Study On Fabrication,Characterization And Potential Applications Of Camellia Oil Bodies Based Structured Systems

Solid fats are essential energy sources for our diet,which can provide desirable palatability,texture,functionality and sensory attributes,as well as contribute to flakiness and tenderness.However,their application in food products is limited because they contain considerable amounts of trans and saturated fatty acid contents which may contribute to diet-related health problems,such as diabetes,obesity and cardiovascular disease.Regulatory authorities and consumers are demanding more natural and healthy foods.Therefore,considering the high demand for healthy ingredients and the transition to more sustainable foods,oil structuring appears to be an outstanding strategy to substitute solid fats,provide food products with a better nutritional profile and transfer active substances.However,currently widely used structured systems based on synthetically engineered oil droplets have some disadvantages,such as low oil binding capacity,poor structure recovery ability,and easy oxidation of vegetable oils.Moreover,the resultant food presents a rough structure and reduced flavor,which is greatly different from the food prepared by traditional solids fat.Therefore,there is a need for designing new structured systems based on plant materials.The objective of this research was to explore the possibility of developing structured systems based on the oil bodies(OBs)derived from camellia seeds.Initially,the composition of OBs,and physicochemical properties of OB emulsions stabilized by biopolymer are given because many plant-derived OBs are designed to simulate their properties.Then,OBs-based oleogels were prepared via an electrostatic layer-by-layer deposition technique that contained OB droplets coated by biopolymers,followed by Schiff base cross-linking using aldehyde-based cross-linkers.The effects of interfacial characteristics and Schiff bases on the formation and properties of OBs-based oleogels were investigated by analyzing microstructure,thermal stability,rheology,texture,protein degradation and lipid digestion.Lastly,the feasibility of OBs-based oleogels as drug delivery systems was explored under simulated gastrointestinal models(gastric and duodenal phases).The research results not only provide theoretical guidance and data support for the construction strategy of OBs-based structured systems and applications in different scenarios,but also have practical significance for the high-value utilization of OBs from camellia seeds.The main contents and results of this article were summarized as follows:(1)The composition of OBs extracted from mature camellia seeds through aqueous media was found to comprise three intrinsic proteins,with molecular weights of 15 k Da and 17 k Da(oleosins)and 30 k Da(caleosin),and three major phospholipids(phosphatidylethanolamine,phosphatidylcholine and phosphatidylinositol).The main fatty acids in the OBs were oleic acid,palmitic acid,linoleic acid,and stearic acid with composition of 80.07%,9.65%,7.11%,and1.79%,respectively.Afterward,physiochemical characteristics of OB emulsions were investigated over a wide range of p H values,ionic strengths,temperatures,and freeze-thaw cycles using gum tragacanth(GT)as a coating layer.The electrostatic GT-OB surface protein interactions were confirmed byζ-potential and CLSM measurements,which resulted in the reduction of flocculation effects and enhancement of steric stabilization due to the adsorption of biopolymer to OB surfaces.When the concentration of GT increased from 0 to 1 wt%,the activation energy values(E_a)appeared in the range of 21.92 to 8.02 k J/mol at p H 4.In addition,the OBs were found to be soft droplets with the degree of structure recovery ranging from 0.451 to 0.533,however,GT coating synergistically increased the recovery of OB structures,suggesting rapid formation of structures due to the reversibility of the electrostatic interactions.(2)Emulsion gels based on OBs were prepared through covalent cross-linking with oxidized polyphenols,including catechin(OCT),caffeic acid(OCF),chlorogenic acid(OCA),and tannic acid(OTA).The structural characteristics,thermal stabilities,antioxidant activities,rheological properties,and lipid digestion kinetics of the resulting cross-linked OB-polyphenol emulsion gels were studied.Analyses of free sulfhydryl and amino group contents,FTIR,fluorescence spectroscopy,and surface hydrophobicity confirmed the formation of C–S or C–N bonds between polyphenols and proteins of OBs.The covalent binding of polyphenols to the OBs resulted in increased denaturation temperature values from 109.87℃ for OBs to 112.61,114.21,118.84,and121.73℃ for OB-OCF,OB-OCT,OB-OCA and OB-OTA emulsion gels,respectively.The OB-based emulsion gels cross-linked by polyphenols exhibited greater scavenging activities for DPPH radicals and ferrous ions.Based on weak gel and structural kinetic models,the OBs-based emulsion gel cross-linked by OTA had the tightest 3-D network and strongest elasticity than those cross-linked by OCA,OCF,and OCT.The cross-linking ability of polyphenols also influenced the lipid digestion kinetics,as evidenced by CLSM analyses,which showed a slower disintegration of the protein matrix under gastric conditions and delayed the release of free fatty acids.