*2.5. Analytical Procedures*

The chemical composition of HS, AS, and solids from delignification were analyzed using the following TAPPI standard methods: moisture: T-264-cm-97, ash: T-211-om-02, structural carbohydrates, and Klason lignin: T-249-cm-85 [31–33]. The latter method is based on a two-step quantitative acid hydrolysis (QAH) performed with 72 and 4% H2SO4, respectively. The insoluble residue from QAH was oven-dried and weighed for Klason lignin determination. The liquid phase from QAH was assayed for glucose, xylose, arabinose, acetic acid, furfural, and hydroxymethylfurfural by HPLC, using a 1200 series instrument (Agilent Technologies, Santa Clara, CA, USA) fitted with a refractive index detector) and a 300 × 7.8 Aminex HPX-87H column (BioRad Life Science Group Hercules, CA, USA). The instrument detector was kept at 50 ◦C. The mobile phase was 0.003 N H2SO<sup>4</sup> eluted at 0.6 mL·min−<sup>1</sup> . The results allowed the determination of cellulose, xylan, arabinan, and acetyl groups present in the solid substrates. The acid-soluble lignin (ASL) was quantified spectrophotometrically at 205 nm. The total lignin was calculated as the sum of Klason lignin and ASL. All the analyses were performed in triplicate.

Aliquots from autohydrolysis and liquid phases from delignification assays were subjected to quantitative posthydrolysis (4% of H2SO<sup>4</sup> at 121 ◦C for 20 min), and the increase in the concentrations of monosaccharides and acetic acid caused by posthydrolysis measured the amounts oligomers and their degree of substitution with acetyl groups. All the analyses were performed in triplicate.
