Optimization of xylitol production from xylose by a novel arabitol limited co-producing Barnettozyma populi NRRL Y-12728

Authors: Saha, Badal; Kennedy, Gregory - Greg

Submitted to: Preparative Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2020
Publication Date: 12/11/2020
Citation: Saha, B.C., Kennedy, G.J. 2020. Optimization of xylitol production from xylose by a novel arabitol limited co-producing Barnettozyma populi NRRL Y-12728. Preparative Biochemistry and Biotechnology. https://doi.org/10.1080/10826068.2020.1855443.
DOI: https://doi.org/10.1080/10826068.2020.1855443

Interpretive Summary: Developing new markets for use of corn stover and wheat straw will require new ways to convert these residues to value-added products. Xylitol is a promising solution. It is a natural food sweetener with proven health benefits to ward off dental decay and help diabetics. The annual market for xylitol is nearly one billion dollars. It is manufactured using xylose, which is a sugar that is abundant in these residues. ARS researchers have developed efficient processes for producing xylitol using yeast fermentations. However, yeast also produce arabitol as a contaminant from these residues. This is a showstopper because it is very expensive to remove arabitol. This problem has been solved by screening 99 yeast and finding one that produced arabitol-free xylitol from corn stover derived sugars. In this work, the fermentation was successfully optimized to lower the needed nutrients for growing the yeast all while producing more xylitol faster. The results are encouraging enough to warrant developing bioprocess technology for production of arabitol-free xylitol from biomass. The work should be of interest to National Corn, Wheat and Sorghum Growers.

Technical Abstract: Xylitol is a widely marketed sweetener with good functionality and health promoting properties. Xylitol can be synthetized by many yeast species in a one-step reduction of xylose. Arabinose is a common contaminant found in xylose and there is ongoing interest in finding biocatalysts that selectively product xyltiol. From a successful targeted screen of 99 yeasts, Barnettozyma populi Y-12728 was found to selectively produce xylitol from both mixed sugars and corn stover hemicellulosic hydrolysate. Here, fermentation conditions for xylitol production by B. populi were optimized. The medium for xylitol production was optimized through response surface methodology. The yeast produced 31.2 ± 0.4 g xylitol from 50 g xylose per L in 62 h using the optimized medium. The optimal pH for xylitol production was 6.0. Glucose (10 g L-1) was a strong inhibitor of xylitol production (54% inhibition in 72 h). Acetic acid (6.0 g L-1), HMF (4 mM) and ethanol (2.0 g L-1) inhibited the xylitol production by 18, 8, 57%, respectively, in 72 h fermentations. The glucose inhibition was entirely mitigated by using a 2- stage aeration strategy, indicating that the yeast was inhibited by the ethanol produced from glucose under low aeration. This culture strategy will greatly benefit xylitol production from hemicellulosic hydrolysates, which often contain glucose. This is the first report on the optimization of xylitol production by a Barnettozyma species.