Batch and Pulsed Fed-Batch Cultures of Aspergillus flavipes FP-500 Growing on Lemon Peel at Stirred Tank Reactor.

Aspergillus flavipes FP-500 grew up on submerged cultures using lemon peel as the only carbon source, developing several batch and pulsed fed-batch trials on a stirred tank reactor. The effect of carbon source concentration, reducing sugar presence and initial pH on exopectinase and endopectinase production, was analyzed on batch cultures. From this, we observed that the highest substrate concentration favored biomass (X max) but had not influence on the corresponding specific production (q p) of both pectinases; the most acid condition provoked higher endopectinase-specific productions but had not a significant effect on those corresponding to exopectinases; and reducing sugar concentrations higher than 1.5 g/L retarded pectinase production. On the other hand, by employing the pulsed fed-batch operation mode, we observed a prolonged growth phase, and an increase of about twofold on endopectinase production without a significant raise on biomass concentration. So, pulsed fed-batch seems to be a good alternative for obtaining higher endopectinase titers by using high lemon peel quantities without having mixing and repression problems to the system. The usefulness of unstructured kinetic models for explaining, under a theoretic level, the behavior of the fungus along the batch culture with regard to pectinase production was evident.

Use of fruit residues for pectinase production by Aspergillus flavipes FP-500 and Aspergillus terreus FP-370.

AIMS: Utilization of fruit residues for pectinase production by two Aspergillus strains for recognizing the effects of some factors during fermentation and describing enzyme production kinetics. METHODS AND RESULTS: Pectinase production on several fruit residues was compared. The effects of three factors on the production of several pectinases were evaluated by a full factorial 2(k) experimental design. Higher activities were obtained on lemon peel. In both strains, acidic pH values and high carbon source concentration favoured exopectinase and endopectinase production, while higher pH values and low carbon source concentration promoted pectin lyase and rhamnogalacturonase production. Unstructured mathematical modelling provided a good description of pectinase production in a submerged batch culture. CONCLUSIONS: Fruit residues were very good substrates for pectinase production, and Aspergillus strains used showed a promising performance in submerged fermentation. Mathematical modelling was useful to describe growth and pectinase production. SIGNIFICANCE AND IMPACT OF THE STUDY: Lemon peel can be used as a substrate to obtain high pectinase titres by Aspergillus flavipes FP-500 and Aspergillus terreus FP-370. The factors that contributed to improve the yield were identified, which supports the possibility of using this substrate in the industrial production of these enzymes.

Thermostable xylanases produced at 37 degrees C and 45 degrees C by a thermotolerant Aspergillus strain.

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.