Studies On The Application Of Skin Gelatin In Fresh-water Fish Surimi-based Products

Fresh-water fishes that are abundant in China, has become a major source for producingsurumi-based products to replace marine fishes. However, deep-processing of fresh-water fisheswas restricted, due to their low meat-obtain ratio and poor gel-forming ability. It has been foundthat the gelling properties of fresh-water fish surimi could be improved by adding food additivessuch as hydrophilic gel and starch, while the protein content and nutritional value of productswere decreased simultaneously, which went against the purchase intention of the customers. Onthe other hand, the gelatin prepared from fish skin was reported to exhibit excellent gel-formingability. Therefore, the gelatin was extracted from fish skin, and the effect of adding them infreshwater fish surimi gel was also investigated in this study.In this research, the gelatin was extracted using hot water extraction and enzymolysis fromtilapia skin which had been pretreated with acid and alkali. The content of protein, fat and ash,the amino acid composition, the molecular weight distribution and the gel-forming ability of fishskin gelatin were determined. The effects of adding skin gelatin and its enzymolysis productswith different molecular weight on surimi gel properties including gel strength, texture profileand analysis (TPA) and water binding capacity were investigated. The mechanism of skin gelatinaffecting on surimi gel properties were analyzed by SDS-polyacrylamide gel electrophoresis,chemical binding force and the microstructure observation with paraffin sectioning organization.Firstly, the present study was undertaken to prepare and characterize the gelatin from tilapiaskin and their influence on the gel properties of silver carp surimi was also investigated. Theessential amino acid and flavor amino acids of tilapia skin gelatin accounted for24.3%and56.8%of the total amino acid repectively, indicating that the obtained gelatin had nutritionalvalue to some extent. The breaking force and hardness of surimi gels were increased by20%and31%respectively with the addition of the gelatin at10%(w/w) of surimi protein. Furthermore,the water holding capacity of surimi gels was also improved by adding skin gelatin. Based on theresults of protein solubility of surimi gels in various protein denaturant solutions and SDS-PAGEof the soluble fractions, suggesting that the main force involved in the interaction of gelatin andsurimi protein was ionic bonds, thus improving surimi gel-forming capacity.Secondly, the changes in the gel properties of silver carp surimi by adding the skin gelatinwith different molecular weight distribution were determined. The breaking force, hardness andwater holding capacity of freshwater surimi gels were improved by adding skin gelatins withhigh molecular weight at the concentration of10%(w/w) of surimi protein. However, no obvious changes in the physical properties of surimi gel were observed by adding skin gelatinswith low molecular weight. The electrophoresis study of the soluble fractions in proteindenaturant solution and the Paraffin wax biopsy observation of surimi gels were determined,indicating that skin gelatin with low molecular weight can fill into the network of surimi gels andmaybe hinder the cross-linking between myosin heavy chain and actin, but the cross-linking wasnot easily interfered by adding skin gelatin with high molecular weight.In conclusion, skin gelatin with high molecular weight exhibited good gel-forming abilityand could be interated with water-soluble protein of surimi through ionic bonds, resulting inimproved gelling properties of fresh-water surimi. However, the formation of surimi gel networkwas interfered with high molecular gelatin. On the other hand, the effect of skin gelatin with lowmolecular weight on the properties of surimi gel were not observed, while the dense network ofsurimi gel could be obtained by adding them. Therefore, this study results indicated gelatinextracted from fresh-water fishes could be used as the materials to prepare the quality improverof fresh-water fish surimi products, thus fulfill the demand of surimi products with good qualityfor customers.