Quality of gelatin extracted from skin of Dominant Ray fishes of the Persian Gulf

Rays have high stocks in the Persian Gulf and Oman Sea, and are caught as by-catch in different fishing gears. Yield and Quality of gelatin extracted from the skin of dominant ray species of Persian Gulf, included: Butterfly ray (Gymnura poecilura), Sting ray (Himantura gerrardi), Honeycomb Sting ray (Himantura uamak) and Eagle ray (Aetomylaeus maculatus), were studied. Biometric results and the mean of skinning yield for each species were reported. Skinning yield for Eagle ray was 3. 2% that was significantly lower than other species (with > 60%). Gelatin extraction was done in constant conditions by Chloridric acid pretreatment. The results of qualitative identification of samples were positive and according to standards, concluded that the extracted products were gelatin. Also, total nitrogen, humidity and pH of samples were in standard limits, but ash content was upper than maximum standard level. Minimum concentration of extracted gelatins for gel formation were and no significant differences were observed between extracted gelatin samples. Melting temperature of rays gelatins ranged 20-25 C. Maximum and minimum yield of gelatin extraction yield were 20. 4% and 19. 0%, respectively. No significant difference were observed between gelatin extraction yield of four ray species (P >0. 05). Results suggested that for industrial uses, the skin of different ray species can be mixed and use together.