Physicochemical Properties And Stability Of Perilla Protein O/W Emulsion

Perilla is a food-drug dual-purpose plant whose seeds(Perilla seed)are generally used to extract perilla oil.The degreased perilla seed has not yet been reasonably and effectively used,and it contains more protein.Protein is an essential nutrient for the body and a macromolecular food emulsifier.It promotes the physical stability of the emulsion by reducing the interfacial tension at the oil-water interface.The stability of emulsified foods is generally improved by adding emulsifiers.The extraction of perilla seed protein to study the physicochemical properties of its emulsion can lay a theoretical foundation for the comprehensive development and utilization of perilla resources.In this dissertation,the protein isolate,albumin and globulin were obtained from degreased perilla seed.The functional properties of the three proteins were studied,the protein with emulsifying activity were selected and applied to O/W emulsion,and the effect of different factors(protein concentrations,pH,NaCl concentrations,heat treatments)on the physicochemical properties of the emulsion was studied.The main research results as follows:(1)The degreased perilla seed had a high protein content,the content of protein isolates is 87.21%,albumin and globulin are 8.52% and 13.85%,respectively.The three proteins contained the highest glutamate content and eight essential amino acids.The denaturation temperature of the globulins(103.52°C)was slightly lower than that of the perilla isolates(106.36°C)and albumin(106.84°C);the enthalpy values of albumin were the highest.Its water retention and oil retention were higher than the protein isolate and globulin.In the p H range of 2~9,the three protein dissolution showed a U-shaped curve.Globulin solubility,emulsifying activity,and foaming properties were better than albumin and protein isolates.(2)The globulin was applied to the O/W food emulsion,and the protein concentration was in the range of 0.25% to 1.25%.With the increase of the protein concentration,the droplet size of the emulsion decreased from 3.03μm to 0.9μm,and the flocculation index and the condensation index decreased.The ζ-potential decreased with the increase of protein concentration,except at 0.25% protein concentration.The content and the concentration of the interface protein gradually increased with the increase of protein concentration.During storage,when the emulsion had higher protein concentration,it showed lower creaming index and better storage stability.(3)The emulsions of pH 3~11 were prepared.When the pH was 3 and 5,droplet size,condensation index,flocculation index,creaming index and interfacial protein concentrations were higher,and the absolute ζ-potential value and interfacial protein content were lower.When pH was above the isoelectric point,with the increase of pH,the emulsion droplet size,condensation index,flocculation index and creaming index decreased gradually,and ζ-potential,interfacial protein content increased gently.During the storage of the emulsion at different pH,the oxidative stability of different emulsion varied with much difference,and the result was in accordance with the physical storage characteristics.The oxidation of the emulsion at pH 3~5 were higher than the emulsions at pH 7~11.When the pH is over the isoelectric point,the oxidation stability increased with the increase of the pH.(4)The emulsions of different NaCl concentrations were prepared(0~500mmol/L).The droplet size of the emulsions decreased and then increased.The emulsion of 50mmol/L NaCl concentrations possessed the smallest droplet size.When the NaCl concentrations was above 50mmol/L,the flocculation index increased from 7.6% to 204.95%,interface protein content and concentrations were gradually increased,and the absolute value of ζ-potential decreased.The microstructures showed obvious flocculation in emulsions.The creaming index also increased as the NaCl concentrations increased,and the addition of NaCl had an negative effect on the storage stability of the emulsion.(5)The emulsion prepared by heat treatment at 90℃ possessed the largest droplet size,flocculation index,condensation index,and the smallest absolute ζ-potential value,interface protein concentration and content,the poorest storage stability.Heat treatment at 60℃ on emulsion did not have an obvious effect on its physicochemical properties and storage stability.The droplet size,flocculation index and condensation index of emulsion at 80℃ heat treatment decreased,and the absolute ζ-potential value,the storage stability,the interface protein concentration and content increased.