The calcium-binding activity of fish scale protein hydrolysates

The calcium-binding activity of tilapia scale protein hydrolysates sequentially hydrolyzed by trypsin, flavor enzyme and pepsin were investigated. The hydrolysates were divided into four fractions using G-15 gel chromatography, and the F3 fraction has the higher calcium-binding activity of 196.3 mg/g. The UV-vis and the Fourier transform infrared spectroscopy (FTIR) demonstrate that the amino nitrogen atoms and the oxygen atoms belonging to the carboxylate groups are the primary binding sites for Ca2+. The X-ray diffraction and scanning electron microscopy (SEM) confirmed the reaction between the peptde and calcium. The results obtained indicated that this fish scale protein hydroly-sates have potential as functional foods for calcium-supplementation.

Effects of protein oxidation, cathepsins, and various freezing temperatures on the quality of superchilled sturgeon fillets

Many aquatic products have been stored using superchilling technology, but rarely used for the storage of sturgeon fillets. In this study, we investigated the effects of protein oxidation, cathepsin, and various freezing temperatures on the quality of superchilled sturgeon fillets. Sensory evaluation results showed that the sensory attributes of superchilled (−3 °C) sturgeon fillets were acceptable three times longer (18 days) than samples stored at refrigeration temperatures (4 °C). The sarcoplasmic protein, carbonyl, myofibrillar protein, total sulfhydryl content and the surface hydrophobicity were determined using fluorescence spectrophotometry and SDS-PAGE. Results showed that superchilling might protect myofibrillar proteins from oxidation compared to refrigeration temperatures. The activity of the three cathepsins (B, L, and H) in terms of myofibrillar, mitochondria, lysosomes, and sarcoplasm demonstrated that superchilling can inhibit cathepsins activity in sturgeon and protect its muscle structure. Microscopic observations showed that as the temperature decreased, the gap area of the muscle fibers decreased, and the deformation of cross-sectional slices was gradually reduced. In addition, the freezing rate of ice crystals produced during the freezing process influenced the muscle structure, texture, and sensory attributes. Superchilled sturgeon fillets showed good hardness, chewiness, and water retention. In conclusion, superchilling technology shows promise for its ability to extend the shelf life while maintaining the texture and sensory attributes of fresh sturgeon fillets.