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.