A biorefinery strategy for the manufacture and characterization of oligosaccharides and antioxidants from poplar hemicelluloses

Abstract

A combination of biorefinery processes (hydrothermal and membrane processing) was performed for the manufacture of oligosaccharides and natural phenolic compounds from poplar hemicelluloses. Both, oligosaccharides and phenolics have multiple potential applications related to their bioactive properties. Firstly, non-isothermal autohydrolysis of poplar was performed to obtain oligosaccharides from the hemicellulosic fraction, while cellulose and lignin remained almost unaltered in the spent solid allowing their valorization in further processing stages. Operating at 210 o C and liquid to solid ratio of 6 kg/kg, solutions containing 28.71 g oligosaccharides/L were obtained. Secondly, membrane refining of the resulting solution and further freeze-drying resulted in a product with high purity (90 kg of substituted oligosaccharides/100 kg of non-volatile compounds). The yield of substituted oligosaccharides in the target product accounted 16.6 kg/100 kg of poplar wood. Product characterization was accomplished by HPLC, HPSEC, HPAEC-PAD and MALDI TOF-MS. The data confirmed the presence of backbones containing up to DP13 pentose units, with a complex substitution pattern by acetyl groups and O-methyl-uronic moieties. Additionally, the presence of natural phenolic compounds bounded to oligosaccharides conferred antioxidant properties to the target product. Substituted oligosaccharides and phenolics are postulated as valuable products with interest in food and pharmaceutical industries.