Effects Of NaCl And Heating On Emulsifying Properties Of Myofibrillar Protein And Type Ⅰ Collagen

A phenomenon is often found in daily life: In the early stage of cooking meat,if salt is added,the broth will be clear soup,and if no salt is added,it will be white soup.The study found that there are certain differences between the two proteins,among which,myofibrillar protein and collagen have been confirmed to be the main substances involved in emulsification.However,the emulsifying effects and emulsification mechanism of these two proteins under the action of salt and heating are still unclear.Therefore,in this paper,the myofibrillar protein extracted from beef and type I collagen extracted from beef tendon and the mixed system of the two proteins were taken as the research object to explore the different Na Cl concentrations(0,0.2,0.4,0.6 mol·L-1)and heating on the emulsifying properties of the two proteins and their mixed systems were investigated.Finally,the interaction force and conformational changes of several proteins were determined by combining Raman spectroscopy at the molecular level to eveal the formation mechanism of state differentiation of cooked broth.The results can enrich the scientific theory of meat emulsification,and provide a theoretical basis for the production of emulsified meat products in the food industry.The main findings are as follows:1.The effect of Na Cl and heating on emulsifying properties of myofibrillar proteinTaking myofibrillar protein extracted from beef as the research object,the effects of Na Cl concentration and heat treatment on the emulsifying properties of myofibrillar protein were studied.The results showed that when only salt was added,the solubility,emulsifying activity index(EAI),emulsifying stability index(ESI)and emulsion viscosity of myofibrillar protein increased significantly with the increase of Na Cl concentration.When only heated,solubility,EAI,and emulsion viscosity also increased significantly,with no significant effect on ESI.When heating and adding salt,the results show that there was an intersection between the changes of solubility and EAI before and after heating between0.2-0.4 mol·L-1 Na Cl concentrations.At the concentration of 0.2 mol·L-1Na Cl and below,the solubility,EAI and ESI of myofibrillar were significantly increased when heated.At the concentration of 0.4mol·L-1Na Cl and above,the ability of inreasing solubility and emulsifying properties by heating was reduced by Na Cl,resulting in a decrease in emulsifying properties as well.The mechanism for these phenomena were : when only table salt was added,the addition of Na Cl promoted the transformation of myofibrillar from α-helix structure to β-sheet and random coil,resulting in enhanced intermolecular hydrogen bond interactions,while hydrophobic groups and the sulfhydryl groups were embedded or hidden inside the protein,which also limited the oxidation reaction between the sulfhydryl group and the disulfide bond,which was beneficial to the improvement of solubility,thereby enhancing the emulsifying properties;when only heated,the hydrogen bond content of myofibrillar protein increased,the disulfide bond was broken,which was beneficial to improve the solubility,but the hydrophobic group was exposed,and the lipophilicity was enhanced,which was beneficial to improve the emulsifying properties.When heated and salt added,at the concentration of 0.2 mol·L-1Na Cl and below,the content of hydrogen bonds in myofibrillar protein increased and the content of disulfide bonds decreased,that was,the degree of oxidation decreased,which was beneficial to the improvement of solubility,thereby enhancing the emulsifying properties.At the concentration of 0.4 mol·L-1 and above,myofibrillar protein tended to the disordered state,both myosin heavy chain and actin undergone significant degradation,the hydrogen bond content decreased,the exposure of hydrophobic groups increased,and the decreasing trend of disulfide bonds decreased,that was,the degree of oxidation decreased,which led to a decrease in solubility,and not conducive to improving emulsifying properties.2.The effect of Na Cl and heating on the emulsification properties of type I collagenTaking the type I collagen purified from beef tendon as the research object,the effects of Na Cl concentration and heat treatment on the emulsifying properties of type I collagen were studied.The results showed that: with the increase of Na Cl concentration,the solubility,EAI and emulsion viscosity of type I collagen first increased and then decreased,the emulsion particle size first decreased and then increased,and the change trend of ESI fluctuated.When the Na Cl concentration was 0.2 mol·L-1,the emulsifying properties of type I collagen were good.When heated,the solubility of type I collagen increased,the EAI decreased,the particle size of the emulsion increased,and the ESI increased.When heated and salted,the solubility,EAI and emulsion viscosity of type I collagen increased gradually with the increase of Na Cl concentration,and the emulsion particle size gradually decreased(p <0.05).When the Na Cl concentration increased to 0.6 mol·L-1,the ESI of type I collagen droped suddenly due to salting out.After adding salt,a higher concentration of Na Cl can partially degraded type I collagen to a certain extent,and the hydrogen bond interaction between protein molecules was weakened.and thiol groups were exposed to oxidation,resulting in a decrease in surface hydrophobicity and an increase in the content of disulfide bonds,as well as an increase in endogenous fluorescence intensity.These results impelled that the emulsifying properties of type I collagen became stronger after the addition