*2.7. Xylitol Fermentation*

Xylitol fermentation experiments were performed using *Candida boidinii* NCAIM Y.01540 in shake flasks. Xylitol fermentation on a semi-defined xylose medium was carried out in 100 mL-shake flasks containing 35, 50, or 65 mL medium (pH 6) at 30 ◦C in a rotary shaker (125 rpm) for 96 h. The semi-defined xylose medium contained 10 g/L yeast extract, 15 g/L KH2PO4, 1 g/L MgSO4.7H2O, 3 g/L (NH4)2HPO<sup>4</sup> and 30, 55, or 80 g/L xylose. Before inoculation, the solutions containing the xylose and other components were sterilized in an autoclave (121 ◦C, 20 min) separately to avoid the Maillard reaction. Initial cell concentrations were 5 g (dry cell mass)/L. The experiments were carried out according to designed experiments (Table 2). The experiments for model validation were carried out in duplicates.


**Table 2.** Results of xylitol fermentation during the designed experiments (3<sup>2</sup> ) by using *Candida boidinii* NCAIM Y.01308. (OTR: oxygen transfer rate, IXC: initial xylose concentration).

\* Equal to the maximum xylitol yield.

Xylitol fermentations on xylose-rich hydrolysates of wheat bran and rice straw (WB1/S, GRS/S, and GRS/S supplemented with ammonium-sulphate; GRS/S supplemented with peptone, and GRS/S clarified by activated carbon and supplemented with peptone) were performed in 100-mL shake flasks filled with 50 mL hydrolysates at 30 ◦C in a rotary shaker (125 rpm) for 96 h. The initial cell concentrations were 5 g (dry cell mass)/L.

All the fermentations were monitored by taking and analyzing samples every 24 h. The samples were analyzed by spectrophotometer for optical density and high-performance liquid chromatography (HPLC) for sugars, alcohols and organic acids.
