OCCURRENCE OF A HIGHLY HEAT-SENSITIVE SPORE SUBPOPULATION OF BACILLUS-COAGULANS STCC-4522 AND ITS CONVERSION TO A MORE HEAT-STABLE FORM

The profile of the survival curves, at different heating temperatures, of B. coagulans STCC 4522 sporulated at 52 degrees C has been studied , focusing on the early moments of treatment. A highly heat-sensitive spore subpopulation that includes more than 90% of the total spore pop ulation has been found. This heat-sensitive spore fraction was inactiv ated after 2 s of treatment at 111 degrees C. Its heat resistance was as much as 200-fold lower than that of the heat-resistant spore fracti on (D-111 degrees C of 0.01 min for the heat-sensitive spore fraction compared with D-111 degrees C of 2 min for the heat-resistant fraction ). The shape of the survival curve at 108.5 degrees C was modified aft er a sublethal heat shock at 80 degrees C for 3.5 h, resulting in a st raight-line survival curve. The temperature of treatment also influenc ed the shape of the survival curves. The conversion of the highly heat -sensitive spore subpopulation to a more heat-stable form is discussed .