Mechanism Of Protein Changes During Processing And Gelation Of Marine Fish Surimi

Marine fish is well-loved by consumers due to its high protein,low fat,and rich in essential amino acids,and its a good raw material for surimi products.There are many types of marine fish in China,and some marine fish are produced in large quantities.However,the traditional consumption habits are insufficient to make full use of marine fish resources,resulting in a low degree of processing and utilization of marine fish.Therefore,in order to find more marine fish species suitable for processing surimi,expanding the market scale,and solving the problem of pressure ponds,it is necessary to study the gel properties of various marine fish.This article studies the gel properties of a variety of marine fish,and selects fish species with larger yields and cheaper prices to study the physical and chemical characteristics of surimi processing and gel formation.The mechanism of surimi gel formation was revealed by measuring the water content,p H value,protein composition,chemical interaction between proteins,degree of protein hydrolysis,and Raman spectroscopy.In addition,myosin was extracted,and the degeneration and aggregation of myosin was studied through different processing conditions,and the appropriate mechanism of fish processing was further revealed at the molecular level.The main research contents and results are as follows:(1)In order to find more marine fish species suitable for processing into surimi gel products,45 kinds of marine fish were collected in this article.And then the surimi gel was prepared by rinsing,grinding and two-stage heating.Then,the gel strength,texture characteristics,whiteness,and water holding capacity of surimi gel were measured to find more marine fish suitable for surimi processing.The results show that the gel strength of marine fish is 163.66±2.36～1132.09±136.54 g·cm.Among them,there are14 species of fish below 300 g·cm.The cohesiveness is 0.59～0.89,the elasticity is0.84～0.99,the tackiness is 56.20-320.67 g,the chewability is 51.70～303.57 g,and the whiteness value(W)is 63.92～89.90,the water holding capacity is 70.87%～90.45%.According to the correlation analysis,the greater the gel strength,the greater the surimigel hardness and viscosity,the better the chewiness.That is,a gel with better water holding capacity and relatively good chewiness.A comprehensive analysis of the gel properties shows that Plectorhinchus schotaf、Acanthopagrus latus、Chrysophrys major Temminck et Schlegel 、 Seriola dumerili 、 Gymnothorax reevesii and Gnathanodon speciosus are suitable species for surimi production.(2)In order to better understand the mechanism of surimi gel formation,in this chapter,five kinds of marine fish are selected to compare and analyze the gel characteristics of gelled surimi and surimi gel,and the p H and moisture content of these five kinds of marine surimi during processing and gel formation are measured.The results show that compared to gelled surimi,when the stable surimi gel is formed by heating at the second stage of heating,the gel strength,hardness,tackiness,chewiness,brightness value(L *),and whiteness value(W)increase significantly.Chewability and elasticity are not significantly changed.Compared withthe first heating process surimi,the water holding capacity of Trachinotus ovatus,Acanthopagrus latus,Lates calcarifer,Perca fluviatilis surimi gel increased significantly,while the water holding capacity of Mugil cephalus surimi gel decreased.The changes in moisture content are mainly caused by rinsing and heating,and the water content of the surimi rinsing of the five species is significantly increased,and the moisture content of the surimi is reduced by heating.The rinsing made the p H of the five kinds of surimi all reach the range suitable for processing surimi.After heating,the p H of the surimi was significantly increased,but they were all within the suitable processing range of surimi(6.70 ～ 7.01).The overall research results show that during the heating process,the effect on the moisture content is relatively small,and in marine fish,the p H is within the range suitable for surimi processing after rinsing.(3)In order to further study the mechanism of surimi gel formation,sea bass and golden were selected for the study of protein-related changes.Measuried the changes in protein composition,chemical action,and degree of protein hydrolysis during surimi processing and gel formation,and combining Raman spectroscopy to study the conformational changes of proteins during process.The results showed that rinsing significantly reduced the relative content of water-soluble and insoluble proteins,and significantly increased the relative content of salt-soluble proteins(p<0.05).During grinding,the first stage heating and the second stage heating,the relative content of water-soluble and salt-soluble proteins gradually decreased to form more insolubleproteins,and the relative content of insoluble protein in the goldfish minced the second stage heatinggel was significantly greater than that of sea bass.During processing,the ionic and hydrogen bonds of the two kinds of fish gradually decrease.Hydrophobic bonds and disulfide bonds are mainly formed by heating,and non-disulfide covalent bonds are mainly formed during the first heating process.The rinsing and grinding significantly reduced the degree of hydrolysis of the protein,and the effects of heating on the degree of hydrolysis of the two fishes were inconsistent.The protein hydrolysis degree was significantly increased at low temperature heating,and the protein hydrolysis degree was significantly reduced after high temperature heating to form a stable surimi gel.The results of Raman spectroscopy showed that when sea bass and pomfret were heated to form a stable surimi gel in the second stage,the characteristic peaks of the amide Ⅰ band appeared in the wavelength range characterizing the β-sheet structure.(4)In order to reveal the protein processing characteristics at the molecular level,the myosin was extracted from the raw materials,rinsed surimi and ground surimi of sea bass and golden.And the myosin extracted from ground surimi was heated at 30,40,50,60,70 and 90 °C for 30 minutes,respectively.The results showed that the myosin turbidity of sea bass increased by 16.7% after rinsing.However,the golden mullet myosin turbidity decreased by 32.0%.Grinding and heating significantly increased the turbidity of myosin,the turbidity of sea bass myosin reached the maximum at 70 °C(0.75),and the turbidity of myosin of the golden mullet reached the maximum at90 °C(0.94).The sulfhydryl group is gradually oxidized to form disulfide bonds in the treatment process,and more disulfide bonds are formed in sea bass myosin.The surface hydrophobicity reached the maximum at 60 ℃,and then decreased,while grinding reduced the surface hydrophobicity of sea bass by 2.8%,and the surface hydrophobicity of golden carp increased by 22.2%.Infrared spectroscopy results show that rinsing and chopping myosin still retains its natural structure.During the heat treatment,the golden carp formed more β-sheet structures with increasing temperature,and the β-sheet structure content reached 52.87% at 90 ℃.For sea bass,when it is heated below 50 ℃,it mainly forms β-sheet structure,and when it is heated at high temperature,it mainly forms random coil structure(34.6%).According to comprehensive analysis,the myosin protein of different marine fish is significantly different in the degree of protein denaturation and aggregation under different external conditions.