Study On The Properties And Modification Of Gelatin From Skin Of Silver Carp(Hypophthalmichthys Molitrix) And Preparation And Properties Of Gelatin-based Edible Films

We extracted the fish skin gelatin and analyzed its physical and chemical properties and rheological properties in this paper. Then the tea polyphenols were used for the modification, to improve the gel strength and thermal stability. After that, the silver carp skin gelatin film and the complex films incorporated tea polyphenols and chitosan were prepared. The mechanical properties, barrier properties and biological activities were also measured. At last, trying to use the composite film on packaging the oil and fresh fish, to observe the influence on the quality of food. The main results were as follows: 1. The extraction and properties analysis of fish skin gelatinThe extraction yield of the silver carp skin gelatin was 58.33%, the fat content was 0.14%. The structure of the fish skin gelatin presents the status of random coil which is similar to the commercial gelatin. The α-chain content in the molecular organization of the fish skin gelatin was higher than the commercial gelatin high. The commercial gelatin had more imino acid. Also the content of hydrophobic amino acids in commercial gelatin was 32.54%, which is higher than that of fish skin gelatin was 31.73%. The phase-transition temperature was related to the thermostability, both of the commercial gelatin’s phase-transition temperature were all higher than the the silver carp skin gelatin’s, so the thermostability of the commercial gelatin was significantly stronger than the fish skin gelatin. 2. The modification effects on silver carp skin gelatin with tea polyphenolsThe infrared spectrum peak positions of silver carp skin gelatin with and without tea polyphenols showed the movement to the low wave number of the amide A, which revealed the hydrogen bond of the imino group and the hydroxyl group of tea polyphenols had been created. The SDS-PAGE patterns had no change because the hydrogen bond has been destroyed in the SDS solution. The gel strength of the silver carp skin gelatin was 460.65 g, then the gel strength of the silver carp skin gelatin with tea polyphenols rose to 584.90 g, however the gel strength with excessive tea polyphenols reduced to 430.02 g. The phase-transition temperatures were 31.10℃ and 20.80℃, they rose to 37.00℃ and 24.09℃, but the phase-transition temperatures reduced significantly with excessive tea polyphenols. 3. The preparations of edible composite filmsTo prepare film forming solutions, silver carp skin gelatin powder and chitosan was dissolved to achieve the final concentration of 3% and 3%, respectively. Glycerol was added at a level of 20%.The film forming solution pH was adjust to 5-6, then the gass was deaerated. In all formulations, solution was cast onto the acrylic plate, air-blown and dried.The thickness had no change with tea polyphenols, but became thicker with chitosan. The color was bright and changed to orange with tea polyphenols and chitosan. With the addition of tea polyphenols, the films had lower swelling ratios, lower WVPs, better mechanical properties and higher antioxidant activities. With the addition of chitosan, the films had significantly lower swelling ratios.The thickness of the edible composite films was 50.08μm. The films were acceptable in appearance as edible packaging film. The strength of extension of the films was 38 MPa, the elongation at break was about 30%. The composite film’s DPPH free radical-scavenging activity was high, and the ascorbic acid equivalent increased significantly. 4. The application of edible composite filmsThe film of silver carp skin gelatin had a high light transmittance and good mechanical properties which could satisfied the requirement of the preservation of oil and fresh fish. The rancidity did not differ significantly with the no packing controls. The driage in the process of fish storage was higher than the no packing controls because the composite films could absorb water. Tea polyphenols can retard the rancidity of oil and can significantly reduce the oxidation rate of oil. Tea polyphenols has certain antibacterial activity, it could obviously inhibit the putrefaction of fresh fish meat during the preservation. With the addition of chitosan, the films could preservatize the fresh fish well. The final composite film inhibited the corruption of fresh fish for 4 to 5 days.