Salt and nitrogen amendment and optimization for cellulase and xylanase production using dilute acid hydrolysate of distillers' dried grains with solubles (DDGS) as the feedstock.

Abstract

Distillers' dried grains with solubles (DDGS) is a by-product of dry-mill corn ethanol production comprising a high nutritional value due to residual fiber, protein, and lipid contents. The fiber content of DDGS is high enough to be considered a valuable source for the production of hydrolytic enzymes, such as cellulase and xylanases, which can be used for hydrolysis of lignocellulosic feedstock during ethanol production. The DDGS-based medium prepared after acid hydrolysis provides adequate sugars for enzyme production, while additional macronutrients, such as salts and nitrogen sources, can enhance the enzyme production. Therefore, this study was undertaken to evaluate the effect of salts (KH2PO4, CaCl2·2H2O, MgSO4·7H2O, FeSO4·7H2O, CoCl2·6H2O, and MnSO4·H2O), peptone, and yeast extract on enzyme secretion by four different Aspergillus niger strains and to optimize the nitrogen source for maximum enzyme production. Yeast extract improved the cellulase production (0.38IU/ml) for A. niger (NRRL 1956) as compared to peptone (0.29IU/ml). However, maximum cellulase productions of 0.42IU/ml and 0.45IU/ml were obtained by A. niger (NRRL 330) and A. niger (NRRL 567), respectively, in presence of ammonium sulfate. The optimized nitrogen amounts resulted in a significant increase in the cellulase production from 0.174 to 0.63IU/ml on day 9 of the fermentation with A. niger (NRRL 330). The composite model improved both cellulase and xylanase production. In conclusion, the optimization of all three nitrogen sources improved both cellulase and xylanase production in the DDGS-based media.