Advances in xylooligosaccharides from grain byproducts: Extraction and prebiotic effects

Xylooligosaccharides (XOS) are mainly derived from lignocellulosic materials, such as rice husk, corn cobs, straw, wheat bran, wheat straw and other grain by-products. XOS have become one of the functional oligosaccharides of great concern at home and abroad due to their beneficial functional properties, such as low calorie, high stability, poor digestibility and high performance in proliferating probiotics. At present, the XOS extraction methods from grain byproducts mainly include autohydrolysis, acidolysis and enzymolysis. Among them, autohydrolysis has high requirements for equipment for achieving higher extraction rate and higher purity of products; and acidolysis can cause environmental pollution due to the usage of harmful reagents. Enzymolysis is the most common method for the production of XOS because of its high convenience, high efficiency and no pollution; and the widely used enzyme is the xylanase from Aspergillus niger. Current researches have showed that XOS can be utilized by probiotics such as Bifidobacteria and Lactobacillus to exert prebiotic effects, such as optimizing intestinal flora, promoting intestinal health, improving intestinal barrier, enhancing immune function, improving antioxidant capacity and so on. However, XOS extracted from the grain by-products contain a large amount of impurities, which limits their industrial application and makes it difficult to control the product quality. Therefore, XOS refining, separation and purification has become the key to their subsequent industrial application. This paper reviewed the current status of XOS extraction technologies from various grain by-products, and also summarized the prebiotic effect of XOS to provide reference for industrial production of XOS and its wide application in prebiotics market, thereby facilitating utilization and development of grain byproducts.