The Emulsion Properties And The Relationship Of Structure-function Of Legumes Protein

Many plant protein show excellent emulsifying properties, however there are fewknowledge about emulsifying mechanism of legumes protein, and also lack of scientificcognition to the relationship of its structure and function. In this thesis, Physiochemical andemulsifying functional properties of pea protein was studied. Stability mechanism of emulsionsstabilized by PPI was explored in pH3.0. Finally in order to unravel the important role ofconformational flexibility at the quaternary levels in the emulsifying and interfacial propertiesof phaseolin, an ideal vicilin (or7S globulin) from red kidney bean. The results were as follows:All the three pea proteins (protein isolate, vicilin and legumin) exhibited poorestemulsifying ability at pH5.0(close to the isoelectric point of the proteins), and concomitantly,the resultant emulsions were most unstable against coalescence and creaming. The emulsifyingability of these proteins at pH3.0was better than that at neutral or alkali pH values, and amongall the three proteins, pea legumin (PL) exhibited highest emulsifying ability at this pH. Theemulsion stability against flocculation, coalescence and even creaming also to a variable extentdepended on the type of the proteins and the applied pH.The PL and pea vicilin (PV) exhibitedmuch better creaming stability than PPI, at pH deviating from the pI. The emulsifyingproperties of these proteins were not only related to their PS and H0, but also associated with theprotein adsorption and the nature (e.g., viscoelasticity) of interfacial protein films.At pH3.0, most of the proteins in PPI were present in the nanoparticle form, with thehydrodynamic diameter of134~165nm depending on the concentration (c;0.25to3.0%). Forthe emulsions formed at a specific oil fraction of0.2and varying c values of0.25-3.0%,increasing the c resulted in a considerable reduction in the emulsion size, while their creamingstability progressively increased, and especially at c values higher than2.0%, no creamingoccurred even after storage of20days. And at higher c values, a gel-like network could beformed. The emulsions formed at c values above1.0%exhibited extraordinary stability againstcoalescence. The gel-like network formation was closely associated with the increased amountof adsorbed proteins at the interface. The results suggest that pea proteins exhibit a goodpotential to act as a kind of Pickering-like stabilizers for oil-in-water emulsions at acidic pH.The conformational flexibility at quaternary and tertiary levels of phaseolin wasmodulated by urea with increasing concentrations from0to8M, an ideal vicilin (or7S globulin)from red kidney bean. With this method, the effects of quaternary conformation on theemulsifying and interfacial properties of vicilin was symmetrically studied. At c=0.5%, the presence of increasing concentrations (0-8M) of urea resulted in a progressive disassociation oftrimeric phaseolin molecules into monomeric ones. One point is noteworthy to be strengthenedthat the urea-induced structural unfolding of phaseolin at quaternary and/or tertiary levels iscompletely reversible. This suggests that the urea dissociated and denatured phaseolin subunitsin the solution are present in the state more like the “molten globule state”. Increasing the ureaconcentration progressively improved the emulsifying ability of the protein, and flocculatedextent of oil droplets in the fresh emulsions, but led to a progressive decrease in interfacialprotein concentration.On the other hand, the adsorption experiments showed that theimprovement of the emulsifying ability was highly dependent on ease of structuralrearrangement of the adsorbed proteins. These observations clearly confirmed that theflexibility of phaseolin at quaternary and/or tertiary levels plays a vital role in its emulsifyingability, mainly through the way of affecting the ease of structural rearrangement of adsorbedproteins at the interface.In general, it was confirmed that emulsifying property of soy protein is influenced byvarious factors (e.g. pH, concentration of protein and protein structure). It is of greatimportance for related research to understand emulsifying properties of legumes protein andrelated molecular mechanism in-depth, and it is also has a certain reference value to explore theapplication of legumes protein.