Fabrication And Bioavailability Of Quercetin-Food Emulsion Systems

Quercetin is the major source of flavonoid in the typical human diet,has been shown to exhibit a range of beneficial physiological activities,and plays an important role in preventing chronic diseases and improving human health.However,quercetin has a low bioavailability and limited application in food,which is associated with its poor water solubility,low absorption and rapid metabolism.Emulsion is the most common food product,and has been widely used as a food delivery system to encapsulate,deliver and protect nutrients,nutraceuticals,flavors,etc.There is yet no consensus has been reached about the impact of composition,structure,interface and texture properties of food emulsions on the bioavailability of nutrients or nutraceuticals.Therefore,the present study fabricated surfactant-and protein-stabilized quercetin-excipient emulsion systems,food particle-stabilized quercetin-multiple emulsion systems and quercetin-Pickering emulsion systems with various interface compositions to investigate the impact of emulsion composition,structure,interfacial composition and texture on release property,digestibility,bioaccessibility and physiological activity of emulsions.The major findings of the present study are shown as follows:(1)Surfactant-and protein-stabilized quercetin-excipient emulsion systems were fabricated.The components(oil content and emulsifier type)and texture(viscoelasticity,gel strength and structure)of excipient emulsions had a major effect on the digestibility,bioaccessibility and physiological activity of their components.Tween-80-stabilized excipient emulsions significantly enhanced the solubility of quercetin,the highest solubility of quercetin in emulsions was 430 μg/mL.Bioaccessibility and in vivo antioxidant activity of quercetin in emulsions were improved markedly,as the increase of corn oil level in the emulsion from 4%to 10%,the solubility and antioxidant activity of quercetin was further increased.Proteins may be efficient natural alternatives of Tween-80 for stabilization of excipient emulsions.Soy protein isolate,whey protein isolate and sodium caseinate can bind to quercetin through hydrophobic interactions to form complexes,the numbers of quercetin-binding sites in the three proteins were all around 1.Sodium caseinate can bind to relatively more quercetin molecules to form the highest stable complexes,and sodium caseinate-stabilized emulsions were most effective in increasing the solubility,stability and bioaccessibility of quercetin.The potential of excipient emulsions stabilized with different emulsifiers for improving quercetin bioaccessibility decreased in the following order:sodium caseinate-stabilized emulsions(76%)>whey protein isolate-stabilized emulsions(56%)≈ Tween-80 stable emulsion(60%)>soy protein isolate-stabilized emulsions(24%).Liquid emulsions and emulsion gels with different texture properties were derived from sodium caseinate-stabilized emulsions.The viscoelasticity of liquid emulsions had little impact on protein and lipid digestion and quercetin bioaccessibility(～51%).Compared to liquid emulsions,the surface area of emulsion gels exposed to the digestive enzymes was reduced during the digestion process,thereby inhibiting protein and lipid digestion,and reducing quercetin bioaccessibility.With the increase of gellan gum level in the emulsion gels from 0%to 0.2%,the gel structures became more compact,proteolysis and lipolysis were gradually inhibited,and quercetin bioaccessibility was reduced from 46%to 33%.(2)Food particle-stabilized quercetin-multiple emulsion systems were fabricated.The gliadin nanoparticles had a moderate affinity for both oil and the water phase,but were more affinitive to water phase,thereby making the oil-water interface bend toward the oil phase to form emulsions.In order to achieve long-term stability of W/O/W emulsions,the matrix(gelatin,sucrose)of internal water phase and the microenvironment(pH)of external water phase were regulated to gelatinize both internal and external water phase,and balance the osmotic pressure balance.These W/O/W emulsion gels were employed for co-encapsulation of hydrophilic EGCG and hydrophobic quercetin,the encapsulation efficiency was 65.5%and 97.2%,respectively.W/O/W emulsion gels can control the release of internal EGCG and quercetin,and contribute to a 2-and 4-fold increase in the bioaccessibility of EGCG and quercetin.Compared to W/O emulsion,W/O/W emulsion gels can further increase the bioaccessibility of EGCG,while both types of emulsions contributed to similar bioaccessibility of quercetin.(3)Quercetin-Pickering emulsion systems with various interface compositions were fabricated.Both gliadin nanoparticles and gliadin-phospholipid hybrid nanoparticles can reduce the oil-water interface tension,thereby reducing the energy barrier of particle adsorption,then promoting the adsorption of the particles at the oil-water interface to form emulsions.These nanoparticles were observed to adsorb on the droplet surface to form O/W Pickering emulsions with a mean particle size of 708-1146 nm,which were stable against gravity-induced phase separation.The interfacial particle composition of Pickering emulsions had a major effect on the encapsulation,release and bioaccessibility of quercetin.As the increase of the interfacial phospholipid level(0-70%),both the interfacial dilational elasticity and encapsulation efficiency of emulsions were gradually increased.These Pickering emulsions were quite efficient to control quercetin release,and a higher interfacial phospholipid level led to a faster release rate of quercetin.The presence of phospholipid in interfacial particles reduced the rate and extent of lipid hydrolysis,but with the increase of interfacial phospholipid level(0～70%)of Pickering emulsions,quercetin bioaccessibility was increased from 17%to 34%.