The self-assembly/aggregation of zein in ethanol-water solutions of high solids mass fraction was studied by ultra-small-angle x-ray scattering (USAXS). Ethanol content of solutions was 70-90% (v/v), zein concentration 30-60% (w/v), and oleic acid 0 or 14% (w/w zein). USAXS analysis revealed that depending on ethanol content and protein concentration three or four structures of different sizes may coexist in zein solutions. Structures in the high q region exhibited a rod shape with radius of gyration (Rg) below 50 Å. Intermediate structures were found in the range of 300 – 900 Å, where corresponding Porod slope (P values) of ~3 suggested an irregular shape. In the low q region, the unified fit model predicted P=4 for structures of Rg, 3,000 – 6,000 Å indicating the presence of larger spherical structures with smooth surfaces. The absence of mass fractals suggested that zein structures were formed through self-assembly, rather than by clustering of primary particles. The addition of oleic acid notably affected the size and shape of structures formed in zein solutions. The impact of oleic acid on the smallest structures (Rg &lt; 30 Å) was seen in their disk-like shape, different from corresponding structures in zein only solutions. At low q vectors, the size of aggregated/self-assembled oleic acid-zein structures was much larger than those in zein only solutions. Larger Rg values suggested oleic acid facilitated the assembly process, perhaps playing a surfactant role. P values suggested oleic acid promoted an earlier structure development by forming discs and spheres faster than samples without it. According to our results, self-assembly of zein develops various structures in concentrated solutions. Oleic acid facilitates the assembly process.

Ultra-small-angle x-ray scattering study of zein self-assembly

251st National Meeting (2016)

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