Optimization of the fermentation parameters to maximize the production of cellulases and xylanases using DDGS as the main feedstock in stirred tank bioreactors

Abstract

Lignocellulolytic enzymes such as cellulase and xylanases are needed on the industrial scales for low-cost production of biofuels and the other value-added products from lignocellulosic biomass such as distillers' dried grains with solubles (DDGS). Optimization of fermentation variables such as agitation, aeration, and inoculum size for fungal enzyme production by submerged fermentation can enhance the enzyme production levels. Therefore, this research focused on the statistical optimization of fungal inoculum size (1–10%), aeration (0.5-2vvm) and agitation rates (100–500rpm) through response surface methodology (RSM) to obtain highest amounts of cellulases and xylanases. Aspergillus niger (NRRL 330) was grown in dilute acid treated DDGS supplemented with peptone, yeast extract, and ammonium sulfate in benchtop bioreactors to produce these enzymes. The optimal fermentation results were determined to be 6.5% inoculum size, 310 rpm agitation rate and 1.4 vvm aeration, which revealed increases of cellulase activity from 0.6 to 0.82 IU/ml and xylanase activity from 3.99 to 52.76 IU/ml after optimization. The results prove the need for optimization of culture conditions such as aeration, agitation and inoculum size for higher production of hydrolytic enzymes by A. niger using DDGS as the main feedstock.