Strength And Anisotropy Regulation Of Konjac Glucomannan/Xanthan Gum/Sodium Alginate Composite Gels

Plant-based meat simulant has been a research hotspot in recent years.Many studies have focused on simulating the structure,texture and flavor of animal protein.However,in order to fully and truly simulate animal meat,the special texture and taste provided by connective tissue can not be ignored.A lot of studies in the biomedical field have shown that synthetic polymer hydrogels have the potential to simulate connective tissue（The moisture content is low,usually 60%-80%,and most of them have anisotropic structure,with strong gel strength and toughness）.However,the edible nonanimal-derived hydrogel has high moisture content of more than 90%and prone to isotropic structure,weak gel strength and poor toughness,and can not reach the texture and taste of connective tissue.Therefore,how to improve the mechanical strength and construct anisotropic structure of edible hydrogels is a problem which needs to be solved urgently.In this study,edible hydrophilic colloidal konjac glucomannan（KGM）,xanthan gum（XG）and sodium alginate（SA）were selected as raw materials.Firstly,the effects of different freezing time,freeze-thaw（FT）cycles and water regulation on the strength of KGM/XG/SA composite gel were studied,and then the effects of pre-stretching on the strength and anisotropy structure of the composite gel were studied.Finally,the effects of cooking time on the structure and mechanical properties of the composite gel were studied with the real beef brisket fascia and porcine yellow throat as reference.The potential of KGM/XG/SA composite gel to simulate connective tissue was evaluated.The purpose of this study is to construct connective tissue analogs with excellent mechanical properties and anisotropic structure,to explore the effects of these treatments on the structure and properties of the composite gel,and to provide theoretical guidance for the regulation of gel texture.The main results are as follows:1.Freezing and moisture regulation can effectively improve the mechanical strength ofKGM/XG/SA composite gel.According to the tensile,shear and TPA test results,the elastic modulus,tensile strength,toughness,shear force,shear energy,hardness and chewiness of the frozen KGM/XG/SA composite gel increased,and the gel strength of the sample frozen at-20℃for 46 hours and FT-2 was the largest among all samples.As the moisture content decreased from 92%to 60%,the elastic modulus,tensile strength,toughness,shear force and shear energy of the samples further increased,and their maximum values were 27.1 times,12.9 times,10.7 times,3.6 times and 3.3 times of that of the non-dehydrated samples,respectively.By comparing the texture characteristics of the samples directly dried to a certain moisture content and rehydrated to a certain moisture content after drying,it was found that the latter had a greater impact on the mechanical properties of the samples and was more suitable for the moisture control of KGM/XG/SA composite gel.The result of cryo-scanning electron microscopy showed that the pore size of gel network became smaller and arranged more orderly after freeze-thaw treatment.The porous structure of gel samples after water control disappeared,forming a denser lamellar structure.LF-NMR results showed that after freezing and water regulation,T₂₁and T₂₂of the sample shifted significantly to the left,A₂₁increased and A₂₂decreased.It showed that freezing and moisture regulation were conducive to the formation of more orderly KGM/XG/SA composite gel network,reduced the fluidity of water in gel samples,and effectively improved the gel strength of samples.2.Pre-stretching treatment can construct hydrogels with excellent mechanical strength and anisotropic structure.Under the condition of the same moisture content:According to the tensile and shear test results,there was little difference between the texture indexes in the vertical direction and parallel direction of the non-stretched sample;After pre-stretching,the elastic modulus and tensile strength parallel to the pre-stretching direction were larger than those perpendicular to the pre-stretching direction,and the shear force,shear energy and fracturability were lower than those perpendicular to the pre-stretching direction.With the increase of the degree of pre-stretching,the elastic modulus and tensile strength in the direction parallel to the pre-stretching gradually increased,and the shear force and fracturability in the direction perpendicular to the pre-stretching gradually increased.The result of cryo-scanning electron microscope showed that there was little difference between the parallel and vertical microstructure of the unstretched sample;After pre-stretching,the microstructure parallel to the pre-stretching direction was more orderly than that perpendicular to the pre-stretching direction.With the increase of pre-stretching degree,the microstructure of the section parallel to the pre-stretching direction was more orderly.According to the polarizing microscope results,the POM image of FT-0 sample was completely black,indicating that it was an isotropic structure.After twice freeze-thaw treatment,the POM image brightness of the sample increased slightly,but the anisotropic structure was not obvious enough.The POM image brightness of the sample obtained after pre-stretching treatment increased significantly,and the brightness was positively correlated with the pre-stretching degree.It showed that pre-stretching was conducive to the formation of anisotropic structure of composite gel.The greater the degree of pre-stretching was,the more obvious the anisotropic structure was and the more orderly the gel network was,which resulted in the greater macro strength of gel,also confirmed by the macro weight bearing diagram.In addition,under the same tensile degree,the elastic modulus,tensile strength,toughness,shear force and shear energy of DR-60 sample were larger than those of DR-80 sample,which was basically consistent with the results of the second chapter,which further verified that moisture regulation could effectively improve the mechanical strength of gel.3.The pre-stretched samples have the potential to simulate beef brisket fascia,and the frozen samples have the potential to simulate porcine yellow throat.According to the tensile,shear and TPA test results,the texture characteristics of FT-0 samples before and after cooking were significantly lower than those of beef brisket fascia and porcine yellow throat;The texture characteristics of FT-2 samples before and after cooking were closer to those of porcine yellow throat;The tensile and TPA properties of DR-60 and DR-80samples before and after cooking were closer to that of beef brisket fascia,but the shear properties were closer to that of porcine yellow throat;The texture characteristics of the pre-stretched samples before and after cooking were closer to those of beef brisket fascia.With the extension of cooking time,the L*value of all samples gradually increased,and the a*value and b*value gradually decreased.The L*value of samples after water regulation and pre-stretching was closer to that of beef brisket fascia and porcine yellow throat.With the extension of cooking time,the cooking loss of FT-0 and FT-2 samples increased and was significantly greater than that of beef brisket fascia and porcine yellow throat,while the cooking loss of other samples decreased and was significantly less than that of beef brisket fascia and porcine yellow throat.The pore size of the gel network structure of FT-0 and FT-2 samples became larger after cooking,while the microstructure of other samples did not change significantly before and after cooking.Combined with the LF-NMR results,it could be seen that the internal water of FT-0 and FT-2 samples during cooking lost,while the gel network of the samples after moisture regulation and pre-stretching was denser,which was not easy to be damaged during cooking.This structure could bind more moisture,and the juiciness increased.In conclusion,KGM/XG/SA composite gel after freezing,moisture regulation and pre-stretching has the potential to simulate beef brisket fascia and porcine yellow throat before and after cooking.