Chitin quantitation (as glucosamine) in food raw materials by spectrophotometry

Chitin is a water insoluble nitrogen-containing polysaccharide made from N-acetyl-D-glucosamine containing β-(1→4)-linkages. In food, chitin is considered as a source of fiber with prebiotic properties to gut microflora. Chitin content varies widely in nature from 1% (yeasts) up to 64% (butterfly cuticles) and is mostly found in filamentous or mushroom forming fungi, insects and crustaceans. This spectrophotometric method is suitable for chitin quantitation (reported as glucosamine) in food raw materials like insects (mealworm larvae, crickets), shrimps, mushrooms and fungi in a research (non-routine) laboratory. To remove interferences, the sample is defatted (Soxhlet) prior to acid hydrolysis in 6 M HCl. The color complex is developed after the addition of Katano's reagent (a mix of 0.05 mol/L sodium metasilicate, 0.6 mol/L sodium molybdate, 30% dimethyl sulfoxide and 1.42 mol/L acetic acid) at 70 °C for 30 min and measured at 750 nm against blank. A five-point linear calibration (5-100 µg/mL) is used. Limit of detection is 3 µg GLCN/mL. The correlation (R²) with an HPLC method for chitin analysis is at least 0.93.•a reliable alternative to an HPLC method•does not require expensive equipment•deproteination by alkali is not necessary for most matrices - saves about 30% of time.