Stabilization Of Soybean Oil Body And Soybean Oil Body-Carrageenan Emulsions

As the already existing natural ingredients, soybean oil bodies, with their uniquestructural proteins, oleosins, have gained wide concern because of their potential applicationin foods, cosmetics and pharmaceuticals. This study investigated the flavour and functionalproperties of soybean protein isolate and soy oil-body associated proteins, the stability ofsoybean oil body-carrageenan emulsions under the various environments, the in vitroassessment of the bioaccessibility of fatty acids and tocopherol from soybean oil bodyemulsions stabilized with ι-carrageenan, and the mechanism of the interaction betweensoybean oil body droplets and carrageenan molecules. These results will provide theoreticsupports for the exploitation and preparation of food products of soybean oilbody-carrageenan, the effective bioaccessibility of nutritional materials, and the application ofsoybean oil body associated proteins in the food industry. Main results are as follows:Flavor volatiles profiles and some functional properties of soy protein products producedby five different extraction methods were studied. A method, consisting of ethanol washingand a hydrothermal cooking treatment, was proposed to produce a soy protein product(EWHT). Flavor volatiles profiles, emulsifying ability and whiteness of EWHT wereimproved in comparison with those of acid precipitated soy protein product (AP), soy proteinproduct with oil-body associated proteins and polar lipids removed (OBA/PL-less), soyprotein product obtained from countercurrent extraction (CE) and oil-body associated proteinproduct with polar lipids (OBA/PL). The solubility of EWHT was similar to that of AP,OBA/PL-less and CE, higher than OBA/PL. Therefore the process for preparing EWHT canbe an ideal processing method to produce soy protein with good quality relative to flavor andfunctionality.The physicochemical properties of soybean oil body emulsions for the industryapplication were investigated. Oil bodies were extracted from soybean using an aqueousextraction method and could be used in food. The influence of pH (2-8), NaCl (0-250mmol/L), and thermal processing (30-90°C,30min) on the properties and stability of the oilbodies was analyzed using Zeta-potential, mean particle diameters, and creaming stabilitymeasurements. The rheology properties of soybean oil body emulsions were also determined. The Zeta-potential of soybean oil body emulsions went from around+20mV to－40mV asthe pH was increased from2to8, with an isoelectric point around pH4.5. The soybean oilbody emulsions were stable to aggregation and creaming at low (pH3) and high (pH6)pH values, with the mean particle diameters of around400nm, but were unstable atintermediate values (3<pH <5), which was attributed to their relatively low Zeta-potential.The soybean oil body emulsions were were unstable at higher values (NaCl>25mmol/L, pH7) as a result of electrostatic screening effects. The soybean oil body emulsions were stable tothermal processing from30to90°C (0mmol/L NaCl, pH7.0). The soybean oil bodyemulsion exhibited weak gel-like behavior, and samples were increasingly sheared thinningwith increasing oil content. These results showed that soybean oil body emulsions were stableunder some environmental conditions.The influence of κ, ι, λ-carrageenan on the stability of soybean oil body emulsions atdifferent pH values (pH3,4,5and7) was investigated by particle electrical charge, particlesize distribution, creaming stability and confocal laser scanning microscopy measurements. Inacidic environment (pH3,4and5), the droplet charge of soybean oil body emulsionsstabilized with carrageenan decreased with increasing carrageenan concentration for all typesof carrageenan investigated, suggesting their adsorption to the oil body droplet surfaces.Extensive droplet aggregation and creaming were observed in the emulsions stabilized withλ-carrageenan at pH3and5, indicating that soybean oil body droplets were bridged bycarrageenan. At pH7, there was no significant change in the droplet charge of soybean oilbody emulsions stabilized with three types of carrageenan, but the emulsions stabilized withι-carrageenan were more stable to creaming due to depletion flocculation than the emulsionsstabilized with κ or λ-carrageenan after seven days storage. The probable reason was thatι-carrageenan, which had the most densely charged helical structure, was most effective atcreating highly charged interfacial membranes, thus reducing the depletion flocculation tooccur.The influence of NaCl addition (0-500mmol/L), thermal processing (30,60,90and120°C,30min), and freeze-thaw cycling (－20°C,24h/30°C,2h) on the stability ofuncoated and ι-carrageenan coated soybean oil body emulsions at pH3and7was analyzedusing particle electrical charge, particle size distribution, creaming stability and confocal laser scanning microscopy measurements. For NaCl, the uncoated emulsions were relatively stablefrom0to150mmol/L at pH3, but aggregated at50mmol/L at pH7, which was attributedto electrostatic screening effects; however, the ι-carrageenan coated emulsions at pH3and7were stable at all NaCl concentrations. Both uncoated and ι-carrageenan coated emulsionswere stable at pH7, whereas the uncoated emulsions at pH3became unstable when heatedabove90°C, but the ι-carrageenan coated emulsion droplets at pH3only extensivelycoalesced at120°C, these may be relative to pH and holding temperature. The ι-carrageenancoated emulsions at pH3and7exhibited little droplet aggregation after three freeze-thawcycles in the presence of sucrose. These results suggest that ι-carrageenan coated soybean oilbody emulsions have similar or improved stability compared to uncoated emulsions and maybe utilized as functional soy products in the food and other industries.The in vitro bioaccessibility of fatty acids and tocopherol from natural soybean oil bodyemulsions stabilized with different concentrations of ι-carrageenan was studied. Severalphysicochemical parameters including proteolysis of the interfacial layer, interfacialcomposition and microstructure were evaluated with regard to their impact on thebioaccessibility of fatty acids and tocopherol. Results from simulated human digestion in vitroindicated that the bioaccessibility of total fatty acids and tocopherol decreased (62.7-8.3%and59.7-19.4%, respectively) with the increasing concentration of ι-carrageenan. These resultssuggested that soybean oil body emulsions stabilized with ι-carrageenan could provide naturalemulsions in food which were digested at a relatively slow rate, the important physiologicalconsequence of which might be increasing satiety.