Pectinase production profile of Aspergillus foetidus in solid state cultures at different acidities

Abstract

Solid-state cultures of a pectinase-producing fungus (Aspergillus foetidus NRRL 341) were performed under different acidic conditions. Glass bottles containing 5 g of wheat bran and 7.5 mL of 0.2, 0.3, 0.4, or 0.5 N HCl were autoclaved (15 min, 121°C), inoculated with a spore suspension appropriately diluted to achieve an initial concentration of 4 × 10⁴ spores per gram of wet substrate (with a 60 % humidity, on wet basis) and incubated at 30°C. Time course of pH and of different pectinase activities were determined in culture extracts. Total pectinase activity (TPA), expressed in terms of viscosimetric units per gram of wet substrate (VU.g⁻¹), was affected by the initial culture acidity. The higher the HCl concentration used, the higher the TPA achieved, but after longer cultivation times. On the other hand, when 0.5 HCl was used, no fungal growth was observed. Nevertheless, enzyme productivity increased with culture acidity. When 0.4 HCl was used, TPA reached its maximum after 36 h of cultivation (2,535 VU.g⁻¹). With 0.2 and 0.3 N HCl, TPA was the highest at 24 h (733 VU.g⁻¹) and at 30 h (1,860 VU.g⁻¹) respectively. The composition of the pectinase pool was also affected by culture acidity. The higher the acidity, the lower the pectinesterase activity and the higher both the polymethylgalacturonate lyase and polygalacturonase activities.