| Pea protein is a high-quality sustainable vegetable protein with a relatively balanced amino acid composition,close to the standards recommended by FAO/WHO,and contains a large amount of lysine.Pea protein is non-GMO,highly nutritious and hypoallergenic.However,pea protein has poor solubility and emulsifying property in acidic condition,which greatly limits the application of pea protein in acidic foods.Therefore,in order to improve the emulsifying ability of pea protein under acidic conditions,different types of pea protein/polysaccharide complexes were constructed based on the principle of protein/polysaccharide electrostatic interaction,and the effect of the interaction on the emulsion properties was studied.The main research contents and results are as follows:First,the effect of pea protein isolate/dextran sulfate electrostatic complex type on emulsion properties was investigated.The results of turbidity curve and phase diagram showed that the conditions for the formation of insoluble and soluble complexes between pea protein isolate(PPI)and dextran sulfate(DS)were closely related to the protein/polysaccharide ratio and pH.The conditions for the formation of soluble complexes occurred at the mass ratio of PPI/DS ≤ 2.5:1,pH 7.0～pH 4.0,the observed particle size was between 217.2 nm and 422.5nm,and the ζ-potential was between-36 mV and-55 mV;The insoluble complexes were formed at mass ratio ≥ 5:1,pH 5.0～pH 4.0,and the observed particle size was over 10 μm,and ζ-potential between-29.5mV～-35 mV.The interfacial tensions of PPI/DS soluble and insoluble complexes were higher than that of PPI alone at pH 7.0～pH 4.0,and showed decreased trend with the increase of DS content at the same pH.The emulsion stabilized by alone PPI was stable at pH 7.0 and had not creaming after storage for 14 days,while it flocculated and destabilized at pH 6.0～pH 4.0.The emulsion stabilized by the PPI/DS insoluble complexes(0.2%DS,pH5.0 and pH 4.0)immediately flocculated and destabilized.The ζ-potentials of emulsions stabilized by the PPI/DS soluble complexes were-40 mV～-60 mV,the oil droplets size was0.342 μm～1.546 μm and had no obvious change after 14 days of storage,showing good stability at pH 7.0～pH 4.0.Therefore,the formation of PPI/DS soluble complexes could significantly improve the emulsifying ability and stability of PPI under acidic conditions.Then,the effects of polysaccharide gel property on the structure of PPI/κ-carrageenan(κ-CG)complexes and the properties of emulsions stabilized by PPI/CG complexes were investigated.According to the thermal gel property of κ-carrageenan,PPI/CG microgel particles were prepared to study the effect of the complexes structure on the emulsion properties using PPI/CG electrostatic soluble complexes as control.The interfacial tension of the microgel particles was smaller than that of the soluble complexes,the interfacial contact angle of microgel particles was closer to 90°,and the emulsifying ability and stability of the microgel particles was higher.The emulsions prepared by PPI/CG microgel particles showed fluidity,with ζ-potential ranging from-37 mV to-48 mV,and remained stable after storage for 14 days at pH 7.0～pH 3.0;on the contrary,the emulsions stabilized by PPI/CG soluble complexes were solid gel-like,and the oil droplets size increased with the decrease in pH,reaching the maximum at pH 3.0,where the oil droplets aggregated.Microstructure results showed that the oil droplets of emulsions stabilized by electrostatic complexes were evenly distributed,while the particle aggregates appeared around the oil droplets of emulsions stabilized by PPI/CG microgel particles,and the content of aggregates gradually increased with the decrease of pH;with the extension of storage time,the aggregates content decreased continuously,and the microstructure of the emulsion became uniform,indicating that the disappearance of particle aggregates led to the decrease of the oil droplets size of the emulsions.The results of rheological properties showed that the elastic modulus of emulsions stabilized by PPI/CG soluble complexes was higher than the viscous modulus,and decreased with pH decreasing;while the rheological property of emulsions stabilized by PPI/CG microgel particles showed G′ < G" at pH 6.0～pH 4.0 at high frequency,indicating the viscous behavior was higher than the elastic behavior,resulting in the fluidity of emulsions.Finally,the properties of the high internal phase emulsions stabilized by the PPI/CG electrostatic complexes and the release and bioavailability of curcumin were studied.On the basis of the above studies,the effect of PPI/CG complexes on the properties of high internal phase(75%)emulsions was investigated.The study found that the oil droplets size of the emulsions prepared at pH 3.0 increased greatly after storage for 30 days,and the oil leakage rate was as high as about 4.5%;there was only a small increase in the oil droplets size of the high internal phase emulsions prepared at pH 7.0～pH 4.0 after 30 days storage.The emulsion showed no oil leakage at pH 7.0～pH 5.0,and only slightly oil leakage occurred at pH 4.0;microscopic results showed that the oil droplets were highly tightly packed state,and the emulsion structure was similar to the gel network structure.All high internal phase emulsions had higher G′ than G″ with frequency sweep.The G′ was lower than G″ under high stress,resulting the gel structure destroyed,and the yield stress decreased with the decrease of pH.The bioavailability of curcumin encapsulated in the emulsion ranged from 33.7% to 44.5%,which was higher than that encapsulated in the sunflower oil(25.8%).Therefore,high internal phase emulsions stabilized by PPI/CG complexes loaded with curcumin could improve its bioavailability. |
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