Characteristics and functional properties of gelatin from thornback ray skin obtained by pepsin-aided process in comparison with commercial halal bovine gelatin

Abstract Potential utilization of skin by-product from thornback ray ( Raja clavata ) was investigated. Gelatin from alkali-pretreated skin was extracted without or with pepsin at pH 2.0 in 0.2 M acetic acid or 0.1 M glycine-HCl buffer. The addition of pepsin increased the yields of gelatin. Indeed, the yields of gelatin from thornbach ray obtained with pepsin treatment was about 30%, while those obtained in acetic acid or glycine-HCl buffer were 18.32% and 23.01%, respectively. The characteristics and functional properties of thornback ray gelatin (TRGP), obtained by treatment with 5 units of pepsin/g of skin in glycine-HCl buffer, were investigated and compared with halal bovine gelatin (HBG). TRGP had high protein content (90 g/100 g) similar to halal bovine gelatin (HBG). TRGP had a molecular weight (170 kDa) lower than HBG (226 kDa) and imino-acids content lower than HBG (10 and 22 residues per 100 residues, respectively). Its gel strength (140 g) was lower than that of HBG (260 g), possibly due to lower hydroxyproline content. Textural properties showed that the values hardness, elasticity, cohesiveness and chewiness of TRGP were lower than those of HBG. The functional properties of TRGP were examined in comparison to HBG. TRGP showed stronger ability to clarify apple juice than bovine gelatin. The nutritional component of clarified apple juice was practically not changed. As expected, the different origin and extraction process of HBG and TRGP influenced the properties of the corresponding gelatin solutions.