木聚糖(xylan)是一種存在于植物細胞壁中的異質多糖，約占植物細胞干重的15%~35%，是植物半纖維素(hemicellose)的主要成分。大多數木聚糖是一種結構復雜的、具有高度分枝的異質多糖，含有許多不同的取代基。木聚糖的生物降解也因此需要一個復雜的酶系統，通過其中各種組分的相互協同作用來降解木聚糖。因此，木聚糖酶是一組酶，而非一種酶。

Xylan (Xylan) is a kind of heterogenous polysaccharide which exists in the plant cell wall. It accounts for about 15% ~ 35% of the dry weight of plant cells and is the main component of hemicellose. Most xylans are complex, highly branched, heterogeneous polysaccharides with many different substituents. Therefore, the biodegradation of Xylan requires a complex enzyme system, through which the interaction of various components to degrade xylan. Therefore, xylanase is a group of enzymes, not an enzyme.