Chitosan Oligosaccharide (COS)

Chitosan Oligosaccharide (COS) is a low-molecular-weight oligomer (typically 2–10 glucosamine units, MW ~1–10 kDa) derived from the enzymatic or chemical hydrolysis of chitosan, which itself is obtained by deacetylation of chitin. It is not a significant source of macronutrients (negligible fat, negligible digestible carbohydrate energy, and no complete protein). Key bioactive characteristics include: Primary bioactive compound: β-1,4-linked D-glucosamine oligomers with a degree of deacetylation (DD) typically ≥85–95%, conferring a polycationic character at physiological pH. Amino sugar content: Predominantly composed of D-glucosamine (2-amino-2-deoxy-D-glucose) residues, with minor residual N-acetyl-D-glucosamine units (~5–15% depending on DD). Glucosamine content per gram of COS is approximately 700–850 mg. Molecular weight range: Typical commercial COS preparations range from ~0.5 kDa (disaccharides) to ~10 kDa (decamers); lower MW fractions (1–3 kDa) generally exhibit superior water solubility (>99% soluble) and higher bioavailability compared to parent chitosan. Ash/minerals: Trace minerals may be present depending on source — calcium (1–3 mg/g), sodium (<5 mg/g), and trace amounts of magnesium and potassium from crustacean shell origin. Fiber classification: COS is classified as a soluble dietary fiber analog; however, it is largely non-caloric (~0 kcal/g metabolizable energy) as human digestive enzymes do not efficiently cleave the β-1,4-glycosidic bonds. Nitrogen content: Approximately 7–8% nitrogen by weight, attributable to free amino groups on glucosamine residues. Bioavailability notes: Unlike high-molecular-weight chitosan (which has poor solubility and <5% oral absorption), COS demonstrates high aqueous solubility across a broad pH range (pH 2–9) and significantly enhanced intestinal absorption — estimated oral bioavailability of 20–30% for oligomers ≤5 kDa, with smaller fragments (di- to pentamers) showing the highest absorption via paracellular and transcellular intestinal transport. COS is absorbed intact in the small intestine and can be detected in systemic circulation. No vitamins are inherently present. No significant lipid or protein content. The polycationic nature (pKa of amino groups ~6.3–6.5) is central to its fat-binding capacity (estimated ~3–5 g dietary fat bound per gram COS in vitro at gastric pH), its mucoadhesive properties, and its electrostatic interaction with bacterial cell membranes underlying antimicrobial activity.