| Tilapia(Oreochromis spp.) is one of the mostly bred fishes in the world. Quite a number of scales were produced during the process of products such as fillets. Most of the scales were discarded, however, not yet fully utilized. Scales are rich in protein and are considered as good raw materials of collagen and gelatin.In this thesis, scales of tilapia(Oreochromis spp.) were used for the extraction of scale gelatin. Conditions for gelatin extraction were optimized and characteristics of the gelatin were determined. In addition, gelatin extracted was modified by transglutaminase (TG) and properties of the modified products were studied. Eventually, TG modified gelatin was used as coating agent for tilapia fillets. And the effects of gelatin coating on the quality of fillets during storage were studied.The main contents and results in the study were as follows:The scales of tilapia were rich in protein, which were up to54.51%. The glycine, proline, glutamic acid and alanine were the most abundant in protein of tilapia scale, contents of which were12.3%,5.53%,5.27%and5.13%, respectively. When expressed as animo acid residues, the content of glycine was35.4%, approximately1/3of the total residues. Besides, glycine arranges at every third residue throughout most of collagen molecules, which was consistent with the character of Gly-X-X. The content of collagen of tilapia scale was30.32%on the wet weight, which account about56%of the crude protein.An Orthogonal experimental design L9(34) was applied to optimize the conditions of microwave-induced demineralization of the scale. The optimal treatment can be obtained to be decalcification time, microwave power and concentration of EDTA-Na2were60min,480W and0.15mol·L-1, respectively. The rate of decalcification was approximately52.2%under the conditions. Scanning electron microphotograph of the decalcified scale revealed that the treatment can effectively remove the minerals which cover the surface of the scale.Response surface methodology (RSM) with a4-factor,5-level central composite design was used to identify critical control factors for gelatin extraction from tilapia scales and characteristics of the gelatin were determined. The results suggested that the optimum extraction conditions were3.6h for extraction time,65℃for extraction temperature,11.3h for acid treatment time and20%(w/v) for citric acid concentration. The predicted value of yield was30.1%, while the experimental one was28.4%.Chemical compositions and properties of the scale gelatin were studied. Besides, bovine bone gelatin was used as control. The scale gelatin was characterized by high protein and low ash content. PH and pI values of the gelatin were5.0and8.7, respectively. The infrared spectrum of the gelatin was similar to that of pepsin-solubilized collagen from the scale. The denatuure temperature of the scale gelatin was28.1℃by viscometric method. The amount of imino acids (proline and hydroxyproline) was167and173residues per1000residues for the scale gelatin and bovine bone gelatin, respectively. The values of gel strength were271g and328g, respectively for the scale gelatin and bone gelatin. The degradation temperatures were about59.7℃and69.5℃for scale gelatin and the bone gelatin, respectively. As compared to the bone gelatin, the scale gelatin had visible β-component and degradation fragments, of which the molecular weight was less than100kDa.Extracted gelatins were enzymatic-cross-linking modified using transglutaminase (TG). The concentration of the gelatin solution to be modified was5%. The optimal conditions for modification were as follows:heating temperature40℃, pH value6.0, modification time50min. Edible films were prepared using both of the modified and unmodified gelatin and properties of the films were studied. The results showed that the modification can effectively improved the barrier properties of the films, with the peroxide inhibition activity increased from15.5%to59.4%and the water vapor permeability of the films had been reduced by20.4%. Besides, as compared with the flims unmodified, the moisture content and solubility of the film modified were reduced by7.1%and27.8%, respectively. Results of differential scanning calorimeter showed that modification with TG enhanced the characteristic temperatures of gelatin. As compared with the unmodified gelatin, the characteristic temperatures of the modified gelatin were25.7℃and56.7℃The effectiveness of edible gelatin (5%, cross-linked by TG-0.8mg/mL) coating on the quality changes of tilapia fillets at two different temperatures (0and6℃) was assessed. The gelatin coating improved drip loss compared to the untreated sample. The pH value of the fillets increased with the storage period for all the samples, with pH value at the sixth day decreased slightly. Edible coating with gelatin was effective in inhibiting bacterial growth and reducing the formation of volatile basic nitrogen and oxidation products signi-ficantly. After9days of storage under refrigeration at0℃, tilapia fillets coated with gelatin showed acceptable TVB-N concents, which was26.87mg/100g. |
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