Enhanced degradation of α-chitin materials prepared from shrimp processing byproduct and production of N-acetyl-d-glucosamine by thermoactive chitinases from soil mesophilic fungi

Abstract

Soil isolates of mesophilic Penicillium monoverticillium CFR 2, Aspergillus flavus CFR 10 and Fusarium oxysporum CFR 8 were cultivated in solid state fermentation (SSF) using wheat bran solid medium supplemented with α-chitin in order to produce chitinolytic enzyme. Under SSF cultivation, maximum enzymes (U/g IDS) production was 41.0 (endo-chitinase) and 195.4 (β-N-acetylhexosaminidase) by P. monoverticillium, 26.8 (endo-chitinase) and 222.1 (β-N-acetylhexosaminidase) by A. flavus and 13.3 (endo-chitinase) and 168.3 (β-N-acetylhexosaminidase) by F. oxysporum after 166h of incubation. The crude endo-chitinase and β-N-acetylhexosaminidase derived from A. flavus and F. oxysporum revealed optimum temperature at 62±1°C, but the enzymes from P. monoverticillium showed optimum temperature at 52±1°C for maximum activity. Several fold increase in endo-chitinase and β-N-acetylhexosaminidase activities in the crude enzymes preparation was achieved after concentrating with polyethylene glycol. The concentrated crude chitinases from P. monoverticillium, A. flavus and F. oxysporum, respectively yielded 95.6, 96.6 and 96.1mmol/l of N-acetyl-D: -glucosamine (GlcNAc) in 48h of reaction from colloidal chitin. While, the crude enzyme preparations of P. monoverticillium, A. flavus and F. oxysporum produced 10.11, 6.85 and 10.7mmol/l of GlcNAc respectively, in 48h of reaction from crystalline α-chitin. HPLC analysis of colloidal chitin hydrolysates prepared with crude chitinases derived from P. monoverticillium, A. flavus and F. oxysporum revealed that the major reaction product was monomeric GlcNAc (~80%) and a small amount of (GlcNAc)(4) (~20%), indicating the potential of these enzymes for efficient production of GlcNAc from α-chitin.