Β-glucosidase production of two different Aspergillus strains

Β-glucosidase has an important role in cellulose degradation by cleaving the cellobiose to glucose units. Supplementation of Trichodermacellulase with exogenous β-glucosidase is needed to prevent the inhibition effect of cellobiose on exoglucanases and endoglucanases.Production of β-glucosidase by Aspergillus niger and Aspergillus phoenicishas been investigated under different fermentations. Both strains were appropriate for enzyme production at high level under the applied conditions. Cultivation of A. phoenicison Mandels' medium containing a complex nitrogen source has resulted in a higher β-glucosidase activity than on Vogel's medium. In an air-lift fermenter A. phoenicis grew in the shape of beads with 1.41 IU g–1 cell-associated enzyme activity. The fungal pellets can be used as in situ immobilized enzyme preparation. A. niger produced extracellular β-glucosidase at the level of 2.1 IU ml–1 in stirred-tank fermenter with a yield of 210 IU g–1 glucose and productivity of 21.8 IU l–1 h–1

Use of hemicellulose hydrolysate for beta-glucosidase fermentation

Hydrolysis of cellulose by Trichoderma cellulases often results in a mixture of glucose, cellobiose, and low-mol-wt cellodextrins. Cellobiose is nonfermentable for most yeasts, and therefore it has to be hydrolyzed to glucose by beta-glucosidase prior to ethanol fermentation. In the present study, the beta-glucosidase production of one Penicillium and three Aspergillus strains, which were previously selected out of 24 strains, was investigated on steam pretreated willow. Both steam-pretreated willow and hemicellulose hydrolysate, released during steam explosion of willow, were used as carbon sources. Reference cultivation runs were performed using prehydrolyzed Solka Flee and glucose. The four strains were compared with Trichoderma reesei regarding sugar consumption and beta-glucosidase production. Aspergillus niger and Aspergillus phoenicis proved to be the best enzyme producers on hemicellulose hydrolysate. The maximum beta-glucosidase activity, 4.60 IU/mL, was obtained when A. phoenicis was cultivated on the mixture of hemicellulose hydrolysate and steam-pretreated willow. The maximum yield of enzyme activity, 502 IU/g total carbohydrate, was obtained when Aspergillus foetidus was cultivated on the hemicellulose hydrolysate