Highly stable aq. soy protein (SP) colloids have been facilely prepared by high-speed blending (30k rpm, 15 min) to homogeneously disperse up to 97.7 % of soy protein isolate at up to 9 %. Aq. SP colloids were amphoteric with a 4.5 isoelectric point and ζ-potentials ranging from +32.4 mV at pH 2.2 to-39.1 mV at pH 7.1 with respective average hydrodynamic diameters of 157 and 233 nm. Diluted aq. SP colloids (0.0001 %) dried on hydrophilic mica appeared as 6.0 nm thick and 16.4 nm wide disk-like nanoparticulates. Aq. SP colloids were also amphiphilic, reducing water surface tension to 41.2 mN/m at > 0.98 % and could be solvent-exchanged to dimethyl formaldehyde or 4:1 v/v methanol/water. Colloidal SPs exhibited preferential affinity and adhesion to cellulose filter paper to significantly improve the respective tensile modulus and strength by 70 and 42 % at merely 2.8 % dried add-on. The improved cohesion of 6.2 % SPs was evident by drying at 110°C to further increase the respective tensile modulus and strength of cellulose by another 78 and 41 %.
Amphiphilic protein microfibrils have been generated for the first time by ice-templated self-assembly of aqueous globular protein colloids and subsequent selective disassembly in polar solvents like MeOH, EtOH, acetone, and dimethylformamide. Semicrystalline microfibrils, ca. 1.2 μm wide and 45−70 μm long, produced from soy proteins are excellent amphiphiles, which are capable of stabilizing both high-internalphase o/w and w 1 /o/w 2 double emulsions as well as retaining amphiphilicity even with surface-bound lipophiles and electrophiles. This ice-templated self-assembling and polar solvent disassembling approach is applicable to other legume proteins, such as pea proteins, and is scalable to process globular proteins into amphiphilic microfibrils for Pickering emulsions in many potential applications including food, pharmaceuticals and skin care.
Uniquely amphoteric soy protein (SP)-rich ultra-fine fibers (231 nm average diameter) have been facilely electrospun from aq. colloids and rendered water-insoluble by heating (150 °C, 12 h) to be highly stable over 14 d (pH 7) as well as under extremely acidic to basic (pH 0−10, 2 d) or at boil (2 h) conditions. The SP-rich fibrous membranes are easily tuned to be charged either negatively by deprotonation above or positively by protonation below the 4.5 PI of SPs. This pH-responsive amphoterism has been demonstrated for rapid adsorption of either cationic or anionic dyes, selective adsorption of either dye from their mixtures, and repetitive adsorption/desorption to recover and reuse both dyes and membranes. Chemisorption and heterogeneous adsorption of ionic dyes was confirmed by close fitting to the pseudo-second-order kinetic model (R 2 = 0.9977−0.9999) and Freundlich adsorption isotherm (R 2 = 0.9879). This is the first report of water-resilient and pH-robust ultrafine fibrous membranes fabricated from aqueous colloids of neat globular SPs, the major byproducts of under-utilized edible oil and biodiesel. The natural polyampholyte origin, amphoterism, and green processing make these fibrous materials unique and versatile for many potential applications involving both anionic and cationic species.
2D structures from amphiphilic and amphoteric protein microfibrils with tunable surface amphiphilicity, pH-responsive controlled release of cationic and anionic species.
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