Preparation And Controlled Release Properties Of Diacylglycerol-based Water-in-oil And Multiple Emulsions

Diacylglycerols(DAG)is a product obtained by esterification of glycerol with two fatty acids.As a natural component in edible oil,it is widely applied in food,medicine and chemical industries because of its excellent emulsifying properties and physiological functions such as lowering blood lipids and inhibiting the accumulation of body fat.In this paper,high internal phase emulsions(HIPEs)and water in oil in water(W/O/W)emulsions were prepared by using 1,3-DAG rich in stearic acid as both gelator and emulsifier.The stabilization mechanism of DAG and the filler effect of dispersed water droplets were clarified and the effect of internal phase composition on emulsion stability was investigated.By constructing DAG-based emulsions coloaded with hydrophilic and hydrophobic bioactive substances,the impact of emulsion composition and structure on the sustained release property,digestibility and bioaccessibility of DAG-based emulsions were evaluated.This study provides theoretical guidance for the applications of DAG-based emulsions in the food industry.The main results are as follows:(1)The effects of the aqueous phase ratios on the stability and rheological properties of DAG-based W/O emulsions were explored,and the stabilization mechanism of Polyglycerol polyricinoleate(PGPR)and DAG synergistically stabilized HIPEs was analyzed.The results indicated that,different from the network stabilization mechanism of fully hydrogenated palm oil(FHPO)emulsions,DAG can be solidified at the oil-water interface to form Pickering crystal shells to stabilize the W/O emulsion,and at least 60% aqueous phase can be stabilized.The viscoelasticity of emulsion increased with increasing water content,indicating that the dispersed water droplets acted as "active fillers",which is of great significance for the construction of low-saturation food emulsion systems.The HIPEs with 80% of water were further stabilized by synergistic effect of 6% DAG and 1% PGPR,which exhibited gel-structure and high thixotropic recovery.With the increase of PGPR concentration,the HIPEs showed decreased particle size and stability improved significantly.Moreover,the HIPEs were unable to keep stable with DAG levels >10% or < 4% due to the effects of of lipid crystal network strength to HIPEs stability.(2)The effect of polysaccharides or salts in the internal aqueous phase on the properties of DAG-based high internal phase emulsion gel was investigated,and the potential of the emulsions in encapsulation and controlled release of bioactive substances was investigated.With the presence of 1% κ-carrageenan or 0.5 mol/L NaCl in the internal phase,the HIPEs showed reduced significantly droplet size and interfacial tension,enhanced plastic structure.Moreover,the HIPEs exhibited good retaining ability for the encapsulated bioactive substances and high stability to pH environment.At the temperature close to the melting point of DAG,there were insignificant differences in terms of the release of anthocyanin under different pH environments.While the release of anthocyanin was higher from the internally-gelled HIPEs due to the disintegration of carrageenan at high temperature.At 37 ℃,the release of β-carotene was found to be slightly higher at pH 5 than that at pH 1,and the control group of HIPEs > HIPEs with NaCl > HIPEs with κ-carrageenan,which may be may be attributed to the presence of gel network structure and high adsorption of PGPR at the oil-water interface.(3)Multiple emulsions were prepared by using PGPR as the oil phase emulsifier,sunflower oil(SO)and DAG as the oil phase,and 1.25% sodium caseinate and 0.5%xanthan gum dissolved in the external water phase,respectively.The results indicate that the W/O/W emulsion has high physical stability when the concentration of PGPR was 5% and the three phase ratio was 7:3:20.Compared with the SO emulsion prepared with all-liquid oil phase,the addition of gelatin in the inner water phase could reduce the particle size of the emulsion and improve the stability of the emulsion.In addition,the effects of magnesium ion concentration and osmotic pressure changes on the stability of W/O/W emulsions were analyzed,and the results showed that the presence of fatty crystals and gelatin were effectively resistant to osmotic changes,thereby preventing water migration and delaying the release of salt ions,while the emulsion exhibited temperature-responsive.(4)W/O/W emulsion co-loaded with(-)-Epigallocatechin-3-gallate(EGCG)and curcumin were bricated,and the effects of the W/O/W emulsion structure on the encapsulation ability,bioaccessibility,and fat digestion characteristics were investigated.The encapsulation efficiency of EGCG could be improved and the release of bioactive substances during storage be effectively inhibited by adding DAG and gelatin,while the curcumin of encapsulation efficiency in DAG-SO emulsion was highest.In vitro digestion showed that the bioaccessibility of EGCG and curcumin loaded in the W/O/W emulsion was significantly improved,and the encapsulated components could be protected from chemical degradation due to oil phase structuring.In the gastric digestion stage,the presence of high melting point DAG could form a crystalline network structure,which allowed the emulsion structure to be well protected from damaging effects during digestion.After digestion of the small intestine,the W/O/W emulsion was hydrolyzed into small oil droplets,and the lipid digestibility of SO,DAG-SO and DAG-SO(Gelatin)emulsions was about 46%,33%and 38%,respectively.