Design Of Whey Protein Isolate-sodium Alginate Emulsion Delivery Systems And Their Stabilization Mechanism Of Lycopene

In recent years,the nutritional and health effects of food have received wide attention from people.Lycopene is a fat-soluble pigment belonging to the carotenoid family and is most abundant in tomato tissues.Lycopene has a variety of physiological functions such as anti-oxidation,immune regulation,anti-cancer,etc.However,lycopene has poor water solubility,low stability,easy degradation in gastrointestinal tract,resulting in low bioavailability,which limits its application in functional foods and health care products.The stability and bioavailability of lycopene can be improved by different delivery systems.Firstly,in this thesis,the interface of tomato juice system was modified based on the principle of emulsion design,aiming at the lycopene in fresh tomato,and the regulation effect of edible oil,emulsifiers and texture improver on the stability and bio-accessibility of lycopene in fresh tomato was studied.Secondly,on the basis of emulsion system,the different emulsion gel systems were then established to entrapment and deliver purified lycopene.The formation mechanism of the emulsion gel was systematically explored.Finally,the ability of emulsion gel to promote lycopene uptake by intestinal epithelial cells was demonstrated by in vitro digestion and cell models.The main research contents and results are as follows:(1)Mechanism of enhancing the stability and bio-accessibility of lycopene in tomato pulp by emulsion system:Different types and different concentrations(0-8 wt%)of edible oils(olive oil or corn oil),emulsifiers(Whey protein isolate,WPI)or texture modifier(Sodium alginate,SA)were added into tomato pulp the principles of emulsion design,and the physical and chemical properties of the composite system were studied by homogenization.The addition of these substances enhanced free lycopene release from tomato tissue.During homogenization,the addition of WPI resulted in the formation of smaller oil droplets and stronger light scattering,which led to the turbid tomato pulp.The addition of SA increased the viscosity of tomato pulp,thus increasing its uniformity.Adding8 wt%corn oil and 1 wt%WPI into tomato pulp,lycopene exhibited the best storage stability.With 6 wt%olive oil and 1 wt%SA as additives,the bio-accessibility of lycopene was the best(61.5%).(2)Formation mechanism and physicochemical properties of WPI emulsion gel:Based on the emulsion template method,a combination of high energy homogenization and cold gelation was used,the emulsion gel of WPI was prepared by cross-linking agents-induced method,and its microstructure,rheological properties and processing properties were evaluated.Transglutaminase(TG)induced cross-linking of the gels to form emulsion gels containing small aggregates,while Ca²⁺induced cross-linking of the gels to form larger aggregates.The apparent viscosity,strength,water-holding capacity,and hardness of the emulsion gel were all increased after the double crosslinking.The above results showed that TG and Ca²⁺had synergistic effect on the emulsion gel which induced the cross-linked three-dimensional space structure.(3)Construction and functional properties of WPI-SA composite-based emulsion and emulsion gel:Design different interface structures(layer-by-layer assemble emulsion and complex emulsion)and induce emulsion cross-linking through TG and Ca²⁺to form emulsion gel.The results of circular dichroism,SDS-PAGE,microscopic images and rheological behavior confirmed that WPI pre-heat treatment exposed hydrophobic residues to form protein aggregate particles,and then mixed with polysaccharides to form emulsion gels with small pores.Furthermore,cross-linking makes the gel strength and viscosity greater,while the hydrophobic residues of heating the WPI-SA composite were not fully exposed after heating,resulting in a slightly weaker gel strength,and Ca²⁺induced cross-linking was the dominant role,but the water holding capacity was higher.The above results indicate that the layer-by-layer emulsion has better gel properties under the same conditions.(4)In vitro digestion and intestinal absorption of lycopene in WPI-SA composite emulsion gel:The temperature accelerated test and in vitro digestion model were established to study the effects of WPI-SA composite emulsion gel on the storage stability and gastrointestinal stability of lycopene.The results showed that the double cross-linking emulsion gel significantly improved the storage stability and digestion stability of lycopene compared with free lycopene.The results of MTT toxicity test showed that the emulsion gel had no cytotoxicity to Caco-2 cells.Lycopene loaded composite emulsion gel exhibited stronger anti-inflammatory activity on cells;the results of lycopene content in cells showed that the absorption of lycopene in Caco-2 cells was promoted by WPI-SA emulsion gel.To sum up,the physical stability and bio-accessibility of lycopene in tomato products can be improved by emulsion design principles.Based on emulsion template method,WPI emulsion gel with excellent rheological properties and excellent functional properties was successfully constructed by TG and Ca²⁺double crosslinking.In addition,WPI-SA composite emulsion gel was used to entrapment lycopene,which enhanced the release of lycopene.The stability of the gastrointestinal tract and the absorption rate of lycopene in intestinal epithelial cells provide a new way to improve the application value of lycopene.