To remove non-collagenous proteins, the prepared fish skin was mixed with 0.1 MNaOH at a skin/alkali solution ratio of 1:10 (w/v). The mixture was continuously stirred for 6 h at 4 C and the alkali solution was changed every 2 h. The treated skin was then washed with cold water until a neutral or faintly basic pH of wash water was reached. The pH of wash water was determined using a digital pH meter (Sartorious North America, Edgewood, NY, USA).