Inactivation of pectic lyases by light exposure in model systems and fresh-cut apple

UV-C light exposure caused the inactivation of pectin lyases from Aspergillus japonicus and pectate lyase from apple under non-thermal conditions. Samples exposed to 20 W m(-2) UV-C light showed D(L) values, defined as the time needed for 90% enzyme activity reduction, around 20 min. However, an initial activation phase was observed for fungin pectin lyase, while UV-C light resistant forms of pectate lyase were identified in apple. Lyase inactivation occurred as a consequence of enzyme cleavage into fragments without catalytic activity having MW around 5 kDa. Fresh-cut apple slices exposed for a few minutes to UV-C light resulted significantly firmer than the untreated ones during 4 days of refrigerated storage, reasonably due to the decrease in activity of both endogenous and microbial lyases on the surface of the wound apple tissue. Industrial relevance: UV-C light blanching allows to non-thermally increase the enzymatic stability of the surface of fresh-cut fruit and vegetables.