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The aim of this study was to evaluate the effect of different process conditions, such as the sulfuric acid concentration, contact time, solid:liquid ratio and particle size, on the xylose recovery and the formation of by-products from oil palm empty fruit bunch (OPEFB) with dilute-acid hydrolysis. Moreover, an adapted and non-adapted strain of the yeast Candida guilliermondii was used to obtain xylitol from the optimal hydrolysate. Xylose, glucose, hydroxymethylfurfural (HMF) and acetic acid in the acid hydrolysate were analyzed with high performance liquid chromatography (HPLC). A BoxBehnken-based design was used to find the combination of factors that maximized the formation of xylose in the hydrolysate optimization process. The fermentation to obtain xylitol from the optimized hydrolysate of OPEFB with adapted and non-adapted C. guilliermondii strains was made in 100 ml Erlenmeyer flasks at 30°C for 96 h at 200 rpm in an incubator shaker. The maximum xylose concentration (32.59 g L -1) was obtained at 121°C, for 30 min, with a 1:8 solid:liquid ratio, 2% acid concentration and particle size of around 4 cm. With the same conditions, the inhibitor concentrations, such as HMF, glucose and acetic acid, were 0.023, 1.033 and 11.078 g L -1, respectively. The optimized conditions were the same as previously described. The higher xylitol productivity (10.3 g L -1) and yield (0.43 g g -1) were obtained by fermentation with non-adapted C. guilliermondii strains from the optimized hydrolysate of OPEFB without the need for detoxification. It is not necessary to make an adaptation of C. guilliermondii in the optimized hydrolysate of OPEFB to produce xylitol.

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