L-Arabinose (CAS: 5328-37-0) belongs to the class of compounds known as aldopentoses. An aldopentose is a monosaccharide containing five carbon atoms, including an aldehyde (CHO) functional group. Arabinose gets its name from gum arabic, from which it was first isolate. Most saccharides found in nature are in the "D"-form, however, L-arabinose is in fact more common than D-arabinose. L-arabinose is found in nature as a component of biopolymers such as hemicellulose and pectin. L-arabinose is found in all organisms from bacteria to plants to animals. Arabinose is the second most abundant pentose in lignocellulosic biomass after xylose. There are two different arabinose utilization pathways in nature: bacterial and fungal. The bacterial pathway converts arabinose into xylulose-5-P via ribulose-5-P using three enzymes (L-arabinose isomerase, L-ribulokinase, and L-ribulose-5-P 4-epimerase) after which it enters the pentose phosphate pathway for ethanol production. The fungal pathway converts arabinose into L-arabinitol by aldose reductase (AR) or XR, L-xylulose by L-arabinitol 4-dehydrogenase (LAD), xylitol by L-xylulose reductase (LXR), D-xylulose by xylulose dehydrogenase (XDH), and D-xylulose-5-P by xylulose kinase (XK), and lastly enters the nonoxidative pentose phosphate pathway for further metabolism.  Arabinose has a sweet taste and is one of the most abundant components released by complete hydrolysis of non-starch polysaccharides (NSP) of vegetable origin. Although widely present in nature, L-arabinose is rarely used in food production or food flavoring, and its physiological effects in vivo have received little attention. L-arabinose is known to selectively inhibit intestinal sucrase activity in a non-competitive manner. Sucrase is the enzyme that breaks down sucrose into glucose and fructose in the small intestine. As a result, L-arabinose suppresses plasma glucose increase due to sucrose ingestion. The presence of arabinose in urine may indicate overgrowth of intestinal yeast such as Candida albicans or other yeast/fungus species. L-arabinose is also a microbial metabolite found in, and produced by, Mycobacterium (PMID: 16232643). In a rare case of two autistic brothers that were not associated with any known metabolic disease, it was found the median value for L-arabinose in their urine samples was 179 umol/mmol creatinine, nearly six times greater than normal children (PMID: 11238761, 8931641, 1390604, 7628083).