Abstract: The physicochemical properties of fish skin gelatin prepared by sequential microwave and rapid freezing-thawing pretreatment coupled to gelatinization were characterized by measurement of isoelectric point, transmittance, gel strength, rheological properties and amino acid composition as well as using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared (FTIR) spectroscopy. Different from commercial type A and type B gelatins, the gelatin prepared in this study had an isoelectric point of 7. The transmittance was 57.13% and 78.07% at 450 and 620 nm, respectively, and the gel strength was 524.40 Bloom g, meeting the requirements of the Chinese national standard (transmittance at 450 nm ≥30%, transmittance at 620 nm ≥50%, and gel strength ≥ 50 Bloom g). Compared with that prepared by the traditional acid method, the gelatin had more hydrogen bonds as well as a complete triple helix structure and the proportion of sub-amino acids was similar between both gelatins. However, due to the small proportion of polymer subunits, gel properties were generally inferior to those of the traditional gelatin. In general, the method presented in this study is suitable for the green and clean preparation of gelatin.

Key words: gelatin; microwave; freezing-thawing; physicochemical properties