Production, purification and biochemical characterization of an exo-polygalacturonase from Aspergillus niger MTCC 478 suitable for clarification of orange juice.

Polygalacturonases (PG) represent an important member of pectinases group of enzymes with immense industrial applications. A fungal strain Aspergillus niger MTCC478 was used for the production of polygalacturonase both under submerged and solid-state fermentation condition. Further its production was optimized under solid-state fermentation condition with media comprising of wheat bran and tea extract. Purification of an exo-PG was achieved by acetone precipitation (60-90%) and CM-cellulose column chromatography revealing 15.28-fold purification with a specific activity of 33.47 U/mg protein and 1.2% yield. A relative molecular mass of purified PG was approximately 124.0 kDa. The pH and temperature optimum was found to be 4 and 50 °C, respectively. The k cat and K m value for degradation of PGA by the purified enzyme was found to be 194 s(-1) and 2.3 mg/mL, respectively. Cu(2+) was found to enhance the PG activity while Ag(+) completely inhibited the enzyme activity. The application of the purified PG in orange juice clarification was elucidated.