Abstract:

The present study investigated the separation and purification of purple rice protein-polyphenol complexes as
well as their structural composition and molecular morphology. Purple rice protein-polyphenol complexes were separated
from purple rice by Osborne sequential extraction. It was found that the purity of purple rice protein was (94.3 ± 2.7)%,
and the content of polyphenol was (10.1 ± 4.0) mg/g. Sodium dodecyl sulfate polyacrylamide gel electrophoresis results
indicated that purple rice protein-polyphenol complexes were significantly different from rice glutenin in terms of subunits
with molecular weight over 37 ku. The amino acid composition of protein-polyphenol complexes was richer than that of
rice glutenin as analyzed by post-column derivatization with ortho phthalaldehyde, with superiority observed in essential
amino acid composition according to the FAO/WHO model. The monomeric anthocyanins in purple rice protein-polyphenol
complexes, identified by high performance liquid chromatography with diode array detector-mass spectrum, was cynidin-
3-O-glucoside and paeonidin-3-O-glucoside. Atomic force microscope showed that the surface topography of purple rice
protein-polyphenol complexes was irregularly spherical with particle size of 4.7 nm. This study can provide the scientific
basis for further studies on functional and biological characteristics of colored rice.

Key words: purple rice, protein-polyphenol complexes, structural composition, molecular morphology, atomic force microscope