| Most films used to preserve foodstuffs are made from synthetic plastic materials. Recently, for the environmental reasons, attention has turned to biodegradable and edible films made from renewable seafood processing by-products. Fish gelatin, obtained form fish skin by products, is one of the environment-friendly materials. Because of its good biodegradability, fish gelatin has been a major focus of interest in packaging materials in the world. This paper aims to evaluate if transglutaminase (TGase) and chitosan with different molecular weights and degree of deacetylation can affect the rheology and mechanical properties of gelatin based films. The main contents of the research include the following several parts:(1) The properties of fish gelatin. Fish gelatin was from walleye pollock (Theragra chalcogramma) skin collagen, the content of imino acid (Pro+Hyp) was about 18.4 percent, which was much lower than the mammals gelatin. The results of SDS-PAGE showed that pollock skin gelatin was the typeⅠcollagen. The FTIR analysis revealed that the characteristic bands of collagen around 3299, 1658, 1544, and 1243cm-1 were correspond to amides A, amide-Ⅰ, amide-Ⅱand amide-Ⅲ, respectively .(2) The fish gelatin film-forming solution and its modification. The gel strength and rheological properties of fish gelatin solution were significantly improved after modification by transglutaminase or chitosan. The gel strength of the gelatin gel incorporated with 2% TGase (20mg of enzyme protein/mL) was about 227g, which was 127% higher than that of control film. After modification with chitosan, the gel strength was higher than that of control. The higher deacelation degree of chitosan the higher gel strength of the gelatin gel. However, there is no relationship between the gel strength and the molecular weights of chitosan. The gel strength of gelatin gel modification with 2% chitosan (DD=93.6%, M_w =550kDa) and 2% TGase was 182g, which was 82.0% higher than that of control. At 25℃, the storage modulus (G') and loss modulus (G'') of the modified gelatin gel was 20.2 and 7.40 times higher than those of control, respectively.(3) The properties of compound fish gelatin films. The mechanical property, water vapor permeability of fish gelatin films were improved after modificatio by TGase, chitosan, or chitosan combined with TGase. Compared with the gelatin film, the water vapor permeability (WVP) of the gelatin films modified with TGase and chitosan decreased 33.3%, and the thermal denaturation temperature increased 32.1℃(P<0.05). The tensile strength (TS) and elongation at break (EB) was 51.69MPa and 38.35% , increased by 2.78 and 2.09 times (P<0.05), respectively. The mechanical parameters of the film meet the needs of the national standard GB10457-2009.(4) The FTIR spectra, X-ray diffraction and micro structure of compound fish gelatin films. From the spectra, amide-Ⅰ, amide-Ⅱand amide-Ⅲpeaks of the gelatin-chitosan film shifted to lower wavenumbers, indicating These results indicated that the gelatin and chitosan were mixed well in the molecular level. With addition of chitosan and TGase, the gelatin underwent cross-linking via covalent and non-covalent bonding, resulting in greater intermolecular aggregation in the three-dimensional network.(5) The application of compound fish gelatin films. The compound films was used as coating package in shrimp preservation. The result indicated that the total bacteria and TVB-N of the shrimp were significantly reduced by the coating film treatment. The total bacteria and TVB-N of the shrimp treated by coating film were 32.1% and 48.9% lower than those of control at 6 days storage. In a word, shrimp treated by coating film had longer shelf-life and better quality than those of control during cold storage. |
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