of Na Cl,and then gradually deteriorated with increasing Na Cl concentration.When heated,thermal denaturation caused the unfolding of the protein structure and the exposure of the corresponding hydrophilic groups,and the hydrogen bond content increased accordingly.At the same time,the hydrophobic core and sulfhydryl groups were also exposed during heating,the sulfhydryl groups were oxidized,the content of disulfide bonds increased,the tryptophan side chain moved to the outside of the protein molecule,and the endogenous fluorescence intensity also decreased during heating.Heating made collagen type I partially denatured or degraded,and the emulsification activity was reduced,but it did not affect the maintenance of emulsification stability.After adding Na Cl,the destructive effect of heating reduced the ability of Na Cl to induce the embedding of hydrophobic groups,but high Na Cl concentration could inhibit the oxidation reaction of sulfhydryl groups and disulfide bonds during heating,thereby promoting the interaction between type I collagen and the oil phase.The emulsifying properties of type I collagen were further enhanced with the increase of Na Cl concentration.3.The effect of Na Cl and heating on the emulsification properties of the mixed system of myofibrillar protein and type I collagenA mixed system of myofibrillar protein and type I collagen in meat protein was prepared with the actual content ratio(5:1)of the two,and the effects of Na Cl concentration and heat treatment on the emulsifying properties of the mixed protein were studied.The results showed that after adding salt,the solubility and emulsifying properties of the mixed protein were similar to those of myofibrillar protein.With the increase of Na Cl concentration,the solubility and ESI of the mixed protein were gradually lower than those of the former two proteins,while the EAI was gradually higher than that of the former two proteins.two proteins.When heated,the solubility of the mixed protein decreased and was lower than that of the first two proteins.At the same time,EAI and ESI also decreased,but both were higher than the first two proteins.When heating and adding salt,after adding 0.2 mol·L-1Na Cl,the EAI of the mixed protein increased and remained stable,which was still higher than that of the two proteins.The ESI and emulsion viscosity were higher than that of myofibrillar protein and lower than type I collagen.Continuing to increase the Na Cl concentration,the solubility and ESI of the mixed protein gradually decreased,and both were lower than those of the two proteins.With the increase of Na Cl concentration,the binding between the two proteins was more tightly,and the hydrophobic group and thiol group were buried or hidden,which also limited the oxidation reaction of thiol and disulfide bond,and Na Cl induced hydrogen bond interaction Enhanced,at the same time,when the two proteins were mixed,type I collagen itself was involved in cross-linking and was destroyed to a greater extent,so Na Cl induced more of the emulsification properties of the mixed protein similar to myofibrillar protein.Heating promoted the degradation of myofibrillar protein and type I collagen to a large extent,and the mixed protein system changed from an ordered to a disordered state,resulting in a decrease in the content of hydrogen bonds and the exposure and oxidation of sulfhydryl groups.A tighter combination occurs between the two proteins,and the formed agglomerates have a certain degree of synergy in emulsifying properties,improving the emulsifying properties of the two proteins after mixing.When heating and adding salt,the addition of Na Cl increased the degree of aggregation of the two proteins,the hydrogen bond interaction was gradually weakened,the hydrophobic group and the sulfhydryl group were continuously exposed,and the tryptophan residue in the protein conformation was intramolecularly quenched.The oxidation of sulfhydryl groups broke the stability of the combination of mixed protein and oil,and inhibited the improvement effect of Na Cl on the emulsification properties of mixed protein.In summary,when only adding salt and only heating,the solubility of myofibrillar protein were both improved,so that it can show good emulsifying properties,which was conducive to the formation of "white soup";when heating and adding salt,compared with only adding salt,when adding 0.2mol·L-1Na Cl and below,the solubility and emulsifying properties of myofibrillar protein were also improved,so it was conducive to the formation of "white soup".When adding 0.4 mol·L-1Na Cl and above,the solubility and emulsifying properties were reduced,which was not conducive to the formation of "white soup",but was conducive to the formation of "clear soup".The addition of salt increased the dissolution rate of type I collagen after heating,and exposed the hydrophilic group and hydrophobic group.The improvement of the binding ability with oil-water promoted the improvement of the emulsification effect and further promoted the formation of “white soup”.After mixing the two proteins,the formation of "white soup" and "clear soup" depended on the amount of salt added.When the addition of Na Cl was less than 0.2 mol·L-1,the solubility and emulsifying properties of the mixed protein after heating were slightly improved,which was also beneficial to formation of "white soup",but when 0.2 mol·L-1Na Cl or more was added,the solubility of the mixed protein was greatly affected by the heating of myofibrillar protein,and the protein was not easily dissolved into the soup,thus inhibiting the formation of the emulsification system.It was not conducive to the formation of "white soup",thus forming a "clear soup".