Production, Optimisation and Partial Characterisation of Enzymes from Filamentous Fungi Using Dried Forage Cactus Pear as Substrate

Purpose The forage cactus pear (Opuntia spp. and Nopalea spp.) has been sub-utilised, mostly, for ruminant feed during long periods of drought. In this study, Nopalea cochenillifera was investigated as an alternative substrate for the production of xylanases and beta-glucosidases by Aspergillus niger and Rhizopus sp. Methods The solid-state fermentation of N. cochenillifera by Aspergillus niger and Rhizopus sp. were optimised for xylanases and beta-glucosidases production using a central composite face-centered (CCF) experimental design and response surface methodology (RSM), considering the variables water activity, temperature and time. The enzymes obtained were also evaluated for their pH, temperature and storage stability. Results The theoretical optimum cultivation conditions were an initial water activity of 0.865 at 30 degrees C for 72 h. The equivalent enzymatic activities (U g(-1)) obtained were 355.56 (A. niger xylanase), 3456.91 (A. niger beta-glucosidase), 204.57 (Rhizopus sp. xylanase) and 1630.07 (Rhizopus sp. beta-glucosidase). The obtained enzymes presented good stability (similar to 80%) at <60 degrees C and pH values from 4.0 to 7.0. Conclusion The forage cactus is a potential alternative for microbial cultivation instead of synthetic substrates of elevated costs.