The Effect Of Modified Kgm On The Gel Properties Of Silver Carp Surimi And Mechanism For Surimi Gelation Enhancement

Surimi products are gel foods processed from surimi as raw materials,and their gel properties are an essential indicator for evaluating the quality of surimi products.The gel properties of surimi products are affected by various factors such as the characteristics of raw surimi,additives and processing conditions.Hydrophilic polysaccharides（such as starch,carrageenan,etc.）are often added to surimi products to improve the gel strength and water holding capacity.Different types of hydrophilic polysaccharides have different properties and gel-forming abilities,and there are significant differences in their effects on the gel properties of surimi.Konjac Glucomannan（KGM）is a natural neutral polysaccharide that can easily swell in water to form a viscous colloid.When the addition amount is low,KGM can improve the gel strength of the surimi,but if the addition amount is too large,it will inhibit the coagulation of the surimi.Previous experiments have found that chemical modification of KGM and proper improvement of the hydrophobicity of KGM can significantly improve the gel strength,water holding capacity and sensory quality of surimi products.However,the rules of its effect has not been systematically studied,and its mechanism is still unclear.This subject took silver carp surimi and KGM as the research objects.Based on preparing KGM modified products with different modification degrees and different hydrophilic/hydrophobic properties,and characterizing their characteristics,KGM modified products were added to surimi and prepared surimi gels.To explore the influence of other KGM modified products on the gel properties of surimi and clarify the hydrophobicity of KGM modified products on the gel properties of surimi,we studied the effect of KGM modified products with different degrees of modification on the gel properties of surimi.Furthermore,modern analysis methods were used to reveal the mechanism of KGM hydrophobicity in improving the gel properties of surimi,and a theoretical foundation was laid for regulating the texture of surimi products and developing high-quality surimi products.The research contents and results were as follows:1.The effects of modification methods and modification degrees on the physicochemical properties of konjac glucomannan were studied.Different modified degrees of konjac glucomannan-sodium acrylate polymers（KSAP）,phosphate ester konjac glucomannan（PKGM）,carboxymethlated konjac glucomannan（CKGM）,and deacetylated konjac glucomannan（DKGM）were measured for molecular weight,dispersion coefficient,radius of gyration,Zeta potential,particle size,viscosity,intrinsic modulus,contact angle,water absorption rate and solubility,to study the effect of modification method and modification degree on the physicochemical properties of KGM.The results showed that nine physicochemical properties of KGM and its four modified products could be classified into three main components:gel forming ability and hydrophobicity factor,molecular conformation factor and molecular scale factor.The modification methods and modification degrees had significant effects on the molecular properties,rheological properties and hydrophilicity/hydrophobicity of konjac glucomannan,and the modification methods had a greater impact on the physicochemical properties of KGM modified products than the modification degrees.The molecular properties of konjac glucomannan with different modification methods and degrees of modification were significantly different.Compared with KGM,the molecular weight of KSAP is increased dramatically,and the molecular weight of PKGM was significantly decreased.In contrast,the molecular weight of CKGM and DKGM had no significant change.There was no difference in the radius of gyration,and the polydispersity coefficient of the sexual products increased.The rheological properties of konjac glucomannan with different modification methods and degrees of modification are significantly different.Compared with KGM,the viscosities of KSAP,PKGM,CKGM and DKGM were significantly reduced.While the elastic modulus of KSAP,CKGM and DKGM were significantly higher than KGM,the elastic modulus of PKGM was significantly lower than KGM.The hydrophilicity/hydrophobicity of konjac glucomannan with different modification methods and degrees of modification were significantly different.Compared with KGM,the solubility of the four modified products were reduced