Xylose

Xylose is a naturally occurring monosaccharide of the aldopentose class with the molecular formula C5H10O5. It exists in two enantiomeric forms, D-xylose and L-xylose, with D-xylose being the form most commonly found in nature, particularly in plant hemicelluloses such as xylan.

Chemically, xylose is a pentose sugar. As with other aldoses, it can exist in a linear form and in cyclic hemiacetal forms; in solution it predominantly forms furanose rings and exists as alpha and beta anomers. Its structure allows it to participate in standard sugar reactions, including oxidation to xylonic acids and reduction to sugar alcohols such as xylitol.

Xylose occurs in a wide range of plant materials, with large amounts found in hardwoods and agricultural residues. Commercially, it is obtained by hydrolysis of xylan-containing materials, followed by purification. It can also be produced enzymatically from xylan by xylanolytic enzymes. In industry, xylose serves as a precursor for various chemical derivatives and, upon hydrogenation, yields xylitol, a commercial sugar alcohol. Some xylose is fermented by certain yeasts and bacteria to ethanol or other products.

In humans, xylose is absorbed from the gastrointestinal tract and is partially metabolized via the pentose phosphate pathway to xylulose-5-phosphate. It is used in diagnostic D-xylose absorption tests to help distinguish causes of malabsorption. Xylose has a relatively low glycemic impact compared with glucose, but excessive intake can cause gastrointestinal discomfort and laxative effects.