Tannase production through solid-state fermentation of Shorea robusta deoiled seed cake: an industrial biomass using Aspergillus flavus TF-8 for potential application in gallic acid synthesis

In the present study, utilization of Sal ( Shorea robusta ) deoiled seed cake (DOC), a forest industrial biomass residue as substrate for solid-state fermentation (SSF) was attempted for the microbial growth and production of industrially useful enzyme: tannase. Work was carried out to find the optimal conditions of SSF using Sal DOC as substrate for tannase production by exploiting the laboratory isolated Aspergillus flavus . Following optimization, further studies were undertaken to (a) scale up the SSF process for tannase production, (b) enzyme characterization, and (c) partial purification of tannase. Salt solution of pH 5.0 as moistening agent; substrate to moistening agent ratio of 1:1 (w/v); inoculums size, 10 7 spores/ml; inoculum age, 72 h; incubation temperature, 28 °C; and incubation time, 72 h, were found to be the best fermentation conditions. The supplementation of additional carbon and nitrogen sources did not stimulate the tannase production, indicating the presence of sufficient nutrients in Sal DOC. A maximum of 599 U/gds of enzyme production was reached under optimized conditions which could further be enhanced to 661U/gds (1.10-folds) under upscale SSF. The enzymatic properties of tannase revealed pH and temperature optima to be 5.5 and 60 °C, respectively. Partially purified tannase could successfully be applied for the enzymatic hydrolysis of Terminalia chebula (myrobalan) tannins for gallic acid production. These results show a sustainable approach for the utilization of this abundantly available Sal DOC biomass through solid-state fermentation for the production of an industrial and costly enzyme, tannase. The produced tannase has potential in the synthesis of gallic acid and may find suitable application in food and pharmaceutical industries. Graphical abstract