| Whey protein isolate(WPI)is widely used as a raw material for emulsifiers and nutritional carriers in the food industry due to its good surface properties.However,under processing conditions such as high temperature,strong acid and alkali,and high ionic strength,the functional properties of WPI are easily limited.Therefore,the structural and functional properties(emulsifying properties,antioxidant properties,etc.)of WPI are improved through the interaction with polysaccharides is very important.For example,the application of WPI-polysaccharide complex in Pickering emulsion system can also effectively improve the embedding stability and delivery efficiency of fat-soluble functional factors such as curcumin and ?-carotene.This paper mainly used WPI and propylene glycol alginate(PGA)as raw materials.First,we studied the interaction mechanism of the two under different pH values and mass ratios,explored the apparent morphology,microstructure,particle characteristics,structural properties,thermodynamic properties and functional properties of WPI-PGA complex.Secondly,we used WPI and WPI-PGA complex as emulsifiers to prepare Pickering emulsions with different oil phase volume fractions(0.3-0.8),explored their physical(freezethaw,storage)and chemical properties(heat treatment,ionic strength)stability through average particle size,PDI,and other indicators,studied the stabilization effect and delivery efficiency of Pickering emulsion on ?-carotene in vitro digestion test,which provided a new idea for the application of Pickering emulsion as a delivery carrier for fat-soluble functional factors in the food and pharmaceutical industry.1.Different pH values(2.0-6.0)affect the surface charge changes of the complex coacervation process between WPI and PGA,and electrostatic interaction is the main interaction force for the complex of the two.Studies have shown that when pH = 6.0-5.0,WPI and PGA have the same charge,so they co-dissolve in the solution.At pH 4.0,WPI and PGA began to have opposite charges,and electrostatic interaction was generated to form a soluble complex,and the average particle size of the complex was the smallest at this time.At pH 3.0,WPI and PGA generated the largest amount of insoluble complexes due to more opposite charges and strong electrostatic interactions,and the Zata site on the surface of the complex was 0.The ITC data indicated that at pH = 3.5 and 4.0,the interaction between WPI and PGA proceeded spontaneously(?G< 0)and was an enthalpy-driven exothermic process.Fluorescence spectra and CD showed that the electrostatic interaction between the two increased the ?-helical structure of WPI,the secondary structure was looser,and more Trp residues were exposed.The FTIR data indicated that certain hydrogen bonding forces also existed in the complexes.2.Different mass ratios of WPI and PGA(20:1,10:1,5:1,2:1,1:1)will affect the electrostatic interaction degree of the two at pH 4.0 and the structural and functional properties of WPI.When the mass ratio is 20:1 and 10:1,the precipitation of the insoluble complex is larger,because a small amount of added PGA will preferentially interact with water and compete with WPI for water molecules,which will reduce the solubility of WPI and cause coagulation,The ?-sheet structure content of WPI was increased.With the increase of PGA,the interaction between PGA and WPI increases,and more WPI enters into the solution,so that the WPI of coagulation and precipitation decreases,the ?-helix structure gradually increases,and the ?-sheet structure gradually decreases;when the mass ratio is 2:1 When,the ?-helix structure reaches the maximum value in the whole mass ratio(20:1,10:1,5:1,2:1,1:1),which indicates that the interaction between PGA and WPI reaches saturation,at this time WPI The structure is more loose,the exposed content of tryptophan increases,and the free sulfhydryl content of the complex increases.By testing the emulsifying properties and interfacial properties,WPI-PGA complexes have better emulsifying properties,larger oil-water interface contact angle and lower surface tension than WPI;The complex with a mass ratio of 2:1 had the best emulsifying stability,an closed to 90°oil-water interface contact angle and a lower surface tension,which indicated that the WPI-PGA complex with a mass ratio of 2:1 had the potential to stabilize Pickering emulsions and even high internal phase Pickering emulsions.3.Using WPI and WPI-PGA complex(pH 4.0,mass ratio of 2:1)as emulsifiers,?-carotene-loaded Pickering emulsions were prepared with different volume fractions(0.3-0.8)of coconut oil to study their rheology Chemical properties,physical(freezethaw,storage)stability,chemical(heat treatment,ionic strength)stability and digestive stability.The rheological properties of Pickering emulsions stabilized by WPI-PGA composites show that they have more stable emulsion gel structure and elastic structure,WPI-PGA complex can stabilize Pickering emulsions with high internal phase oil phase volume fraction of 0.8.In the thermal stability,freeze-thaw stability,ionic strength stability and storage stability tests,it was found that the WPI-PGA emulsion had better physical and chemical stability,and the physical and chemical indicators showed that the stability effect was better than that of the WPI emulsion.In vitro digestion test showed that the free fatty acid release rate of the WPI-PGA emulsion was slightly lower than that of the WPI emulsion.Compared with the same emulsion,it was found that with the increase of the oil phase volume fraction,the free fatty acid release rate also increased slightly.The bioavailability of ?-carotene and the release rate of free fatty acids had similar trends,and the ?-carotene bioaccessibility of WPI emulsion was greater than that of WPI-PGA emulsion under the same oil phase volume fraction.Determination of DPPH free radical scavenging rate found that WPI-PGA emulsion had better antioxidant effect than WPI emulsion after in vitro digestion. |
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