Structural Investigation of Oat Protein Isolate in Aqueous Medium by using Synchrotron Small-angle X-ray Scattering

Oat protein isolate (OPI) is among the plant proteins with valuable functionalities (e.g. emulsification) during daily supplement intake. Understanding their structures helps to manipulate oat proteins at small scale, which enables the appropriate deployment of their functions. Based upon such understanding, the molecular structure of oat protein isolate (OPI) in aqueous medium was investigated by synchrotron small-angle X-ray scattering (SAXS), and this study allows a structural reconstitution of OPI in aqueous medium. Besides, this SAXS study is complimentary to the previous study (Liu et al. J. Agric. Food Chem. 2009, 57, 4552-4558)1. From form factor fitting, we confirmed that OPI aqueous solutions at low concentrations (0.3~2 mg/mL) obtained a disk conformation (41.4x41.4x10.2 [A]3). Once protein concentration increased to 5 mg/mL and 10 mg/mL, the individual disk proteins formed large-dimensional rodlike aggregates, which was evidenced by the analyses of effective structure factor and pair distribution function (PDF). Based on the PDF results, the ab initio models of OPI particles at low concentrations (0.3 mg/mL to 2.0 mg/mL) were restored by using GASBOR algorithm. Finally, we found that weak attraction between OPI particles occurred, which was verified by second virial coefficient and pair potential.