Physicochemical Properties Of Tilapia Skin Gelatin As Affected By Acids,Sugars And Salts Commonly Used In Food

Tilapia,as one of the major economic fingerlings cultured in China,was the first of the world's aquaculture production in 2016,with 1.86 million tons of tilapia production.Tilapia fish processing industry is prosperous,the processing volume reaches 640,000 tons in 2016,producing a large number of skin by-products,and the skin is rich in protein,is the preparation of gelatin good raw materials.It can be used to supplement the deficiency of traditional mammalian gelatin due to religion(mainly Hinduism,Judaism and Islam)and other reasons in food application.Tilapia skin gelatin has good physicochemical properties similar to that of mammalian gelatin,it can be used as thickener,gelling agent,clarifying agent,emulsifier,stabilizer and so on,that is widely used in food industry.In order to develop the application of fish gelatin in food industry,it is necessary to study the effect of common food ingredients such as acid,sugar and salt on the physicochemical properties of gelatin.Although these ingredients have an effect on the physicochemical properties of fish gelatin,there is a lack of systematic research on the effects of these factors on skin gelatin.The aim of this study was to extract the fish skin gelatin from tilapia with a high extraction rate acid-alkali combination method in this laboratory,the common organic acids(citric acid,acetic acid,malic acid),sugar(glucose,fructose,sucrose),salt(sodium chloride,calcium chloride)in food were investigated by using viscosity,uniaxial compression experiment and Fourier transform infrared spectroscopy method,these components on the physicochemical properties of fish meat(mainly texture characteristics)of the changes in the law,for fish in the food industry in the production,processing and application to provide theoretical support.The research contents are as follows:1.Extract the fish skin gelatin by the optimized acid-alkali combination method,anddetermine the physicochemical properties of the fish gelatin,such as extraction rate,protein content,water content,fat content,ash content,pH value,gel strength,transparency,viscosity,molecular weight distribution of gelatin protein.The results indicated that the extraction rate of tilaplia fish skin gelatin was as high as 23.1±0.5%(w/w,based on skin weight),which was significantly higher than that of other fish gelatin in the same industry.The protein content in the finished fish gelatin is 91.5±0.5%,fat 0.5%,ash 0.2±0.0%,moisture 7.2 ± 0.3%,6.67%(w/w)concentration of tilapia fish gelatin at 620 nm transmission ratio for 86.6±1.0%,Bloom value 323.4±2.3 g,viscosity 9.23±0.25 cp,pH value 5.23±0.01.2.To explore the effects of different concentrations(0.5-2%)acetic acid,citric acid and malic acid on the viscosity,transparency and gelation characteristics of fish gelatin(2-6.67%)were studied.The results were as follows: With the increase of acid concentration,the pH of the gelatin solution decreased,the viscosity increased and the transparency increased,the acetic acid was more than malic acid and citric acid.The results of uniaxial compression showed that the true stress,true strain and Young's modulus of gelatin gel decreased with the increase of acid concentration,indicating the gel strength,elasticity and hardness decreased with the increase of acid concentration,which resulted in the decrease of gelatin gel properties.3.To explore the effects of different concentrations(5-20%)of glucose,fructose and sucrose on the viscosity,transparency,texture and structure of gelatin(2-6.67%)were studied.The results were as follows: With the increase of sugar content,the pH of the gelatin solution was not significantly changed(p>0.05),the viscosity increased,and the transparency increased.The results of uniaxial compression showed that the true stress,true strain and Young modulus increased with the increase of sugar concentration,which showed that the gel strength,elasticity and hardness increased with the increase of sugar concentration.The effect of glucose and fructose was worse than that of sucrose.4.To explore the effects of different concentrations of sodium chloride(0.1-0.5 mol/L)and calcium chloride(0.1-0.3 mol/L)on the viscosity,transparency and gelation characteristics of gelatin.The results were as follows: With the increase of NaCl concentration,the viscosity of the gelatin solution decreased and the viscosity of the gelatin solution increased with the increase of calcium chloride concentration.When the concentration of gelatin was small,the transparency of the fish gelatin increased with theincrease of the salt concentration and then decreased.When the concentration of fish collagen is 6.67%,the transparency of gelatin decreases with the increase of salt concentration,and the effect of calcium chloride on the transparency of gelatin is stronger than that of sodium chloride.The results of uniaxial compression show that with the increase of salt concentration,the true stress,the true strain and the Young's modulus of gelatin gel decrease,which indicates that the gel strength,elasticity and hardness of the gelatin are also decreasing.The effect of calcium chloride is stronger than that of sodium chloride,which has a greater influence on the gel properties of gelatin.The results of FT-IR Spectra show that with the addition of salt,the amide I with absorption peak occurred red shift,and further second-order derivative spectra showed that with the increase of salt concentration,the ?-helix content of gelatin was decreased,the ?-folding content increased,the three-dimensional network structure of fish gelatin decreased,and gelatin gel performance weakened.