Production, characterization and application of a thermostable polygalacturonase of a thermophilic mould Sporotrichum thermophile Apinis

Abstract

The production of polygalacturonase (PGase) by Sporotrichum thermophile Apinis in stirred submerged fermentation (SmF) was high in comparison with that in static conditions. Yeast extract (0.25%) and citrus pectin (2%) at pH 7.0 and 45 °C supported a high enzyme production in flasks agitated at 200 rpm. An overall 1.75-fold enhancement in PGase production was achieved as a result of optimization. The enzyme was optimally active at pH 7.0 and 55 °C, and exhibited t 1/2 of 4 h at 65 °C. The K m and V max values of the enzyme (for pectin) were 0.416 mg ml −1 and 0.52 μmol mg −1 min −1, respectively. The PGase activity was stimulated by Mn 2+ and Fe 2+, but inhibited strongly by Mg 2+, and slightly by Tween 80 and Triton X-100. Among the additives tested, β-mercaptoethanol exerted a strong inhibitory effect, suggesting a critical role of disulphide linkages in maintaining a suitable conformation of the enzyme. An increase in the yield of banana, grape and apple juices was recorded due to the treatment of fruit pulps with the mixture of enzymes (pectinase, xylanases and cellulase) of S. thermophile as compared to that with only pectinase. The yield of fruit juices did not increase with enhanced titre of cellulase in the enzyme mixture.