*3.1. Autohydrolysis and Composition of HS and AS*

In previous studies reported by our research group, 210 ◦C was identified as the optimal autohydrolysis temperature for producing soluble hemicellulosic oligosaccharides [10]. Under the same conditions, soluble antioxidant compounds were extracted from the substrate [23]. Both oligosaccharides and antioxidant compounds find applications in a number of fields, including the food, cosmetic and pharmaceutical industries. Based on this information, HS autohydrolysis assays were performed at 210 ◦C, and the corresponding AS were selected for assessing the separation of cellulose from lignin.

Upon autohydrolysis, 35.4% of the dry HS mass was dissolved, yielding an aqueous phase with the following composition (in g/L): xylooligosaccharides, 16.15; glucooligosaccharides, 0.07; acetyl groups, 3.65; xylose, 1.02; arabinose, 0.31; acetic acid, 0.86; and total phenolic content, 1.60 g equivalent gallic acid/L. The average compositions of HS and AS are presented in Table 2. As expected, autohydrolysis causes the selective separation of hemicelluloses resulted in AS with increased percentages of cellulose (38.7%) and total lignin (50.4%).


**Table 2.** HS and AS composition, expressed as g of component/100 g of dry HS or AS, respectively. Data reported as average values ± standard deviations.
