Xylose-Enriched Ethanol Fermentation Stillage from Sweet Sorghum for Xylitol and Astaxanthin Production

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.

Sugarcane Bagasse-Based Ethanol Production and Utilization of Its Vinasse for Xylitol Production as an Approach in Integrated Biorefinery

“…In this process, separate streams of ethanol and xylitol resulted. Ethanol obtained in this study was within the same range as a previous study with a similar design using sweet sorghum juice and bagasse [32]. Increased quantities of xylitol were obtained in this study, compared with less than 5 g/L obtained from the stillage (vinasse) of the study employing Candida mogii.…”

“…Nitrogen source supplementation may be necessary as available nitrogen in the hydrolysate could be depleted in the ethanol fermentation stage. The vinasse was used without any treatment or detoxification, although Candida mogii fermentation in concentrated stillage (vinasse) after ethanol fermentation from sweet sorghum juice and bagasse showed the necessity of detoxifying the stillage [32].…”

From Aquaculture to Aquaculture: Production of the Fish Feed Additive Astaxanthin by Corynebacterium glutamicum Using Aquaculture Sidestream

“…The yeast P. rhodozyma produced about 130 mg L −1 astaxanthin after 120 h by direct fermentation of food wastes (1.08 mg L −1 h −1 ) [ 116 ]. On stillage media derived from bagasse-based ethanol fermentation of S. cerevisiae , about 18 mg L −1 astaxanthin accumulated within one week of fermentation (0.10 mg L −1 h −1 ) [ 117 ]. Both sidestreams are much richer as compared to the AQ used in this study.…”

Pretreatment and enzymatic hydrolysis optimization of lignocellulosic biomass for ethanol, xylitol, and phenylacetylcarbinol co-production using Candida magnoliae

“…A yeast-malt medium supplemented with 5 g/L xylose (YMX) ( Stoklosa et al, 2019 ) was used as a pre-seed and seed cultivation medium for microbial propagation. The glycerol stock of C. magnoliae TISTR 5664 was cultivated in the YMX medium at 30°C and 200 rpm for 24 h ( Nunta et al, 2018 ) before using it as seed inoculum.…”