Study On The Construction And Bioaccessibility Of High Internal Phase Emulsions With High Load Of Curcumin

Curcumin is a kind of polyphenols extracted from turmeric plant roots contained a variety of physiological function,such as antioxidant,anti-inflammatory,antibacterial,antivirus,antitumor,etc.,but its low water solubility,low lipid solubility and poor chemical stability resulted in the low bioavailability of curcumin,thus greatly limits the application of curcumin in the field of food and drug.The physiological activity of curcumin requires sufficient curcumin intake and absorption by small intestinal epithelial cells to be effective.Therefore,it is one of the important ways to improve the bioavailability of curcumin by applying the appropriate delivery system to improve the loading level and stability of curcumin.High internal phase emulsions（HIPEs）are those whose volume fraction of the internal phase（dispersed phase）exceeds the close packing limit（approximately 74%）,and they often appear to be semi-solid.Due to its special properties,this kind of emulsion is increasingly used in food,medical,materials and cosmetics.According to the different continuous phase,it can be divided into oil-in-water（O/W）and water-in-oil（W/O）high internal phase emulsions.HIPEs with higher internal phase ratio were selected to achieve high loading of curcumin.Among them,the internal phase of W/O HIPEs can replaced by appropriate solvents（natural deep eutectic solvents（NDES）were selected to dissolve and protect curcumin）,thus the high load and protection of curcumin can be realized.In this paper,polysaccharide-based O/W HIPEs with controllable microstructure and gel strength were constructed.The polysaccharide-based O/W HIPEs loaded with curcumin can be applied to water-soluble food system such as fruit juice,beverage,soft candy,etc.In addition,W/O HIPEs based on natural deep eutectic solvent were also constructed,which can achieve high load and protection of curcumin,and can be applied to oil-soluble food systems such as chocolate,butter,salad dressing,etc.By constructing these two HIPEs,the high load of curcumin and the wide application of curcumin in water-based and oil-based foods can be realized.The formation mechanism and stability of the two emulsion systems as well as the loading,protection and absorption of curcumin from gastrointestinal tract in vitro were investigated.The main results were as follows:A simple approach of homogeneous dispersion was developed to formulate polysaccharide-based HIPEs using complexes of sugar beet pectin（SBP）,tannic acid（TA）,and chitosan（CS）to stabilize the system.The ability of pectin to stabilize the HIPEs was significantly improved after it formed complexes with TA,which were held together by hydrogen bonding.The stability of the HIPEs was further improved by adding CS,which was attributed to the formation of a 3D biopolymer network around and between the oil droplets.The impact of TA concentration,CS concentration,and p H on the oil droplet size,microstructure,and rheology of the HIPEs was investigated.Compared with SBP/TA complexes,the SBP/TA/CS complexes facilitated the formation of stable HIPEs with a gel-like texture and good stability to centrifugation,dilution,thermal treatment,and ultraviolet light.HIPEs prepared from SBP/TA/CS complexes were shown to delay lipid digestion and improve curcumin bioaccessibility.Crystallization W/O HIPEs were prepared by natural deep eutectic solvent（NDES）instead of traditional aqueous solution as internal water phase.The composition of NDES is glucose,sucrose and water,in which the molar ratio of sugar to water is 1:5,and the molar ratio of glucose to sucrose is 5:1～1:5（select 5:1,3:1,1:1,1:3 and 1:5 for investigation）.The interaction to form NDES may be hydrogen bond.The ratio of 1:1,1:3 and 1:5 can be used to obtain stable NDES-HIPEs_w/o.These three proportional emulsions had excellent thermal stability,centrifugal stability,storage stability and freeze-thaw stability,and the emulsions containing crystals had better stability.NDES-HIPEs_w/ocan protect curcumin from UV degradation,and the emulsions containing crystals had better protection effect on curcumin than the emulsions without crystals.In vitro digestion experiments showed that the stability of curcumin in the NDES-HIPEs_w/owas more than twice that of the pure oil group,and the concentration of curcumin in micelles was 1.3-1.5 times that of the pure oil group.Curcumin in crystalline emulsions had better gastrointestinal stability,while curcumin content in the micelles of simulated digestive juices was higher in the HIPEs with lower crystallinity than those with higher crystallinity.In this study,the NDES-based HIPE_W/Ocould be used as a new carrier to improve the in vitro digestion stability and bioaccessibility of curcumin.In addition,the carrier can load high content of curcumin（curcumin in internal phase is 40 mg/g）,which is about11 times of the content of curcumin dissolved in corn oil and about 4 times of that in coconut oil.This study has guiding significance for the construction of water-soluble/oil-soluble HIPEs and the efficient loading and industrial application of curcumin.