(3)This study reports the development of OBs-based oleogels structured using electrostatically coated OBs with chitosan as an outer layer,followed by vanillin induced Schiff base cross-linking of the coated droplets.The study found that the driving forces behind the construction of the oleogels were electrostatic interaction,Schiff base reaction,and hydrogen bond cross-linkages.Morphological analysis demonstrated that chitosan coating on the OBs prevented the oiling-off of oleogels from 47.91%to 9.83%,while vanillin addition fabricated micro-network structures that tightly packed the droplets into 3D-network structures.From differential scanning calorimetry analysis,it was exhibited that 1.5 wt%vanillin added with 1.5 wt%chitosan stabilized gel achieved a good balance between peak temperature and enthalpy of oleogels.Macro-properties showed that the cross-linked oleogels were thermally stable with excellent thixotropic recovery ability(97.6%),as well as,had higher gel strength(G′>18k Pa)and gel hardness(13.10 N)values,suggesting that interfacially adsorbed chitosan and interconnected vanillin networks together contributed to the development of solid oleogel structures.Moreover,lipid digestion kinetics revealed that cross-linking slowed down the free fatty acids release rate of oleogels,which was attributed to the compact coating layer formed by chitosan that partially restricted the interfacial displacement by enzymes and the integrated networks induced by vanillin that reduced the void spaces available for the diffusion of lipases and bile salts.(4)The layer-by-layer deposition technique and Schiff base reaction mechanism were used to create multi-component oleogels based on OBs,κ-carrageenan,chitosan and vanillin.Flowable to self-standing oleogels were obtained by alternating deposition of biopolymer coatings on OB droplets confirmed from macro-micro structure properties.The CLSM and cryo-SEM micrographs showed that the outer surface of the uncoated OBs-based oleogel had holes,cracks,and dents.However,the biopolymers formed well-defined interfacial layers around the OBs,which were able to retain their structural integrity with uniform morphology,and excellent oil holding capacity(>99.7%).Creep-recovery rheology indicated that Schiff base crosslinking of bilayer oleogels increased their elastic deformation restorability from 83.62%to 93.32%due to the generation of stronger,and more rigid network structures with greater cohesive force.The oleogels exhibited excellent thermal stability with high G′(>35 k Pa),yield stress(>1000 Pa),hardness(15.03 N),cohesiveness(0.60),and springiness(0.81)values,indicating the synergistic development of solid structures by compact coating layers and vanillin-induced networks.Furthermore,softer OB oleogel presented a much higher lipolysis rate(48.16%)given the rapid breakdown of their surrounding protein membranes,while more compact oleogel structures,such as those found in bilayer(31.68%)and cross-linked(24.65%)oleogels,significantly delayed the FFA release.Also,CLSM and SDS-PAGE results suggested that,compared to the 15 k Da oleosin and the 30 k Da caleosin of OBs,the 17 k Da oleosin exerted a strong protective effect during gastric process,as it was able to retain a part of undigested oleogels.(5)The OB emulsions encapsulating different curcumin concentrations(0.2 to 1 mg/g)were prepared using a p H-driven method combined with ultrasound treatment,followed by electrostatically driven layer-by-layer deposition of gum arabic and chitosan to form oleogels.The resulting oleogels were further cross-linked using 2,3,4-trihydroxybenzaldehyde(TB)to strengthen the structure of gel.FTIR and TEM analyses indicated that curcumin was incorporated into the hydrophobic domain of OBs,and biopolymers were flatly adsorbed onto the membrane surface of OBs through electrostatic attraction,maintaining intact spherical morphology of droplets.The encapsulation efficiency of curcumin in the OBs increased from 63.47%for uncoated OBs to 83.65%and 92.18%for gum arabic and gum arabic-chitosan coatings,respectively.The gum arabic-chitosan coated oleogels efficiently entrapped the oil(99.07%)and the TB crosslinking resulted in closely packed 3D-network structures with excellent gel strength(>4.8×10~5 Pa),which together found to be effective in protecting the loaded bioactive against UV irradiation and high temperature-induced degradation.Furthermore,the combination of biopolymers and TB synergistically hindered the simulated gastric degradability of oleogels;releasing only 23.35%,12.46%and 7.19%of curcumin by gum arabic,gum arabic-chitosan,gum arabic-chitosan-TB stabilized oleogels,respectively,while it resulted in a sustained and controlled release effect during intestinal phase.