Studies On Galic Acid-aided Soluble Myofibrillar Protein Aggregates And Their Properties

Myofibrillar protein(MP)has superior amino acid composition,high digestibility,low sensitization and other nutritional characteristics.Meanwhile,MP has natural flexible chain structure and abundant side chain active groups,which is conducive to the development of novel structurally modified fluid food.However,under neutral conditions,the excessive thermal aggregation/gelation tendency of MP in water or low ionic strength solution restricts the process and production of MP.Natural polyphenols are commonly used as antioxidants and gel crosslinkers in meat products.Due to covalent/non-covalent interactions with proteins,polyphenols can also be used to fabricate soluble protein-polyphenols aggregates to participate in the formation and stability of food structure and improve the stability of proteins.Galic acid(GA)is a kind of natural phenolic acid with small molecular weight,good water solubility and antioxidant properties.Compared with tannin with higher molecular weight,GA didn't cause excessive aggregation of protein.In this project,by adding different concentrations of GA and combining with alkaline pH shift treatment,the thermal aggregation of MP in aqueous solution was successfully inhibited,and the thermal stability of MP was improved.By adjusting the amount of GA,the MP colloid with different rheological properties was also obtained to achieve rheological and aggregation controllable.In this study,the structure and functional properties of GA-aided soluble MP-GA aggregates were further characterized,providing a theoretical basis for the development of novel protein-enhanced and low-sodium salt texture modified fluid food.The main contents and results of this study are as follows:1.GA could improve the thermal stability of MP aqueous solution,and MP colloid with different rheological properties could be obtained by adjusting the GA addition.Combined with alkaline pH shift treatment,GA could covalently bind to cysteine and tryptophan residues of MP.With the addition of GA,the amount of conjugated GA increased but conjugation efficiency decreased.The covalent binding of GA destroyed?-helix structure of myosin tail.Low concentration of GA(10 and 25 ?mol/g protein)could promote the formation of disulfide bonds and induce protein covalent crosslinking.When high concentration of GA(50 and 100 ?mol/g protein)was added,the main force of MP aggregation was transformed from disulfide bond to covalent bond between GA and MP,which formed heat-stable aggregates soluble in low ionic strength system.The covalent binding of GA and MP could shield active sulfhydryl groups and prevent the formation of disulfide bonds induced by heat treatment between sulfhydryl groups,which effectively inhibited the head-to-head and tail-to-tail binding of myosin,destroied the formation of gel network and then improved the thermal stability of MP aqueous solution.2.The physicochemical and functional properties of GA-aided soluble MP aggregates were studied.According to the results of turbidity and particle size,GA combined with alkaline pH shift treatment could significantly reduce the aggregate size.Surface hydrophobicity of GA covalently modified MP decreased and the absolute value of?-potential increased,indicating that the hydrophobic interaction of MP decreased and the electrostatic interaction of MP surface increased.Size exclusion chromatography showed that low concentration of GA could induce the formation of large molecular weight myosin aggregates.The soluble aggregates of MP induced by high concentration of GA were mainly myosin dimer.AFM images showed that GA could induce the further aggregation of hippocamp-like MP to form soluble aggregates with smaller size and higher height.In vitro digestion,compared with untreated MP,GA-aided soluble MP aggregates did not affect the final digestibility and the antioxidant activity of digest,but it reduced the digestibility in the simulated gastric juice.The low concentration of GA could induce the formation of disulfide bond,which improved viscosity and the emulsification stability of MP.High concentration of GA could reduce the emulsification stability of MP by inducing the soluble MP aggregates.