2.8.1. Concentration of Sugars, Alcohols, Organic Acids, Phenols, and Total Protein

Concentrations of glucose, xylose, arabinose, xylitol, ethanol, acetic acid, formic acid, furfural, and hydroxymethylfurfural (HMF) were determined by HPLC using BioRad (Hercules, CA, USA) Aminex HPX-87H (300 × 7.8 mm) column equipped with Micro-Guard Cation H+ Refill Cartridge (30 × 4.6 mm) pre-column at 65 ◦C, and a refractive index detector. The eluent was 5 mmol/L sulfuric acid at a flow rate of 0.5 mL/min. The injection volume was 40 µL. Due to the overlapping peaks of xylose and galactose, those sugars were determined as one component in the xylose-rich hydrolysates of wheat bran and rice straw. It was referred to as xylose throughout the text because of the low concentration of galactose expected in the hydrolysates [14,36]. The total phenol content was determined by the Folin-Ciocalteu (FC) reagent according to the method described by Guo et al. [37]. The total protein content of the hydrolysates was determined by the Bradford method [38].
