Xylooligosaccharides: Transforming the lignocellulosic biomasses into valuable 5-carbon sugar prebiotics

Xylooligosaccharides (XOS) are prebiotics derived from lignocellulosic materials presenting important functional properties. Traditional methods of XOS production often require the presence of acidic and basic catalysts for xylan extraction. However, new strategies and technologies such as hydrothermal, steam explosion, and green catalysts have been used to obtain XOS. Overall, these technologies are considered more environmentally friendly due to the lower amount of waste generated. This review summarizes the strategies used in XOS production, describing the process variables involved in xylan extraction and depolymerization, mainly for the most cited biomasses: sugarcane bagasse, corncob and wheat straw. Additionally, technical applications in the food area and future perspectives are presented. The use of hydrothermal pretreatment may be a promising strategy for xylan extraction. Besides the higher pressure and temperature, the conditions can be optimized to achieve satisfactory yields with minimal release of impurities and inhibitors. The enzymatic treatment should be combined to achieve higher yields of XOS with a low degree of polymerization, which is required for prebiotic function. Importantly, adequate knowledge of the lignocellulosic composition of biomass, particularly, the characteristics of hemicellulose chains, is needed to determine the best process conditions.