Characterizations of Gelatin from the Skin of American Bullfrog (Rana catesbeiana) as Affected by Extraction Temperature

We investigated the effect of extraction temperature on the gel properties of gelatin from the skin of the American bullfrog (Rana catesbeiana) and the mechanisms. The textural and rheological properties of bullfrog gelatin extracted at 45 °C (G45), 55 °C (G55), and 65 °C (G65) were measured. The molecular weight distributions, microstructures, and amino acid compositions of the bullfrog gelatins were also determined. G45, G55, and G65 had gel strengths of 272.1, 225.6, and 205.8 g and hardness values of 28.1, 24.0, and 22.5 N, respectively. The gelling temperatures ranged from 19.3 to 23.9 °C, and the melting temperatures ranged from 28.9 to 31.5 °C. All the results were compared with those of commercial porcine gelatin. We propose that the higher gel strength of G45 with a higher band intensity of α2-chains compared with G55 and G65 was more likely to form ordered and strong cross-links. The gelatin extracted at a lower temperature (G45) had a finer gel structure, suggesting that it would be more difficult to disrupt by applied force. Gelatin extracted at a lower temperature demonstrated better properties with α2-chains and a fine gel structure. These results provide basic information on the extraction of American bullfrog skin gelatin for industrial applications.