Molecular Mechanism Of Self-assembly Structure Formation In Phytosterol Based Binary Oleogels And Their Controlled Release And Delivery

As an alternative to traditional plastic fat,oleogels not only have the characteristics of plasticity,low saturated fat and zero trans fatty acids,but also have the functions of controlling release,regulating lipid digestion and improving the bioavailability of fat-soluble active substances,which has attracted extensive attention in the food industry in recent years.However,one gelator-based oleogels not only have limited gelation ability but also are sensitive to processing conditions.The multi-component oleogels have higher gelation ability and rheological properties,and their structural properties are obviously better than one gelator-based oleogels Currently,the formation of multi-component oleogels were randomly compounded in the experiment.The formation mechanism of multi-component oleogels and the relationship between structural properties and controlled release and delivery behavior was also unclear,which greatly limited the development and application of novel oleogels.Therefore,in this paper,three different types of gelatros were selected to compound withβ-sitosterol respectively to construct binary oleogel systems.Firstly,the interaction force between oleogelator and the difference of self-assembly mechanism in binary oleogels system were studied from the molecular level.Moreover,the effects of oil phase composition and properties on the formation,microstructure and mechanical properties ofβ-sitosterol based oleogels with different self-assembly mechanisms were investigated,and the internal laws of oil phase composition and properties on different self-assembly structures were clarified.On this basis,the binary oleogels were used as the delivery carrier,and the influence mechanism ofβ-sitosterol base binary oleogels self-assembly structure on flavor substance release and the stability and bioaccessibility of bioactive substance were investigated to clarify the relationship between the self-assembly mechanism of phytosterol based oleogels and their functional properties.The main results were shown as follows:（1）Molecular mechanism of self-assembly structure formation inβ-sitosterol based binary oleogelsBinary oleogels systems（SO,SL and SM）were formed by combiningγ-oryzol,lecithin and monoglyceride withβ-sitosterol,respectively.The effects of oleogelator molecular structure differences on intermolecular interactions,molecular packing and supramolecular self-assembly structure were investigated through MD,FTIR,XRD,SAXS,DSC and PLM.Results showed that the interactions betweenβ-sitosterol andγ-oryzol,lecithin and monoglyceride include hydrogen bonding,van der Waals force and desolvation,among which van der Waals force and desolvation play the dominant role.Whenβ-sitosterol was mixed withγ-oryzol,lecithin and monoglycide,stable oleogels were formed.XRD,SAXS and PLM analysis showed that the three groups of oleogels were structured through varied self-assembly mechanisms.In the SO binary oleogel system,the number of characteristic diffraction peaks ofβ-sitosterol decreased and the order structure of the system decreased,forming a self-assembled fiber network structure.In SL binary oleogel system,the characteristic diffraction peak ofβ-sitosterol did not change after lecithin was added,but the microregion size ofβ-sitosterol self-assembly in the oil phase increased.In the SM binary oleogel system,there were not only the corresponding characteristic diffraction peaks ofβ-sitosterol and monoester,but also a new diffraction peak at 4.6?,forming a new layered self-assembly structure.（2）The effect of oil phase matrix on the self-assembly structure ofβ-sitosterol binary oleogelsMedium chain triglyceride,sunflower seed oil and linseed oil were selected to prepareβ-sitosterol based binary oleogels.Sunflower oil has the lowest permittivity among the three oils.The smaller the dielectric constant of the oil phase,the higher the aggregation temperature corresponding to the formation of the self-assembled structure of the oleogels.Thermodynamic calculation of self-assembly showed that the formation of self-assembly structure ofβ-sitosterol based binary oleogels were driven by enthalpy and had higher thermodynamic stability in sunflower oil.The XRD results showed that there were no new crystallization peak in the three oil phases of differentβ-sitosterol based binary oleogels.The crystal morphology of threeβ-sitosterol based binary oleogels were significantly affected by the different oil phases.Theβ-sitosterol based oleogels had lower crystallization induction time,microviscosity,relaxation time,and higher hardness and viscoelastic properties in sunflower oil matrix,followed by linseed oil and medium-chain triglyceride.The relationship between oil phase characteristics and macroscopic properties ofβ-sitosterol based binary oleogels was analyzed by pearson correlation.The results indicated that the permittivity of oil phase was highly positively correlated with the thermodynamic parameters of self-assembly,crystallization induction time,fluorescence intensity of molecular rotor and adhesion of lipid gel,and negatively correlated with aggregation temperature,hardness and viscoelastic properties.The low permittivity of sunflower oil was beneficial to the formation the network structure ofβ-sitosterol based oleogels.（3）Release regularity and controlled release mechanism ofβ-sitosterol based binary oleogels on flavor substancesThe Controlled release mechanism ofβ-sitosterol based binary oleogel systems on five typical volatile flavor compounds was studied.The release capacity of 5 flavors was as follows:2,3-butanedione>leaf alcohol>limonene>linalool>ethyl octanoate.The results of dynamic release headspace analysis showed that the maximum headspace concentration and release rate of flavor substances inβ-sitosterol-based binary oleogels were lower than those in non-gelated oil,which indicated thatβ-sitosterol-based binary oleogel systems could achieve the sustained release of flavor compounds.Among them,SO had the strongest retention effect on volatile flavor substances,followed by SL and SM.The release amount and release rate of flavor substances were highly correlated with the oil binding capacity and composite modulus of oleogels.Static headspace analysis and thermodynamic calculation showed that the partition coefficient(K_a/o)of five volatile components in SO was the lowest and the enthalpy of affinity was the highest,which indicated that the self-assembled structure of oleogels played a major role in controlling the release of flavor substances.In addition,the K_a/o values of 2,3-butanedione were significantly different inβ-sitosterol based binary oleogel,but the K_a/o values of ethyl octanoate and limonene were less affected,which may be related to the interaction between the oleogels matrix and volatile molecules.（4）The protection and delivery characteristics ofβ-sitosterol based binary oleogels for astaxanthinβ-sitosterol based binary oleogels were used as delivery carriers of astaxanthin,and the effects ofβ-sitosterol binary oleogels with different self-assembly structures on stability and bioaccessibility of astaxanthin were investigated.The results showed that the network structure formed byβ-sitosterol oleogels could effectively reduce the crystallization of astaxanthin.Under UV light and different storage temperatures（4℃and 25℃）,the retention rate of astaxanthin in the oleogel systems were higher than that in the ungelated oil phase,which indicated that theβ-sitosterol based oleogels structure could provide a better protective effect for astaxanthin.The protective effect of three differentβ-sitosterol based binary oleogels on astaxanthin was as follows:SO>SL>SM.The results of in vitro simulated digestion showed that the bioaccessibility of astaxanthin in SM was the highest（58.13±2.03%）,followed by SL,Control and SO.Pearson correlation analysis showed that the bioaccessibility of astaxanthin was highly positively correlated with lipolysis level（P=0.981）.Analysis of micelle fatty acid composition showed that SM and SL had higher fatty acid content,and the hydrolysis and emulsification of monoglycide and lecithin promoted the formation of micelle structure.The results of kinetics of lipolysis and thermodynamics of lipase reaction showed that the oleogels structure in the oil phase would affect the interface adsorption of lipase and reduce the rate of lipolysis.The bioaccessibility of astaxanthin was affected by both oleogelator composition and self-assembly structure of oleogels.