Screenning on Xylitol Production with Different Colombian Native Yeasts

 

Corresponding autor: jntorresl@unal.edu.co

Jessica Torres-Leiva^a, Sebastián Lancheros-Castañeda^a, Yina Cifuentes-Triana^a, Daniel Leal-Moreno^a, Juan Pablo Ortíz-Rosas^a, Mario Velásquez-Lozano^a

^a Universidad Nacional de Colombia - Bogotá, Department of Chemical and Environmental Engineering, Avenida Carrera 30 No. 45 - 03, 111321, Bogotá, Colombia.

Recently, bioconversion of biomass residual feedstocks has received particular attention because of its practical applications in various agro-industrial processes, as fuels and add-value chemicals production, energy generation and effluent remediation. Different agricultural residues, such as corn fiber, corn stover, wheat straw, rice straw and sugarcane bagasse, contain about 20 â?? 40% hemicellulose, the second most abundant polysaccharide in nature.

Hemicelluloses are heterogeneous polymers of pentoses (xylose, arabinose), hexoses and sugar acids. D-xylose is the principal sugar constituent of hemicelluloses and it can be reduced to different products as ethanol, xylitol, 2-3 butanediol and lactic acid through bioprocessing with microbial strains. Specifically, xylitol production has attracted much attention due to its potential use as natural food sweetener and sugar substitute for diabetics with anticarcinogenic properties. Xylitol bioconversion is limited to strains with the ability to metabolize xylose as carbon source.

Xylose assimilation ability was screened in eighty-five wild yeasts isolated from a Colombian distillery in a solid media with xylose as sole carbon source. Forty strains were able to growth in Yeast Medium Agar containing 20 g/L glucose, 20 g/L peptone, 10 g/L yeast extract and 20 g/L agar-agar at 48 hours. Xylitol production was evaluated on the xylose-assimilating strains under oxygen-limited conditions, 150 rpm. 30°C, and a media containing 30 g/L xylose, 1.7 g/L yeast nitrogen base (YNB, Sigma Aldrich®) and 5 g/L (NH₄)₂SO₄. Most of the strains were able to metabolize xylitol in 96h. Six strains of different species presentend the higher concentrations of xylitol: Candida tropicalis, Issatchenkia orientalis, Meyerozyma caribbica and Torulaspora delbruekii and two strains with no identity determined. 

The best results were gained with Candida Tropicalis; a 4 g/L concentration of xylitol was obtained at 96 hours in 125 mL flasks with 50 mL of fermentation media. This strains fo were obtained from a Colombian distillery, particularly from bagasse in the floor near to a boiler, which suggests that Candida Tropicalis may be able to grow in a hydrolysate of sugarcane bagasse.