temperature in Ringer's solution varied between 1.3 and 2.4 s. In the temperature range studied, inactivation of ascospores in UHT milk (1.5% w/w fat content) and cream (10% w/w fat content) has not been found to differ significantly from that in Ringer's solution. Homogenization of milk as applied in practice did not affect heat inactivation of ascospores. Assuming the most unfavorable conditions (50 ascospores/1 and using the most heat-resistant strain) the following relations between the level of infected 500 g packages were calculated: 1 of 10(6) packs infected; 24 s at 92-degrees-C; 1 of 10(3) packs infected; 16.5 s at 92-degrees-C; 1 of 10(2) packs infected, 14 s at 92-degrees-C.