Investigating The Mechanism Of Phytosterols Photo-oxidation In Emulsions System Based On Computational Chemistry And Development Of Inhibition Techniques

Phytosterols(PS)are natural functional components that effectively reduce cholesterol levels in the human plasma,thus preventing cardiovascular diseases and fighting against cancer.However,PS is susceptible to oxidation during processing,storage,transportation,and sales due to factors such as light,heat,and metal ions,resulting in the formation of phytosterol oxidation products(POPs)that can endanger human health.In food,PS is mainly absorbed by the human body through emulsions(plant milk,beverages,sauces,etc.)and bulk oils.The oxidation of PS in emulsions is influenced by factors such as emulsion structure and pro-oxidants,which accelerate the rate of oxidation.On the other hand,PS oxidation in emulsions is predominantly driven by photo-oxidation and occurs constantly during various stages of food production,storage,and sales.However,there is a lack of research into the mechanism of PS photo-oxidation,and the reaction process and intermediates are still unclear.The impact of emulsion systems on PS photooxidation is also not well understood.To gain a deeper understanding and control of PS photooxidation,it is important to investigate the reaction principles behind the formation of POPs and the influence of emulsions on PS oxidation.In this study,PS emulsion systems were examined from the perspectives of the environment,structural composition,and interfacial properties to explore their impact on PS photo-oxidation.Molecular dynamics and quantum chemistry were employed to investigate the mechanism of PS oxidation reactions at the atomic level.Finally,based on the photo-oxidation mechanism of PS in emulsions,a new emulsion was developed to suppress the photo-oxidation of PS and enhance its stability in emulsions.1.The impact of light wavelength and sensitizers on the photodegradation of PS in soy milk emulsions was investigated in this study.After screening,PS photodegradation was induced using UVA(365-375 nm),violet(400-410 nm),blue(465-475 nm),green(530-540 nm),yellow(570-590 nm),and red(645-665 nm)light in soy milk emulsions.The photodegradation under different wavelengths was also observed in the presence of sensitizers such as riboflavin(Rb)and chlorophyll(Chl).The study found that riboflavin intensified the photodegradation of PS under UVA,violet,and blue light and led to additional formation of 6β-OH phytosterols.Meanwhile,chlorophyll caused the emulsion to oxidize more easily under red light.On the other hand,the light wavelength(UVA > violet > blue > green > red > yellow)had significant and distinct effects on PS photodegradation and the formation of phytosterol oxidation products(POPs).UVA,violet,blue,and red light induced the formation of five types of POPs,including 6α-OH,7α-OH,7β-OH,5,6β-epoxy,and 7-keto phytosterols.These results demonstrate that PS photodegradation is most apparent under UVA light and that specific wavelengths combined with light sensitizers can increase PS photodegradation in food.2.The study investigated the influence of different emulsion interfacial properties on the photooxidation of PS under accelerated oxidation by UVA irradiation.Emulsions with different interfacial properties were prepared using different types of emulsifiers.It was found that the emulsifiers had a significant impact on the photo-oxidation stability of PS in the emulsion system,with Tween 20 resulting in the highest degree of PS photo-oxidation due to its inability to generate sufficient interfacial pressure(7.49 m N/m)for physical protection.In emulsions stabilized by high molecular weight emulsifiers(HMWEs),the production of POPs was found to be correlated with the interfacial pressure and viscosity of the emulsion,with the oxidation products of β-sitosterol primarily consisting of 7-keto and 7β-OH oxidized compounds.The PS emulsions prepared with soy protein isolate-dextran mixture(SPI-Dextran)and soy protein isolate-glycosylated dextran(SPI-Gly)exhibited higher photo-oxidation stability due to their higher interfacial pressure(14.78 m N/m and 14.12 m N/m).At an appropriate emulsifier concentration(SPI-15),the interfacial pressure reached its maximum value(15.89 m N/m),resulting in lower PS oxidation and the least amount of POPs.On the other hand,the reduction in viscoelasticity of the PS emulsion led to the