Xylan is a polysaccharide belonging to the family of hemicelluloses, which make up the cell wall of plants. Xylan is present in dietary fibres and corresponds to a carbohydrate polymer of xylose.
It is broken down by enzymes called xylanases. These enzymes belong to the family of glycoside hydrolases. They need water molecules to function.
The xylanase degrades xylan and causes the release of xylose : a five-carbon ose (monosaccharide).
Like all mammals, man is not capable of synthesising xylanases, unlike bacteria, fungi, snails or insects, which possess the genes coding for xylanases.