Extraction of pepsin-soluble collagen (PSC)
The undissolved residue obtained after ASC extraction was used
for further extraction with the gastric proteinase pepsin. The residue
was soaked in 0.5M acetic acid with a solid/solvent ratio of 1:15
(w/v) and pepsin (20 U/g residues) added. The mixture was
continuously stirred at 4°C for 3 days, followed by filtration through
two layers of cheesecloth. The filtrate was subjected to precipitation
and the pellet dialyzed, as previously described for ASC. The
dialysate was freeze-dried and is referred to as pepsin-soluble
collagen (PSC). The yield of PSC was calculated in the same manner as ASC. Additionally, the accumulated yield of collagen
was calculated from the total yield of ASC and PSC.