aggregation of emulsion droplets,exposing PS and causing additional oxidation.In conclusion,the study found that higher interfacial pressure can reduce the degree of PS photo-oxidation in the emulsion system by forming a barrier with a high-pressure interface and a strong gel-like network structure,thereby reducing PS oxidation in the emulsion.3.This study investigated the role of the oil phase composition and corresponding interfacial properties in the oxidation of PS in emulsions.Using molecular dynamics(MD)simulations,the study examined the influence of PS’s position distribution and interfacial structure on its photooxidation.It was found that in different esterification degrees(monoolein,diolein,and triolein glycerides)and chain lengths(tributyrin and trioctanoin glycerides),PS tended to distribute at the interface between the water and oil phases.The hydroxyl group at the C3 position of PS formed hydrogen bonds with water molecules,while the hydrophobic portion interacted with the oil phase through van der Waals forces.The balance between these forces resulted in the dispersion of PS in the oil phase while tending to anchor at the interface between the two phases.On the other hand,the higher viscosity(1298.5 μPa·s)and interfacial pressure(179.29 m N/m)of triolein glycerides reduced the diffusion rate of PS molecules,trapping them within the oil phase and forming micelles with water molecules that penetrated into the oil phase.The high polarity of tributyrin glyceride led to the lowest interfacial tension in the emulsion,facilitating the entry of water molecules into the oil phase and making PS more susceptible to photo-oxidation.The addition of PS increased the interfacial tension of most emulsions.The results indicated that the distribution of PS in emulsions is the main mode of its oxidation and the reason for its rapid oxidation.PS exhibited higher photo-oxidation levels in oil phases with higher polarity.4.The process of photooxidation of polystyrene(PS)was studied,and the specific reaction pathway and active sites of PS were determined through quantum chemistry(QM).The underline mechanisms of photo-oxidation were clarified,and the influence of the polarity of the phase in which PS was present on the photo-reaction was explored.The results,obtained through calculations at the M06-2X/6-311+G*-PCM //B3LYP/6-31G* level,revealed that PS photooxidation mainly occurred through a coupling reaction of the C5 radical to form 5α-OOH sterol,followed by rearrangement to form 7-OOH sterol.Additionally,a double radical reaction at the C6 position resulted in the formation of 6β-OOH sterol.By calculating the solvation free energy of PS in different solvents,it was found that an increase in solvent polarity reduced the solvation free energy of PS.On the other hand,solvents with higher polarity reduced the energy barrier for PS photo-oxidation reactions.Reactions involving singlet oxygen generally had lower energy barriers than those involving ground-state oxygen.The choice of solvent altered the pathway of the photo-oxidation reaction.5.To prevent photooxidation of PS,a new type of Pickering emulsion was developed by regulating the oriented distribution of antioxidant colloidal lipid particles(CLPs)at the oil-water interface.Various lipids and antioxidants were tested to determine their protective effect against PS photooxidation.Results showed that CLPs were capable of stabilizing Pickering emulsion and encapsulating antioxidants,providing a dual functional delivery system for PS protection.The Pickering emulsion formed had a particle size of around 350-820 nm,and the crystallization and melting temperatures of tripalmitin particles were approximately 33°C and 68.1°C,respectively.The addition of tributyrin or tricaprylin reduced the crystallization and melting temperatures of tripalmitin CLPs and improved the photooxidation stability of Pickering emulsion.The Pickering emulsion prepared remained stable for up to 12 days of light exposure.Among all tested formulations,the Pickering emulsion composed mainly of tripalmitin CLPs with added tributyrin and resveratrol had the highest photooxidation stability.In conclusion,this study provides a scientific understanding of the mechanism of PS photooxidation in emulsions and the impact of emulsion structure,offering new insights and methods for controlling PS photo-oxidation,enhancing the photo-oxidation stability of PS,and utilization.