Interfacial Adsorption, Emulsigying And Delivery Properties Of Soy Lipophilic Protein

Other than the storage protein glycinin and β-conglycinin, soy lipophilic protein (LP) isthe third principle fraction (content of31%) in commercial soy protein isolate, which is richin OBBP and soy phospholipids and presents as an amorphous aggregates in aqueous phase.Studies have shown that LP has a good physiological function. Due to their poor solubilityand diffusivity, few researches take notes on their functionality such as interfacial andemulsifying properties. This thesis has evaluated the functionality of LP systematically,including its interfacial adsorption, emulsifying properties and as a delivery device.Furthermore, a concept of “complex interface” composited with hydrophobic protein andsmall molecular weight surfactant was proposed based on the above studies. The main resultsinclude following.1. This thesis find that a nanoparticle can be formed by simple ultrasonic treatment, whichhad an excellent diffusion capacity, improved functionality and be potential to be used in foodindustry. LP can be transformed into a sphere particle with a size of136±0.8nm and surfacecharge of-20.0±0.3mV by ultrasonic treatment. Though the surface hydrophobicity analysisand treated with phospholipase, the structure of the particle was confirmed which wasaggregates of the hydrophobic protein with phospholipids covered on the surface. LP particlewas able to diffuse to the interface and form a complex layer composited with thehydrophobic protein aggregates and phospholipids. The rigid interface was so stable that itwas resistant to be displaced by the small molecular surfactant Tween20. Interfacial rheologytechnology was used to investigate the effects of phospholipase and protease on the interfacialrheology behavior of LP particle, which found that there existed synergic effects between thephospholipids and the hydrophobic protein particles. The synergic effects also be beneficialfor the stability of emulsions which had an excellent physical stability even at long-termstorage (8weeks), heating-salting treatment (90℃/200mM NaCl) and the competitivedisplacement of SMW surfactant (4wt.%Tween20).2. To evaluate the effects of composition of the complex on its stability, soy oil body wasdegreased by organic solvent and then used to form a recombiant oil body. Three differentorganic solvent (acetone, n-hexane, chloroform/methanol) was used to degrease the soy oilbody to control the ratio between OBBP and phospholipids on the surface of recombiant oilbody. Results showed that high content of phospholipids could improve the adsorption of theOBBP on oil-water interface and obtained a high surface pressure and dilatational module. The physical and oxidant stability of recombinant soy oil body formed by the complex ofOBBP and phospholipids was improved by the increasing of phospholipids content.3. Based on the above studies, a concept of “complex interface” composited withhydrophobic protein and small molecular weight surfactant was proposed and comfirmed.Zein and sodium stearate (SS) were used to simulate the natural complex interface. The geltrapping technology (GTT) was applied to observe the morphology and interfacial contactangle of zein particles on oil-water interface. Results showed that SS controlled the adsorptionof zein on oil-water interface. At a low content of SS (2.5mM), the amount of zein adsorptedon interface was low and they presented as regular spherical particles, their contact angle wasfar less than90°. When at a higher content of SS, the particially unfolded zein particleaccumulated on the interface formed a condensed packed layer, their contact angle wasassumed to be closed to or slightly higher than90°according to the SEM. The complex ofzein and SS could be used to form a stable food grade Pickering emulsion, and such stableemulsion could be further freeze-dried to form a structured fat without the usage of trans-orsaturated fatty acids.4. The possibility of LP nanoparticle act as a novel delivery vehicle with hight loadingcapacity for the hydrophobic bioactives was explored. LP nanoparticles as a delivery devicefor the hydrophobic bioactives can load conjugated linoleic acids (CLA) successfully byultrasonic induced assembly, and the loading capacity of this system are as high as26.3±0.4wt.%. The CLA-loaded particle has a size of170±0.63nm. Infrared spectrum and X-raydiffraction were used to confirm the entrapment of CLA in the particles. The oxidationstability of CLA was evaluated by the headspace oxygen consumption and peroxide value.Results showed that CLA loaded in soy lipophilic protein nanoparticles have improvedoxidation stability than it loaded in sodium caseinate micelle or in ethanol. Moreover, theCLA loaded in soy lipophilic protein particles had resistant release characteristics whensubjected to the simulated gastrointestinal digestion.5. The thesis had developed a concept of “double-functional colloidal particle” which couldact as interfacial stabilizer and antioxidants simultaneously. A double-functional nanoparticlecould be formed by entrapping the VEin LP nanoparticles via ultrasonic induced co-assembly.Algae oil emulsions stabilized by this double-functional nanoparticles could form an oil gel(structured fat) when subjected to freeze-drying. Laser scan confocal microscope was appliedto characterize the internal structure of this oil gels. It could be observed that a3-D networkwas formed by soy lipophilic protein nanoparticles and the oil droplets entrapped in thisnetwork separately. Oscillating rheology analysis showed that the formed oil gel in this research had an apparent solid characteristic, and its rheology properties were tunableaccording the concentration of nanoparticles in emulsions. Due to the enrichment ofanti-oxidants on the interface, the algae oil in the double functional particles formed oil gelwas performed to have improved oxidation stability as compared to the case that VEin oilphase or fluid algae oil.