Abstract
Xylitol is a sugar alcohol with five carbons that can be used in the pharmaceutical and food industries. It is industrially produced by chemical route; however, a more economical and environmentally friendly production process is of interest. In this context, this study aimed to select wild yeasts able to produce xylitol and compare their performance in sugarcane bagasse hydrolysate. For this, 960 yeast strains, isolated from soil, wood, and insects have been prospected and selected for the ability to grow on defined medium containing xylose as the sole carbon source. A total of 42 yeasts was selected and their profile of sugar consumption and metabolite production were analyzed in microscale fermentation. The six best xylose-consuming strains were molecularly identified as Meyerozyma spp. The fermentative kinetics comparisons on defined medium and on sugarcane bagasse hydrolysate showed physiological differences among these strains. Production yields vary from YP/S = 0.25 g/g to YP/S = 0.34 g/g in defined medium and from YP/S = 0.41 g/g to YP/S = 0.60 g/g in the hydrolysate. Then, the xylitol production performance of the best xylose-consuming strain obtained in the screening, which was named M. guilliermondii B12, was compared with the previously reported xylitol producing yeasts M. guilliermondii A3, Spathaspora sp. JA1, and Wickerhamomyces anomalus 740 in sugarcane bagasse hydrolysate under oxygen-limited conditions. All the yeasts were able to metabolize xylose, but W. anomalus 740 showed the highest xylitol production yield, reaching a maximum of 0.83 g xylitol/g of xylose in hydrolysate. The screening strategy allowed identification of a new M. guilliermondii strain that efficiently grows in xylose even in hydrolysate with a high content of acetic acid (~6 g/L). In addition, this study reports, for the first time, a high-efficient xylitol producing strain of W. anomalus, which achieved, to the best of our knowledge, one of the highest xylitol production yields in hydrolysate reported in the literature.
Highlights
Xylitol is a five-carbon polyol with different applications
JA1 to produce xylitol on hydrolysate was recently demonstrated [7]; Meyerozyma guilliermondii A3 was isolated by its fast growth on xylose and capability to produce xylitol on sugarcane bagasse hydrolysate [14]; and, Wickerhamomyces anomalus 740 isolated from a sugarcane mill sample by its ability to grow on sugarcane bagasse hydrolysate containing high concentration of acetic acid (8 g/L)
A screening strategy based on the ability to metabolize xylose was employed to select yeast strains to produce xylitol
Summary
Xylitol is a five-carbon polyol (sugar alcohol) with different applications. It possesses high sweetener potential, with a flavor similar to sucrose, and it can be used as a sweetener by patients with diabetes because it does not require insulin to be metabolized [1,2]. Xylitol leads to preventive action against inflammation of the airways, such as otitis, sinusitis and tooth decay since bacteria do not use it for growth [2,3] It has been pointed out as an interesting chemical product for worldwide applications in the chemical industry [4]. The biotechnological production of xylitol is attractive in a biorefinery context by the employment of environmental friendly processes to aggregate value to the xylose present in the hemicellulosic hydrolysates [3]. This process has the potential to offer lower costs for the production routes [6]
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