Collagen is the most abundant insoluble protein found in the extracellular matrix and connective tissue (skin, tendon, bone, cartilage, muscle, ligament, etc.) and accounts for about 30% of the body protein content. There are more than 20 different collagens, but I, II and III collagens account for more than 80% in mammals and consist of a triple helix structure consisting of three Pro-Collagen strands with Gly-Pro-Hyp sequences. Total Collagen assay kits based on the detection of hydroxyproline. Hydroxyproline hydrolyzed from collagen is oxidized to form a reaction intermediate and is sensitive and easy to measure at absorbance (560 nm).