| With the strengthening of people’s health awareness,much more attention has been attracted to the stabilization of functional factors.Algal oil is rich in docosahexaenoic acid(DHA),which plays an important role in human health.However,it is insoluble in water,poor stability and easy oxidative degradation to produce off-flavor,hindering the functional application in the food system.The encapsulation delivery system based on emulsion could be an effective way to solve the above problems.In this paper,algal oil emulsions were prepared using OSA starch and OSA starch-tannic acid complex as emulsifier.The effects of high-pressure homogenization parameters and the present of tannic acid on emulsion stability and flavor were studied,and the inhibition effect of tannic acid intervention on off-flavor of emulsions was explored.In addition,the relationship and the related mechanism between the proportion of tannic acid adsorbed on the interface and the stability of emulsions were analyzed,and the effect of starch matrix on the degree of off-flavor release and perception was investigated in order to improve the overall flavor properties of algal oil-loaded emulsions.In order to determine the appropriate condition for preparing algal oil emulsion,the effects of homogenization parameters(pressure 30-70 MPa,times 1-3)on the emulsion stability and flavor were studied.When the OSA starch concentration was 40 mg/m L,the homogenization pressure was 50 MPa,and the number was 2,the emulsion had good physical stability(the clarification index=0.043±0.003).However,with the increase of homogenization pressure and time,the total amount of volatile off-flavor increased by 4.62 times.The oxidation stability of emulsions showed that the lipid hydroperoxide gradually decreased by 4.76 times with the increase of homogenization pressure and time,while the malondialdehyde gradually increased by 1.40 times,indicating that the homogenization process intensified the oxidation degradation of algal oil,therefore influencing the flavor of emulsions.The inhibition effect of tannic acid intervention on off-flavor of algal oil emulsions was explored,from the point of tannic acid affecting emulsion stability to explore the reasons for differences in total amounts of volatile off-flavor.Results showed that the addition of tannic acid significantly inhibited the production of volatile flavor substances such as heptanal and(E,E)-3,5-octadiene-2-one,which were related to off-flavor.With the increase of tannic acid addition level(0-5 mg/m L),the interfacial tension between OSA starch and algal oil gradually decreased from 9.49±0.07 m N/m to 6.60±0.015 m N/m,and the proportion of tannic acid adsorbed on the interface was more than 90%.This was conducive to the rapid formation of interface films with antioxidant properties,thus effectively blocked the contact between the oil phase and initiator and delayed the oxidation,therefore improving the stability of emulsions(the malondialdehyde content<16.29±0.04μmol/kg oil after 15 days storage at 45°C in the dark).In addition,no stratification was observed after 30 days storage at 25°C for emulsions when the presence of tannic acid,and the retention rate of DHA was more than 93%.In order to further clarify the mechanism of tannic acid regulating the stability of algal oil emulsions,the reasons for the differences of emulsion stability were explored by analyzing the interaction between OSA starch and tannic acid.The Fourier transform infrared spectroscopy and the isothermal titration calorimetry suggested that the interaction between OSA starch and TA included hydrogen bonding and van der Waals forces,which was an enthalpy-driven spontaneous reaction(ΔG=-13.272 k J/mol/K,ΔH=-1.302×10~3 k J/mol,ΔS=-4.326 k J/mol/K).In addition,the hydrophobic interaction between OSA starch and tannic acid was confirmed by fluorescence spectra.The addition of tannic acid improved the apparent viscosity of emulsions,facilitated the formation of viscoelastic network structure,and limited the mobility of free water in the continuous phase of emulsion,which contributed to the improvement of emulsion stability.The microstructure showed that algal oil droplets were surrounded by viscoelastic interfacial layers formed by OSA starch-tannic acid complexes,and the continuous phase was filled by the network structure formed by complexes.The effects of starch matrix(OSA starch,OSA starch-tannic acid complex)on the degree of off-flavor release were investigated.As the key off-flavor compounds in algal oil emulsions,pentanal,hexanal,heptanal,and nonanal were selected as representation to explore the interaction mechanism between the starch matrix and aldehydes from the affinity,binding constant,and interaction force.Results showed that the binding affinities and the retention rate of aldehydes in the starch matrix decreased in the order:nonanal>heptanal>hexanal>pentanal.Compared with OSA starch,the OSA starch-tannic acid complex had a higher binding and retention with aldehydes,thereby weakening the release and perception of off-flavor.Isothermal titration calorimetry and pyrene fluorescence suggested that the interaction between the starch matrix and aldehydes was an entropy-driven spontaneous endothermic reaction,and hydrophobic interactions were the predominant driving forces.Furthermore,the reliability of the above interaction was verified by adding bond-disrupting agents. |
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