considerably,and the contact angles of KSAP and CKGM were significantly increased.In contrast,with the increase of deacetylation degree,the contact angle of DKGM showed a trend of increasing and then decreasing.The water absorption rate of KSAP increased significantly,and the water absorption rate of the other three modified products decreased significantly.2.The effects of KGM modified products on the gel properties of surimi were studied.KSAP、PKGM、CKGM、DKGM with different modified degrees was added to the surimi to prepare surimi gels,respectively.The mechanical properties,water holding capacity,whiteness,microstructure and chemical forces of the surimi gel were measured.The effect of KGM modified degrees on silver carp surimi was studied.The results showed:（1）The grafting degree of KSAP had a significant impact on the gel strength,water loss rate,whiteness and creep parameters of the surimi gels.The breaking force,gel strength,whiteness,and cooking loss of the surimi gel in the KSAP group were significantly higher than those in the surimi gel with KGM.Compared with KGM,the gel strength of surimi KSAP with grafting degree of 52.37%,61.65%and 70.37%increased by 29.03%,36.09%and 59.65%,and its whiteness increased by 2.04%,2.76%and 2.24%,respectively.The cooking loss were increased by 27.05 times,34.14 times and 24.92 times respectively.Compared with KGM,the water holding capacity of KSAP surimi gel with grafting degree of 52.37%and 61.65%decreased by 20.88%and24.66%,respectively,and the water holding capacity of KSAP surimi gel with grafting degree of 70.37%increased by 1.44%.And the elastic modulus increased by 7.58%,14.29%and 39.06%respectively,the creep viscous flow index decreased by 37.70%,36.46%and 32.87%respectively,the stress relaxation time increased by 18.16%,13.18%and 13.39%respectively.P₂₁ was 2.18 times,2.31 times,and 2.26 times that of the KGM group,respectively,and the hydrophobic interactions were increased by 13.73%,14.76%,and 22.86%,respectively.Compared with KGM,the surimi gel added with KSAP had a denser network structure,but the water distribution uniformity was reduced.（2）The degree of substitution of PKGM had a significant effect on the puncture properties,creep properties,stress relaxation properties,water holding properties,chemical forces,degree of cross-linking and microstructure of surimi gels.With the increase of the substitution degree of PKGM,the penetration distance of the surimi gel did not change significantly,but the breaking force and the gel strength of the surimi gel gradually decreased.When the substitution degree of PKGM was 0.57%,the gel strength was the highest,and the gel strength of surimi gel was 1.97 times higher than that of KGM group.Compared with the KGM group,PKGM reduced the high creep modulus of surimi gel and the attenuation coefficient of elasticity of stress relaxation,and the added degree of substitution were 0.57%,1.31%,and 1.72%.The modulus decreased by 10.59%,5.70%,and 14.41%compared with the KGM group,and the elastic modulus of stress relaxation attenuation decreased by 98.85%,97.16%,and97.35%,respectively.The cooking loss of surimi gel added with different degrees of substitution of PKGM group increased significantly,which was 7.55 times,3.22 times,and 2.68 times higher than that of KGM group,respectively.The water holding capacity of the surimi gel in the PKGM group with the substitution degree of 0.57%and 1.31%was decreased by 20.88%and 24.66%,respectively,compared with the KGM group.Compared with KGM,the whiteness of the surimi gel in the PKGM group with a substitution degree of 0.57%,1.31%,and 1.72%decreased by 0.78%,2.15%,and1.89%,respectively.The elastic modulus increased by 97.11%,51.35%and 30.61%,respectively.P₂₁ increased by 46.14%,51.67%and 84.99%,respectively.The hydrophobic interactions increased by 41.44%,32.03%,and 24.58%,respectively.The surimi gel network structure in the PKGM group was relatively dense,and the water distribution was relatively uniform.Compared with KGM,adding lower degree of substitution PKGM（0.57%）can improve the texture properties of surimi gel.