The stability of pectolytic enzymes in sulphite liquor in relation to breakdown of sulphited strawberries

Abstract

Abstract The stability of pectate and pectin depolymerising enzymes produced by Mucor piriformis, Rhizopus sexualis, R. stolonifer, Botrytis cinerea, Aureobasidium pullulans, Trichosporon pullulans and Cryptococcus albidus var. albidus in sulphite liquor was studied in relation to the breakdown of sulphited fruit. Marked breakdown of fruit occurred only when pectolytic activity could be detected in the liquor for more than 2 weeks using a viscometric assay. Of the fungi tested Rhizopus spp. produced enzymes which were most stable in sulphite liquor. For each of the Mucor and Rhizopus species tested, the stability of polygalacturonases in sulphite liquor was very similar for extracts of infected fruit and culture filtrates. The rapid decrease in polygalacturonase activity for both systems in the first 48 h contrasted with a slower inactivation where infected tissue was used. The reasons for this are discussed and it is suggested that sulphite labile (= acid labile) and sulphite stable (= acid stable) forms of the polygalacturonases are present.