THE EFFECT OF AGE ON THE THERMAL-RESISTANCE OF ARTHROCONIDIA FROM CHRYSOSPORIUM INOPS

Food-borne members of the genus Chrysosporium have been isolated relat ively infrequently. The heat resistance of arthroconidia of the xeroph ilic fungus, Chrysosporium inops Carmichael, was determined in 0.1% pe ptone at 66 degrees C. The survival curve was sigmoid in shape. The in itial lag period was due to the chains of arthroconidia. Thermal inact ivation occurred when one viable conidium was left per chain. The pres ence of chains of arthroconidia was confirmed with the cryo scanning e lectron microscope. The decimal reduction times were obtained from the regression line of the linear death phase for the heat-sensitive spor es. The decimal reduction time (D-66) increased with increasing spore age. It was 1.67 min for 3-week-old spores, 1.95 min for 4-week-old sp ores and 5.49 min for 6-week-old spores. The older spores could recove r from thermal death if they were given sufficient: time. There was a significant increase in D-66 value for 6-week-old spores from 3.97 min to 5.49 when the counts were obtained after 14 d incubation (compared to counts after incubation for 10 d). This effect was not seen for th e 3- and 4-week-old spores. There was a small population of heat-resis tant spores. The initial population of arthroconidia was greater than log 7 cfu ml(-1). After heating for 1 h at 66 degrees C approximately log 2.2 cfu ml(-1) survived. These survivors represented approximately 0.001% of the original population.