Polygalacturonases of Aspergillus flavipes FP-500: A kinetic analysis of batch culture systems based on unstructured models

Pectin is a widespread complex heteropolysaccharide contained in plants cell wall. The hydrolysis of this natural-occurring polymer is an important process both in food industry and pectin-rich wastewater treatment. Although pectindegrading enzymes have been produced classically by microbial mold strains, production kinetics of the involved endo- and exo-pectinolytic enzymes is still a challenge in industrial microbiology. In order to assess the pectinases production kinetics, the strain Aspergillus flavipes FP-500 was grown in batch cultures using pectin, glucose or galacturonic acid as limiting substrates. Unstructured models were useful for describing the experimental behavior, and for estimating the kinetic parameters associated to the Logistic, Monod and Luedeking-Piret models. Our results pointed out that the exopolygalacturonases production is basically non-growth associated, suggesting an inducible nature for some exo-isoenzymes and endopolygalacturonases, even if some constitutive activity is postulated. Besides, to identify the combined effect of carbon source and pH on polygalacturonases production, several experiments were developed at different pH culture conditions. Exopectinases produced on glucose were inhibited by culture media acidification, while on galacturonic acid these enzymes are produced mainly at pH values of 5.0 or higher. Exopectinases production on pectin was not importantly affected by the established pH values during the culture. Endopectinases were produced basically at acidic conditions on pectin, but growth on galacturonic acid showed a strong inducing effect on endopectinases at pH 5.0.