Effects of agitation rate and dissolved oxygen on xylose reductase activity during xylitol production at bioreactor scale

Katherine Manjarres-Pinzón,Dary Mendoza-Meza,Guillermo Correa-Londoño,Eduardo Rodriguez-Sandoval,Mario Arias-Zabala

doi:10.1590/fst.04221

Katherine Manjarres-Pinzón, Dary Mendoza-Meza + Show 3 more

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https://doi.org/10.1590/fst.04221

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Abstract

The study of xylose reductase (XR) - one of the key enzymes in the production of xylitol - is important in the fermentation process to have maximum efficiency in the bioconversion of xylose to xylitol in lignocellulosic hydrolysate. The aim was to evaluate the effect of agitation rate and dissolved oxygen at 7 L bioreactor scale on the production of xylose reductase (XR) from Candida tropicalis during the bioconversion of xylose into xylitol in the non-detoxified oil palm empty fruit bunch (OPEFB) hydrolysate. The highest xylose consumption (95.5%) and the maximum xylitol production (5.46 g.L-1) were presented under 30% dissolved oxygen and 50 rpm. The maximum XR activity (0.646 U mg-1 protein) was obtained after 144 h of fermentation and at the same conditions of dissolved oxygen and agitation rate mentioned above. The oxygen availability influences the XR activity of C. tropicalis and the xylitol production, observing a xylitol yield factor (YP/S) of 0.27 g.g-1 and volumetric productivity (QP) of 0.33 g.L-1 h-1. At lower dissolved oxygen regardless of the agitation conditions evaluated, an increase in xylitol production was evidenced.

Highlights

Hemicellulose, the second most abundant polysaccharide in nature, is used to generate value-added products such as xylitol; a penta-hydric alcohol of xylose widely used in the food industry as well as in products for oral care, pharmaceuticals and cosmetics (Arruda et al, 2011)
The bioconversion from xylose - contained in non-detoxified oil palm empty fruit bunch (OPEFB) hydrolysate - to xylitol by C. tropicalis was evaluated under various oxygen and agitation conditions in a 7L bioreactor (Figure 1a)
Xylose is consumed to a greater extent under conditions of 30% DO and 50 rpm showing a consumption of 95.5%, whereas conditions of 80% DO and the same agitation rate showed a xylose consumption of only 69%

Summary

Introduction

Hemicellulose, the second most abundant polysaccharide in nature, is used to generate value-added products such as xylitol; a penta-hydric alcohol of xylose widely used in the food industry as well as in products for oral care, pharmaceuticals and cosmetics (Arruda et al, 2011). The xylitol yield and substrate consumption must be high and production costs low for the xylitol industrial application. Low cost xylitol production involves the use of a xylose source without the need for detoxification, yeast cell recycling, high yield of xylose to xylitol, high productivity, less energy input, easy post-processing to purify xylitol and use of fermentation media from industrial by-products (Yewale et al, 2017). One of the biotechnological trends for the xylitol production is the development of recombinant strains with high production potential of xylitol, such as Saccharomyces with Candida XYL1 gene, because the first species is more tolerant in terms of xylose fermentation, toxicity and growth tolerance in the presence of inhibitors of hemicellulosic hydrolysates (Prakasham et al, 2009). The strains used in this study have not had any genetic transformation and are native strains (Yokoyama et al, 1995)

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