Non-dissolved residue obtained after acid extraction was used for pepsin soluble collagen extraction. The residue was soaked in 0.5 Macetic acid with a solid to solvent ratio of 1:15 (w/v) and porcine pepsin (20 unit/g of residue) was added. The mixtures were continuously stirred at 4 C for 48 h, followed by filtration with two layers of cheesecloth. The filtrate was collected and subjected to precipitation and dialysis in the same manner with that used for ASC as previously described. The obtained collagen was referred to as ‘‘pepsin soluble collagen, PSC”.