For the second portion, the skins were pretreated with 0.05 mol/
L citric acid using skin/solution ratio of 1:10 (w/v) for 2 h to remove
phospholipids. After stirring and washing as previously described,
the skins treated with citric acid were defatted using 300 mL/L
isopropanol with a skin/solvent ratio of 1:10 (w/v) at room temperature
for 1 h. The mixture was stirred continuously at 200 rpm.
The solvent was then removed and the defatted skins were washed
with 10 volumes of tap water. The defatted skins were then rinsed
with distilled water. The obtained skins were referred to as
‘defatted skins’.