Heat stability of endo‐polygalacturonases of Mucoraceous spoilage fungi in relation to canned fruits

Abstract

Abstract The heat resistance of endo‐polygalacturonase (endo‐PG) of the strawberry spoilage fungi, Rhizopus sexualis, R. stolonifer and Mucor piriformis , was compared to that of isolates of R. arrhizus, R. stolonifer and R. oryzae known to cause breakdown of canned apricots. All species produced endo‐PGs in culture medium which showed marked heat tolerance and a bimodal heat stability. Heating for 10 min at temperatures between 30–120°C indicated that maximum inactivation occurred at 50–60°C. Stability increased from 70°C to 100°C and then declined, but in some cases activity remained even after heating at 120°C for 10 min. Similar trends in heat resistance were recorded for endo‐PGs in infected tissue of apricot, peach, tomato and cherry fruits, whereas those in infected tissue of strawberry, raspberry and plum were rapidly inactivated at all temperatures above 40°C. The possible reasons for differences between fruits are discussed.