- Xylose is a naturally occurring five-carbon sugar (monosaccharide) that belongs to the group of aldopentoses. Its molecular formula is C₅H₁₀O₅, and it is structurally characterized by the presence of an aldehyde group at the first carbon.
- It was first discovered in wood, which is reflected in its name derived from the Greek word xylon (wood). Xylose is widely distributed in nature and is considered one of the most abundant monosaccharides, second only to glucose. It primarily occurs as a building block of hemicelluloses, particularly xylans, which are important structural polysaccharides in the cell walls of hardwoods, grasses, and agricultural residues.
- In plants, xylose units are linked together in β-(1→4) glycosidic bonds to form the backbone of xylan. These polymers often carry side chains such as arabinose, glucuronic acid, or acetyl groups, giving them structural complexity and functional diversity. The abundance of xylans makes xylose a major component of lignocellulosic biomass, which is a key raw material for renewable energy and bio-based industries. During the hydrolysis of hemicellulose, free xylose can be released and subsequently fermented or chemically converted into value-added products.
- From a biological perspective, xylose is metabolized differently from hexoses like glucose. Many microorganisms lack efficient pathways for xylose utilization, but certain bacteria and fungi have evolved the ability to ferment xylose through the pentose phosphate pathway or via conversion into xylulose. In humans, xylose is only partially absorbed in the small intestine and is mostly excreted unchanged in the urine, which has led to its use in the D-xylose absorption test, a diagnostic tool for evaluating intestinal malabsorption.
- Xylose and its derivatives have significant industrial and commercial importance. It serves as a precursor for xylitol, a widely used low-calorie sweetener with dental health benefits and applications in diabetic-friendly foods. Xylose is also a promising feedstock for producing bioethanol, biodegradable plastics, and specialty chemicals, making it central to the emerging bioeconomy. Additionally, it has roles in pharmaceuticals, where its derivatives are investigated for prebiotic, antioxidant, and antimicrobial properties.
