| China is the largest producer and exporter of tilapia in the world. As one of Chinese major foreign exchange earner of freshwater fish, tilapia is also the first foreign exchange earner of agricultural products in Hainan, and it is mainly exported in the form of frozen tilapia fillets and frozen whole fish. Processing of frozen tilapia fillets produces a lot of by-products, including the fish head, fish skin, fish bone, fish offal and fish mince, and the weight of them is about 40%-55% of raw fish. Only a small portion of these by-products is processed into fish meal and other low-value products, most of the by-products are discarded, resulting in a serious waste of fish resources and serious pollution of the surrounding environment. So it is necessary to study the development and utilization of the by-products of the processing of frozen tilapia fillets. In this study, tilapia fish skin and fish mince were selected as raw material and the effects of gelatin extracted from fish skin used in tilapia surimi products made offish mince were studied. The main research contents and results were as follows:1 Preparation of tilapia fish skin gelatin and its basic property measurementsGelatin was extracted from tilapia fish skin using hot water method, and its component and basic properties were measured. The results showed that tilapia fish skin gelatin extraction rate was 27.08%, with a purity of 85.02%. Its protein content was (84.74±0.41)g/100g, crude fat content was (1.13±0.016) g/100g, water content was (13.17±0.36) g/100g and ash content was (0.97±0.11)g/100g. Its pH was 6.97. Its isoelectric point was about 4.5. Its molecular weight was mainly above 72,000 Dalton. The gel strength of 6.67%(w/v) of fish skin gelatin was 325 g. UV absorption peak of fish skin gelatin (0.25 mg/mL) was 211.5 nm.2 Formulation of tilapia fish mince surimi products with the adding of gelatinFish mince was made into surimi with the addition of salt, hydroxypropyl starch, saccharose and gelatin. The effects of gelatin and other additives were explored in single factor experiments, and the formulation was optimized by orthogonal experiment. It was confirmed that the best surimi product formulation was:2% salt,2% saccharose,10% hydroxypropyl starch,15% gelatin solution (the percentage of fish mince weight). Under this condition, the sensory quality of surimi product was well and the product was low in fat and high in protein. It was a kind of healthy food which had good taste and nutritional value. Then the quality of the surimi product was measured, including physical testing, chemical testing and microbiological testing. Results showed that its protein content was 34.86%, crude fat content was 1.05%, water content was 61.45% and ash content was 1.87%. The total number of colonies was 4.7×104 CFU/g, coliforms were 410 MPN/100 g, and pathogens were not detected. These results were in line with national standards. Compared with the surimi product which was made of tilapia fish meat, the surimi made of fish mince exhibited lower whiteness but equal quality in other aspects.3 Effect of perilla seed oil on the quality of tilapia surimi productsThe effects of perilla seed oil on the quality of tilapia surimi products were investigated by testing the texture, gel strength, expressible water and color of the surimi products. Results showed that the addition of perilla seed oil decreased the hardness, gumminess, chewiness, breaking force but increased the expressible water of the tilapia surimi products. The elasticity and cohesiveness of the surimi products changed little. On the other hand, lightness and b* of the surimi products increased, a* showed a tendency that increased at first and then decreased. The whiteness of the surimi products increased.4 Effect of Tilapia fish skin gelatin on the quality of tilapia surimi products adding oilFish skin gelatin was added to tilapia surimi products which had been added in Perilla seed oil. Then product structure, gel strength, expressible water content and color were detected to explore the effect of tilapia fish skin gelatin on the quality of tilapia surimi products adding oil. The results showed that when the gelatin concentration was below 4%, the effects were similar to the effect of perilla seed oil on the quality of tilapia surimi products but when the gelatin concentration was above 4%, the texture, gel strength and color of the sample were improved, water retention of the sample was good, thus it may be known, adding fish gelatin appropriately could improve surimi products quality.5 Effect of adding Golden pompano fish on the quality of tilapia fish surimi productsThe gel forming ability of Golden pompano fish surimi is higher than tilapia fish surimi. Golden pompano fish was added to tilapia fish surimi to explore the variation of tilapia surimi quality. The product structure, gel strength, expressible water content and color of tilapia surimi were detected. The results showed that the higher the content of Golden pompano was, the better the quality of surimi products were. Along with the rising of the content of Golden pompano fish, the hardness, gumminess, chewiness, elasticity, cohesiveness, gel strength and whiteness of the sample increased, but expressible water content had no significant changes. The results showed that adding Golden pompano fish in a certain extent could improve the quality of tilapia surimi.6 Effect of adding tilapia fish skin gelatin on the quality of mixed surimi productsTilapia and Golden pompano fish mince were mixed in a certain proportion, then different amounts of gelatin were added. The structure, gel strength, expressible water content and color of the sample were detected. The results showed that adding gelatin to the mixed surimi products led to a significant improvement of the quality of surimi, such as increased its hardness, gumminess, chewiness, whiteness and gel strength. Its expressible water content decreased. The elasticity, cohesiveness, broken distance showed a little change. |
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