Fabrication And Characterization Of Functional Soy Protein-based Nanoparticles Using Subcritical Water Technology

To improve the solubility and bioavailability of some active substances,this study tried to construct stable and efficient nanoparticles using soy protein isolate(SPI)as a carrier.As we know,the colloidal and physicochemical properties of nanoparticles were strongly influenced by protein structure.Subcritical water(SW)treatment(100-374°C)could modify the structure of protein and dissolve hydrophobic active ingredients.Based on SW technology,protein-based active nanoparticles enriched with hydrophobic ingredients(phytosterol and rutin)were fabricated,and their physicochemical properties,stability and digestibility were evaluated.Our study may provide a theoretical basis and new way for developing protein base functional foods enriched with active ingredients.The main conclusions were as follows:(1)The effects of conventional heat treatment(90°C)and SW treatment(120°C)on the aggregation behavior and the interfacial activity of soy protein isolate(SPI)were studied.Compared with SPI90,SW protein had larger aggregate size and lower polymerization ratio,and its surface hydrophobicity was lower.The adsorption rate and adsorption strength of SPI120 at the air/water interface were significantly higher than that of SPI90,and are not affected by the degree of aggregation.This may be related to the lower polymerization degree of SPI120 and the more flexible molecular structure.The higher interfacial activity of SPI120 was conducive to the formation of visco elastic interfacial film,which significantly improves the foaming ability and foam stability of protein.The high degree of aggregation of protein molecules significantly degraded their foam properties.(2)In this study,sodium caseinate(SC)and SW soybean protein were used as stabilizers to construct SPI-PS nanoparticles with strong stability,high entrapment rate and low crystallinity,and their colloid and digestion properties were characterized.Compared with SC(188.5nm),the particle size of natural SPI nanoparticles was larger(212.2nm);heat treatment,especially the SW treatment(150.0nm)significantly reduced the particle size of particles,and significantly increased the entrapment and load of sterols,and the storage and stability of heat resistance increased significantly.It was speculated that the SW SPI has a flexible molecular structure and a higher interfacial activity.More phytosterol molecules were loaded inside the protein aggregates at the moment of phytosterol anti solvent,and the sterol molecules and proteins have a surface binding to the tightly structured natural SPI.In vitro digestion results showed that the particle size of PS nanoparticles increased rapidly after digestion in vitro,which resulted in a decrease in the bioavailability of the particles.(3)In order to improve the bioavailability and acid stability of SPI-PS nanoparticles,the Arabia glue-SPI120-PS core-shell nanoparticles(pH 4.5)were fabricated by compound coagulation method with Arabia glue as a stabilizer.Arabia gum can obviously reduce the particle size of SPI120-PS at pH 4.5,improve the encapsulation efficiency and load of nano particles,and this improvement effect was directly proportional to the amount of the addition of Arabia glue.Compared with SPI120-PS,Arabia gum could significantly improve the thermal stability of nanoparticles,delay the release rate of sterols and the speed of protein digestion,and improve the bioavailability of phytosterols.(4)In view of the high solubility of the hydrophobic polyphenols under the SW condition,it is assumed that more polyphenols can be combined with the denatured protein in the process of heating and cooling,and the SPI-rutin mixed solution is heated directly by SW to induce the two groups to be co assembled,and eventually obtain SPI-rutin nanoparticles.Under SW conditions,proteins could effectively protect rutin molecules from degradation.SW treatment significantly increased the binding capacity of SPI to rutin,and the presence of rutin inhibited the formation of two sulfur bonds in the process of protein aggregation.In the emulsion system,protein and rutin were adsorbed together at the oil/water interface to form a thick interface layer with high protein and rutin content,which significantly improves the storage stability and oxidation stability of the emulsion.