| In this paper,the defatted Pseudosciaena crocea roes were used as raw materials to prepare roes protein hydrolysates by enzymolysis modification technology.The emulsification and anti-oxidation properties of the enzymatic modification products of roes protein were explored and their possible mechanisms were studied.The oil-in-water nanoemulsions were prepared using this emulsifier to further study the physical stability and oxidation stability of the emulsions.The theoretical basis for the development of protein-based natural emulsifiers using Pseudosciaena crocea roes as raw materials is provided.The research content and results are as follows:1.Trypsin,alkaline protease,papain,and flavor protease were used to hydrolyze the defatted Pseudosciaena crocea roes,respectively.The effect of enzyme type on the emulsifying activity and emulsion stability of the hydrolysates was investigated.The results showed that hydrolysates prepared by papain possessed the best emulsifying capacity.During the enzymolysis,it was found that the enzyme inactivated by high-temperature can significantly reduce the emulsifying capacity and solubility of the final hydrolysate compared to mild inactivating method.In addition,hydrolysates with different degrees of hydrolysis were prepared by using papain and by controlling the enzymatic hydrolytic time,and the emulsifying and antioxidative properties of these hydrolysates were investigated to find the fish egg hydrolysates with optimal emulsifying capacity and good oxidation resistance.It was found the hydrolysate with degree of hydrolysis of 4.68%showed the best emulsifying capacity.The emulsifying activity and emulsifying stability of the hydrolysate reached 85.27 m2/g and 24.84%,respectively,which was close to the emulsification of sodium caseinate.At the same time,this hydrolysate possessed good antioxidative ability.Therefore,the hydrolysate with degree of hydrolysis of 4.68%was used to prepare the subsequent emulsion.2.Ultrasonic method was used to prepare emulsions and hydrolysates with different degrees of hydrolysis were used as emulsifiers.The properties and physical stability of the emulsions were studied to optimiz the hydrolysates of fish eggs which can be used in emulsion systems.At the same time,the physicochemical properties of the hydrolysates of fish roes with different degrees of hydrolysis and the relationships between structure and function were discussed.The results are showed as follows:(1)The particle size,?-potential,rapid stability,emulsion stability,and microstructure were determined to reveal the influence of hydrolysates with different degree of hydrolysis on the physical stability of O/W emulsions.It was found that the emulsion prepared with the hydrolysate with a degree of hydrolysis of 4.68%has a good physical stability and can be used as the best emulsifier in the emulsifying system,this result is consistent with the above results of emulsifying activity and emulsion stability.(2)By comparing the physicochemical properties of hydrolysates with different degrees of hydrolysis,it was found that papain teatment can significantly improve the solubility and surface hydrophobicity of the hydrolysates.All hydrolysates showed good thermal stability,and the degree of denaturation increases with the degree of hydrolysis.Appropriate control of the hydrophobicity of the surface and the expanding of the peptide chains contributes to the improvement of its emulsifying capacity.(3)The amino acid composition and molecular weight distribution of hydrolysates were measured to investigate the influence of the primary structure of the hydrolysates on the emulsifying capacity.As a result,it was found that the ratio of the hydrophobic amino acid to the hydrophilic amino acid and the molecular weight distribution had a significant effect on the emulsifying property of the hydrolysates.Appropriate ratio of hydrophobic amino acid to hydrophilic amino acid contributes to the improvement of emulsifying capacity.When the proportion of peptides was at a molecular weight distribution of 1 to 10 kDa,the emulsifying capacity is good,and the hydrolysate has good emulsifying properties.It is presumed that molecular weight of the peptides at this range play an important role on the improvement of emulsifying.(4)Fourier transform infrared spectroscopy was used to study the changes of amino acid groups and peptides in hydrolysates with different degrees of hydrolysis.It was found that there was a group of strong absorption peaks near 1655 cm-1 in the amide I region.During hydrolysis,the peak position moves to the high-wavelength region which indicated that the hydrogen bonds and a-helical structures maintaining the three-dimensional network structure between different peptide chains of hydrolysates were destroyed.In the amide A band,a strong set of absorption peaks appear in each sample,and during hydrolysis,the peak position moves to the low-frequency band which indicated that the-NH group in the peptide chain is involved in the formation of hydrogen bonds.During the enzymatic hydrolysis,more-NH groups appear and the hydrogen bonding gradually increase.In the amide B band,two groups appeared which represented the absorption peaks of the asymmetric-CH and NH3+ hydrophobic groups.The peak position shifts to a lower band with increasing degree of hydrolysis,indicating that the hydrophobic groups inside the protein were continuously exposed during the enzymatic hydrolysis.(5)The content of secondary structure was determined by two-dimensional chromatography.It was found that the secondary structure of the hydrolysates was dominated by ?-sheets and random coils.With the development of enzymatic hydrolysis proceeding,the content of ?-sheets and random coils increased,and ?-bend was reduced,and the a-helix structure is completely destroyed.The peptide chain is in an expanding state,and the structure of peptides in the hydrolysate underwent the changes from order to disorder,and the flexibility of the molecule increased,which contributes to the adsorption of the protein at the interface.3.The ultrasonic method was used to prepare O/W emulsions with the hydrolyzed fish roes hydrolysate of 4.68%.The effects of the amount of hydrolysate,pH,and oil phase volume fraction on the properties and physical stability of the emulsion were studied in order to optimize the preparing condition of the O/W emulsions,.It was found the stable emulsion could be obtained under the condition of 3%hydrolysate,pH 7,and 10%volume fraction of the oil phase.4.Using Fenton catalytic oxidation system to simulate oxidation and using sodium caseinate as control,the emulsions were prepared by hydrolysates with a degree of hydrolysis of 4.68%and 6.80%.and the oxidation stability and physical stability of these emulsion were examined during storage by determination of the peroxide value and the secondary oxidation product of the oil in emulsion.The results showed that these emulsions presented good physical stability during storage.Hydrolyzates with 4.68%hydrolysis degree and 6.80%hydrolysates can inhibit the production of aldehydes and alcohol oxidation products in the emulsifying system.These hydrolysates showed a certain antioxidative activity by scavenging free radicals and chelating metal ions in the emulsion system. |
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