（3）Adding CKGM to surimi could significantly improve the breaking force,the penetration distance and gel strength of surimi products,and had a significant effect on the parameters of creep properties and stress relaxation properties of surimi gels.The gel strength of surimi in the CKGM group with the substitution degree of 0.21%,0.29%and 0.41%was 2.22 times,2.30 times and 1.95 times that of the KGM group,respectively.The cooking loss was 3.13 times,4.00 times,and 3.44 times that of the KGM group,respectively.Compared with the KGM group,the hydrophobic interaction increased by 53.61%,56.08%,and 48.57%,and the cross-linking degree increased by19.57%,22.77%,and 7.83%,respectively.Adding CKGM with a degree of substitution of 0.21%to the surimi can significantly increase the elastic modulus and water holding capacity of the surimi gel,and its elastic modulus is 64.19%and 247.44%higher than that of the control group and KGM group,respectively.Compared with the control group and KGM group,the water holding capacity increased by 8.56%and 12.37%.The creep modulus of elasticity increased by 11.73%compared with the KGM group.The elastic modulus of stress relaxation attenuation decreased by 92.26%,and P₂₁ and P₂₂decreased by 90.72%and 5.21%,respectively.CKGM（0.21%）can obviously improve the uniformity of water distribution and the density of network structure in surimi gel.（4）The degree of deacetylation of DKGM had a significant effect on the cooking loss,water state,water distribution,chemical force and cross-linking degree of surimi gel.With the increase of DKGM deacetylation degree,the gel strength of surimi increases significantly.When the deacetylation degree was 50.72%,the gel strength of surimi was the highest,which was 2.40 times and 3.26 times higher than that of the blank control group and KGM group,respectively.However,the gel strength of surimi products decreased when the deacetylation degree of DKGM continued to increase.The cooking loss of surimi gel increased significantly with the increase of DKGM deacetylation degree.Compared with the KGM group,the degree of cross-linking of the surimi gel with adding DKGM with deacetylation degrees of 31.07%,42.24%,50.72%,62.86%,and 72.38%increased by 5.36%,19.62%,46.21%,22.75%,and24.17%,respectively.And the cooking loss increased by-6.52%,18.67%,12.00%,26.19%and 57.65%,respectively.The water holding capacity increased by 6.84%,3.56%,5.78%,0.15%,and-10.05%,respectively,the whiteness increased by 0.10%,1.25%,1.29%,2.50%,and 2.67%,respectively.Compared with the KGM group,P₂₁increased by 4.98%,5.71%,6.30%,5.29%,and 5.08%,respectively,and the hydrophobic interaction increased by-2.67%,27.28%,57.22%,41.77%,33.77%,respectively.Compared with the KGM group,when the degree of deacetylation of DKGM was 50.72%,the creep elastic modulus of the surimi gel decreased by 10.82%,and the stress relaxation equilibrium elastic modulus increased by 16.04%.Increased distribution uniformity.（5）The results of correlation analysis showed that the gel properties of surimi products were significantly correlated with the molecular weight,polydispersity coefficient,viscosity,contact angle,water absorption rate and solubility of KGM modified products.A moderate increase in the hydrophobicity of KGM modified products could significantly improve the gel strength of surimi products.The surimi products had a higher gel strength when the contact angle was about 35°,the Zeta potential was-10～0 m V,the particle size was about 150μm,the molecular weight range was 6×10⁵ g/mol,the dispersion coefficient was about 1.5,and the elastic modulus range was 20～60 Pa,the water absorption rate was 20～50 g/g,the viscosity was200～3000 m Pa.s.3.The mechanism of the hydrophobicity of KGM in improving the gel properties of surimi was preliminarily analyzed.Myofibrillar protein,CKGM and DKGM were taken as the research objects,and were studied by means of enzymology,spectroscopy and rheology.The interaction between myofibrillar protein and polysaccharide was studied to analyze the mechanism of KGM hydrophobicity in improving the gel properties of surimi.Natural KGM significantly increased transglutaminase（TGase）activity but had no significant effect on cathepsin L activity.KGM with appropriate hydrophobicity can significantly inhibit cathepsin activity and significantly increase transglutaminase（TGase）activity in surimi.Compared with the blank control group,cathepsin L enzyme activity in surimi added with DKGM with a deacetylation degree of 50.72%and CKGM with a substitution degree of 0.21%decreased by 8.78%and 9.93%,respectively.The transglutaminase activity in the surimi DKGM group with a deacetylation degree of 50.72%was 1.08 times that of the blank control group.DKGM and CKGM stabilized the secondary structure of the protein by promoting the transformation of protein conformation fromα-helix toβ-sheet,and improved the hydrogen bond and hydrophobic interaction,thereby improving the gel strength of surimi products.