Statistical optimization of solid state fermentation conditions for the enhanced production of thermoactive chitinases by mesophilic soil fungi using response surface methodology and their application in the reclamation of shrimp processing by-products

Abstract

The mesophilic strains Aspergillus flavus CFR 10 and Fusarium oxysporum CFR 8 are potent producers of extracellular thermoactive chitinases (endo-chitinase and β-N-acetylhexosaminidase). Chitinases have a wide range of applications in many areas including reclamation of seafood processing chitinous by-products. In the present study, the interactive effects of four fermentation conditions on thermoactive chitinase production by solid state fermentation (SSF) using commercial wheat bran (CWB) was investigated employing response surface methodology (RSM). Further, these chitinases were applied for the preparation of N-acetyl chitooligosaccharides from shrimp chitin. Statistical optimization resulted in the production (unit/g initial dry substrate, U/g IDS) of 19.8 endo-chitinase and 649.0 β-N-acetylhexosaminidase activity by A. flavus CFR 10, and 17.5 endo-chitinase and 319.9 β-N-acetylhexosaminidase activity by F. oxysporum CFR 8. Activity of crude endo-chitinase and β-N-acetylhexosaminidase were found to be optimum at 62 ± 1 °C in a wide pH range. Hydrolysis of colloidal chitin with crude chitinases produced the maximum N-acetyl chitooligosaccharides yield (mmol/l) of 10.4 ± 0.28 at 6 h and 10.2 ± 0.01 at 30 h post-reaction initiation, respectively, by the enzymes of A. flavus CFR 10 and F. oxysporum CFR 8. HPLC analysis revealed the presence of N-acetyl chitooligosaccharides with N-acetyl chitotriose as the main end product of the colloidal chitin hydrolysis. These results indicate the potential of mesophilic A. flavus CFR 10 and F. oxysporum CFR 8 in the production of thermoactive chitinases employing the economical SSF process using CWB as an ideal substrate, as well as the potential of these chitinases for the reclamation of abundant shrimp processing by-products and production of defined N-acetyl chitooligosaccharides.