Differences between xylanases produced by Aspergillus FP-470 growing under normal (37 degrees C) and temperature stress conditions (45 degrees C) were evaluated. Fungal growth at 45 degrees C was seriously affected. However, the xylanase specific activity was 2.5 times higher than that produced at 37 degrees C. Optimum pH and temperature were 6.5, 80 degrees C and 4.3, 50 degrees C for the xylanases produced at 37 degrees C and 45 degrees C, respectively. Electrophoresis showed that a more complex xylanolytic system was produced at 37 degrees C. Stress induced by temperature produced a decrease in the number of extracellular xylanases released by fungi, but increased the production of some xylanases, possibly essential for growth under stress conditions.

Aims: To evaluate and compare the sensitivity of Exo-PG production and kinetic parameters of Aspergillus flavipes FP-500 to oxygen transfer condition in shake flasks and bioreactor. Methods and Results: Aspergillus flavipes FP-500 was grown on pectin as carbon source in shake flasks and bioreactor at different oxygen transfer conditions. The volumetric coefficient of oxygen transfer (k L a) was modified by changing both, the flask size/medium volume ratio and the agitation speed. Higher biomass concentration, Exo-PG activity, maximum specific growth rate and yield coefficient were obtained in bioreactor at higher k L a value. A strong correlation was found between biomass, Exo-PG activity and growth-associated product coefficient to k L a in bioreactor but does not in shake flasks. The mathematical model provided a good description of growth, pectin consumption and Exo-PG production in submerged batch cultures carried out in bioreactor. Conclusions: Biomass concentration, Exo-PG activity and their kinetics of Aspergillus flavipes FP-500 were strongly influenced by oxygen transfer condition and cultivation system. Significance and Impact of Study: The production of enzymes by fungal fermentation is strictly aerobic and understanding the influence of oxygen transfer condition on the production kinetic is of vital importance in order to design, optimize and translate bioprocesses to industrial scale.

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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 pectin-degrading 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

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