Study On Constructing High Unsaturated Powdered Oil Based On Hemp Protein-based Pickering Emulsions

Powdered oil is a common food,mainly composed of lipids,carbohydrates,proteins,salts,and other raw materials.It is widely used in infant formula milk powder,non-dairy creamer,and other products.Currently,saturated fatty acid oil and synthetic emulsifiers are widely used in powdered oil on the market,which pose a certain degree of safety risks.Therefore,developing low emulsifier consumption and high unsaturated powdered oil based on the demand for healthy food has strong application value.The Pickering emulsions stabilization system has the advantages of low toxicity,less addition,high physical stability and strong biological compatibility due to the use of nanoparticles as the stabilizer.It is expected to solve the problem of powdered oil products by building a protein based Pickering emulsions system.In this study,formic acid was used as the protein solvent for the first time to prepare hemp protein nanoparticles by anti-solvent precipitation,then hemp protein nanoparticles were used to stabilize flaxseed oil Pickering emulsions,and finally spray drying technology was used to prepare the emulsions into powdered oil.(1)The effects of different concentrations of formic acid aqueous solution on the structure of hemp protein,the properties of hemp protein nanoparticles and the Pickering emulsions stabilized by hemp protein nanoparticles were investigated,and the mechanism of formic acid aqueous solution promoting the formation of hemp protein nanoparticles was explored based on the spectroscopy results.Compared with using deionized water as a protein solvent,using formic acid aqueous solution can increase the solubility of hemp seed protein by one time,which is due to the ability of formic acid to interact with and dissolve hemp seed globulin.As the increasing of the formic acid concentration in the aqueous solution,the prepared hemp protein nanoparticles suspension gradually becomes turbid,and the nanoparticle size gradually decreases to below 200 nm,the ζ-potential will also decrease to around 50 m V,and the threephase contact angle will gradually increase.Within the range of formic acid aqueous solution from 40%(v/v)to 80%(v/v),the three-phase contact angle will remain between 68.60° and90.89°;With the increase of formic acid concentration,the dynamic interfacial tension presents a trend of first decreasing and then increasing,reaching the lowest value at 40%(v/v)formic acid concentration;The formic acid concentration has no significant effect on the emulsifying properties,while higher formic acid concentration will cause the decline of foam properties;With the increase of formic acid concentration,the content of β-sheet in hemp protein first increases and then decreases,and correspondingly,the random coil content first decreases and then increases.From the fluorescence and UV-spectra,it is noted that the hydrophobic groups within the protein first mask as the concentration of formic acid increases,and then are exposed due to deconvolution;Compared with hemp protein nanoparticles,the characteristics and stability of emulsions stabilized by hemp proteins are very poor,and the characteristics of Pickeiring emulsions are also related to the concentration of formic acid.(2)On the basis of the successful preparation of hemp protein nanoparticles,the supersaturation in the process of anti-solvent precipitation was adjusted,and the effect of supersaturation on the properties of Pickering emulsions stabilized by hemp protein nanoparticles was investigated.By exploring the structural changes of hemp protein nanoparticles in the process of anti-solvent precipitation,the reason why supersaturation affected the properties of emulsions was analyzed.Three important factors,including the solvent-antisolvent ratio,the dropping rate and the stirring rate were used to adjust the supersaturation.At moderate supersaturation,such as 1:10(v/v)solvent-antisolvent ratio,a dropping rate of 15 m L·min-1 or a stirring rate of 1000 r/min,hemp protein nanoparticles exhibited smaller particle size(～130 nm),greater ζ-potential(～50 m V)and stronger wettability to water compared to hemp protein nanoparticles prepared under high or low supersaturation.Hemp protein nanoparticles prepared under moderate supersaturation exhibited more random coil(24.83%)and β-sheet(61.75%),exposing more hydrophobic amino acid residues.All O/W Pickering emulsions were able to remain stable during 3 weeks storage at 20 °C.In the presence of hemp protein nanoparticles prepared under moderate supersaturation,the emulsions exhibited larger droplet size than hemp protein nanoparticles prepared under low or high supersaturation,increasing from ～300 nm to ～450 nm.Because many hemp protein nanoparticles were separated from the interface,Pickering emulsions prepared with these hemp protein nanoparticles exhibited higher apparent viscosity than hemp protein nanoparticles prepared under low or high supersaturation.(3)Pickering emulsions stabilized by hemp protein nanoparticles was used to prepare powdered oil by spray drying.The effect of the amount of hemp protein nanoparticles on the characteristics of powdered oil was investigated,with sodium caseinate stabilized powdered oil as the control.Compared with powdered oils stabilized with sodium caseinate,powdered oil stabilized with HPNs have lower surface oil content(<6.58 g/100g),higher encapsulation efficiency(>72.86%),higher moisture content(>1.5%,w/w),better solubility(>55%,w/w),and better wettability(>700 s);The effect of different concentrations of formic acid aqueous solution on the chemical structure of powdered oil is not significant,with only slight changes in the main groups;Compared with the powdered oil stabilized by sodium caseinate,those by hemp protein nanoparticles has lower aggregation degree,smoother particle surface,and lower particle size of emulsions after re-dissolution;It is worth noting that blindly increasing the content of hemp protein nanoparticles is not only harmful to the spray drying process,but also causes the particle size of Pickering emulsions after re-dissolution to be larger and the oxidation stability to be worse;All powdered oil samples can meet conventional scenario applications,maintaining high thermal stability in the range of 0 °C to 150 °C.This study provides a practical method for the preparation of a new type of highly unsaturated powdered oil,and also expands the application range of anti-solvent precipitation as a simple and convenient method in the preparation of protein based nanoparticles.It is expected to expand the use of hemp protein,and expand the preparation method and regulation means of protein-based Pickering emulsions.