FUNGAL AND PLANT XYLOGLUCANASES MAY ACT IN CONCERT DURING LIQUEFACTION OF APPLES

Efficient enzymic degradation of cellulose in isolated cell wall mater ial of apples requires prior removal of its xyloglucan coating. In thi s study, raw and blanched apple fruit tissues were treated with pectin lyase and various (combinations of purified) cellulases. These experi ments confirmed that xyloglucanase activity is important for cellulose degradation in apple fruit tissue. Apart from this, it was observed t hat raw apple material disintegrated faster than blanched. Typically, the release of xyloglucan oligosaccharide XXXG from raw apple material was slower (relative to XXFG) when compared to that from blanched mat erial. The endogenous enzyme, xyloglucan endotransglycosylase (XET), i s probably responsible for these phenomena. It is hypothesised that XE T activity accelerates disintegration of apple tissue once its depolym erising mode is triggered by xyloglucan oligosaccharides released by e xogenous endoglucanases.