Physicochemical and molecular properties of gelatin from skin of golden carp (Probarbus Jullieni) as influenced by acid pretreatment and prior-ultrasonication

Gelatins from golden carp skin pretreated using different acids (acetic acid and sulfuric acid + acetic acid), with and without prior-ultrasonication, extracted at 55 °C for 3 and 6 h, were characterized. Different extraction efficiency and gelatin properties were obtained with different acid pretreatments. Prior-ultrasonication (20 kHz) with amplitude of 80% increased the yield of gelatins from acetic acid and sulfuric acid + acetic acid pretreated skins by 110.9% and 174.8%, respectively, compared with the corresponding controls (without prior-ultrasonication), when extracted for 6 h. All the gelatin samples had α- and β-chain as the major components. The gelatins extracted from skin with prior-ultrasonication showed slightly higher content of imino acids, compared to those produced by conventional method, regardless of acid pretreatments. Moreover, gelatin extracted by prior-ultrasonication had higher gelling and melting temperature than those produced by conventional method by 9.1–12.0 and 8.2–12.2%, respectively. FTIR spectra revealed that the formers had the higher cross-links stabilized by hydrogen bond than the latter. Based on microstructure study, the formers had higher number of interjunction zones with finer networks. Overall, pretreatment with sulfuric acid/acetic acid in combination with prior-ultrasonication effectively improved the extraction efficiency and gelling properties of gelatin from golden carp skin.