Rheological properties of the swim bladder colloid from Atlantic cod (Gadus Morhua) and its digestive characteristics

The swim bladder colloid (SWG) was prepared by the swim bladder (SW) from Atlantic cod (Gadus Morhua), and its physicochemical, rheological and digestive properties were evaluated. It showed SW mainly consisted of collagens and chondroitin sulfate. The optimal condition of SWG was treated with acetic acid for 4.0 h, operated with high temperature and pressure time for 30 min and homogenized twice at 100 MPa pressure. The viscosity of SWG, containing the mixed system of proteins and polysaccharides, decreased with the increasing of shear rate, exhibiting shear thinning behavior, which conformed to pseudoplastic fluid. It demonstrated larger values for G'' than that for G' at the frequency of 20 Hz at 25 °C, which reached 30.8 Pa and 5.15 Pa at 60% concentration, respectively. Moreover, when the concentrations increased from 20% to 80%, the gelation temperatures and the melting temperatures increased from 6.79 ± 0.01 °C and 12.61 ± 0.06 °C to 13.73 ± 0.06 °C and 18.31 ± 0.05 °C, respectively. All of G''/G' were much less than 0.1, confirming the presence of solid-like elastic behavior at 4 °C. When the temperature increased from 40 °C to 85 °C, the viscosity at 20% concentration of SWG decreased from 34.50 mPa·s to 8.07 mPa·s at the shear rate of 100 s-1. Furthermore, it exhibited that SWG was digested and degraded after simulated digestion in vitro, and bioactive peptides were produced.