The skins were soaked in 0.1 mol/L NaOH with a skin/alkaline
solution ratio of 1:10 (w/v) in order to remove non-collagenous
proteins. The mixture was stirred for 3 h at room temperature
(28e30 C) using an overhead stirrer model W20.n (IKA®-Werke
GmbH & CO.KG, Stanfen, Germany) at a speed of 300 rpm. The
alkaline solution was changed every 1 h for totally 3 times. Alkalitreated
skins werewashed with tap water until a neutral or slightly
basic pH (7.0e7.5) of wash water was obtained.