Preparation And Characterization Of Oleogel Based On Protein-Polyphenol Colloidal Complex

Oleogel is a system containing a high concentration of oil(above 90%),with a thermoreversible three-dimensional network entraped the liquid oil by using gelator agents to provide a solid character.Oil gelation can reduce the use of trans fats in foods,increase the content of polyunsaturated fatty acids,and act as delivery system for hydrophobic nutritional and bioactive compounds.Therefore,it has good application prospect.The traditional gelator agents include phytosterol,biological wax,hydroxylated fatty acid and ethyecellulose,etc.However,these gelator agents still exist many problems,such as the gel properties of phytosterols were seriously affected by water,using ethyecellulose to prepare oleogel requires high temperature process which will cause oxidation.Hence,the key problem of oleogel preparation is the search and use of new gelator.The food grade polymer(protein,polysaccharide,etc.)has a high yield and variety,and has high nutritional value.It has a great scientific significance to discuss the preparation of oleogel by natural polymer.We used gelatin and polyphenol to prepare colloidal complex,and the emulsion was prepared using colloidal complex as emulsifier,then we prepared oleogel by drying the emulsion.We studied rheological and application property of oleogels,and discussed the effect of polysaccharide on the properties of oleogels.The main contents are as follows:(1)The preparation and characterization of gelatin-polyphenol colloidal complexes were studied.We prepared gelatin-polyphenol colloidal complexes by selecting B-type gelatin and tannic acid or grape seed proanthocyanidin,and investigated the effects of pH and polyphenol concentration on the properties of complexes.We characterized their particle size,Zeta potential,light transmittance,morphology,antioxidant activities and interfacial adsorption kinetics,and analyzed the binding process by fourier transform infrared spectroscopy and isothermal titration calorimetry.As the results shown,gelatin and polyphenol can form stable colloidal complexes under pH 6,and it was mainly hydrogen bonding.The secondary structure composition of gelatin was modified after complexing with polyphenols,and the antioxidant activity of the gelatin solution was effectively enhanced by forming colloidal complexes.What's more,the gelatin-polyphenol colloidal complex has a good ability to reduce interfacial tension.(2)The oleogel prepared with gelatin-polyphenol colloidal complex was investigated.Emulsion was prepared by colloidal complex and soybean oil,then complete remove the water phase of emulsion by oven-drying and freeze-drying to obtain the dried product.Then the dried product was sheared to prepare oleogel sample.The gelatin-polyphenol colloidal complex could effectively inhibit the lipid oxidation of emulsion during storage.The oleogel could prepare by complete removal of the water phase of the emulsion which stabilized with colloidal complex by freeze-drying,and the oleogel showed ‘solid-like' behavior.However,the emulsion couldn't form oleogel by oven-drying.(3)The effect of polysaccharide on the stability of emulsion and oleogel was discussed.We selected flaxseed gum added to the emulsion which prepared by gelatin-polyphenol colloidal complex and soybean oil to obtain a multi-layer emulsion,then use it to prepare oleogel.As the results shown,oleogel could obtain by oven-drying after added flaxseed gum,and oleogel prepared by oven-drying was softer than prepared by freeze-drying,and microcosmic and macroscopic forms were also different.The oleogel prepared by freeze-drying or oven-drying both showed solid behavior,as well as a certain degree of thixotropic recovery and the ability to redistribute emulsion.(4)Soybean oil,flaxseed oil and canola oil with different fatty acids composition were chosen as oil phase to produce oleogel,and the rheological properties and oxidation stability during storage were measured.And the loading efficiency of ?-carotene of the oleogel was evaluated.As the results shown,the oleogel could be prepared by different oil phase with different unsaturated fatty acids,and all of them showed solid behavior.In the storage process,the rheological change of oleogles prepared by flaxseed oil and canola oil was less than oleogels prepared by soybean oil.While the oxidized stability of oleogels prepared by flaxseed oil is lower than that of soybean oil and canola oil.In the process of external simulation,the release rate of fatty acids and the bioavailability of ?-carotene of the oleogels were higher than that of the corresponding vegetable oils.That indicated the release rate of fatty acids and the bioavailability of ?-carotene were improved for the oleogels.