Abstract
Developing integrated biorefineries requires the generation of high-value co-products produced alongside cellulosic ethanol. Most industrial yeast strains produce ethanol at high titers, but the small profit margins for generating ethanol require that additional high-value chemicals be generated to improve revenue. The aim of this research was to boost xylose utilization and conversion to high-value co-products that can be generated in an integrated biorefinery. Pretreated sweet sorghum bagasse (SSB) was hydrolyzed in sweet sorghum juice (SSJ) followed by ethanol fermentation. Ethanol was removed from the fermentation broth by evaporation to generate a stillage media enriched in xylose. Candida mogii NRRL Y-17032 could easily grow in non-detoxified stillage media, but a high xylitol yield of 0.55 g xylitol/g xylose consumed was achieved after recovered cells were resuspended in synthetic media containing supplemented xylose. Phaffia rhodozyma ATCC 74219 could be cultivated in non-detoxified stillage media, but astaxanthin generation was increased 4-fold (from 17.5 to 71.7 mg/L) in detoxified media. Future processing strategies to boost product output should focus on a two-step process where the stillage media is used as the growth stage, and a synthetic media for the production stage utilizing xylose generated from SSB through selective hemicellulase enzymes.
Highlights
As greater emphasis is placed on developing a sustainable bioeconomy, integrated biorefineries producing both biofuels and high-value co-products are essential to limit and reduce petroleum dependence
sweet sorghum bagasse (SSB) pretreated by the low-moisture anhydrous ammonia (LMAA) process could be subjected to enzymatic hydrolysis in sweet sorghum juice (SSJ) followed by ethanol fermentation
A high xylitol yield of 0.55 g xylitol/g xylose consumed could be achieved after C. mogii was cultivated for growth in non-detoxified stillage media with additional xylose supplementation followed by cell recovery and resuspension in synthetic media
Summary
As greater emphasis is placed on developing a sustainable bioeconomy, integrated biorefineries producing both biofuels and high-value co-products are essential to limit and reduce petroleum dependence. While biofuels from agricultural feedstocks can contribute to the overall liquid transportation fuel market, challenges remain for the development of integrated biorefineries due to economic constraints. Biorefineries for cellulosic ethanol production have yet to be widely commercialized due to wide-ranging challenges including feedstock supply [4], the handling of solids during pretreatment and enzymatic hydrolysis [5], and overall capital investment [6]. Like the corn ethanol industry, the generation of high-value co-products during cellulosic ethanol production can improve overall profitability of integrated biorefineries. The challenge is to identify the feedstock fraction for conversion and the type of co-product to generate
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