Chondroitin sulphate (ChS) from the scapular cartilage of the shortfin mako shark (Isurus oxyrinchus) was purified by two-stage enzymatic hydrolysis and a fractional precipitation process using isopropyl alcohol. Characteristics of the ChS fraction were investigated using cellulose acetate membrane electrophoresis and FT-IR spectra. A maximum hydrolysis rate of 78.26% was achieved with 1.35% (w ⁄ w) Alcalase and 1.20% (w ⁄ w) Flavourzyme. A minimum nitrogen content of 2.89% was obtained with 1.43% (w ⁄ w) Alcalase and 1.33% (w ⁄ w) Flavourzyme, as determined by response surface methodology. The precipitation of ChS from the enzymatic hydrolysates was optimised at 40% (v ⁄ v) isopropyl alcohol, which contained 2% (w ⁄ v) NaCl to lower the nitrogen content. The precipitate was further purified via membrane filtration (molecular-weight cut-off, 3 kDa) to remove salt and low-molecular-weight materials. The ChS purified by enzymatic hydrolysis, isopropyl alcohol precipitation and membrane filtration was identified as ChS C by electrophoresis and FT-IR spectra.
Gelatin from yellowfin tuna (Thunnus albacares) dorsal skin was optimized for adhesive strength to plywood using surface response methodology of a central composite design with a dependent variable of adhesive strength (Y, kg f /cm 2 ) and two independent variables of gelatin concentration (X 1 , %) and hardening time (X 2 , hrs). From the above design, a maximum adhesive strength of 49.84 kg f /cm 2 was obtained under the optimal treatment condition of 15.85% gelatin concentration and 25.68 hr hardening time. The adhesive strength under optimum conditions was 50.93 kg f /cm 2 . The adhesive strength of the tuna gelatin was shown to be superior to that of bovine and porcine gelatins which had adhesive strengths of 34.75 and 34.9 kg f /cm 2 , respectively.
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