Polyphenol-mediated covalent bonds on glutelin structural changes in rice with different bran colors

Pigmented and non-pigmented rice cultivars contain different polyphenol classes. Covalent bonding of polyphenols with glutelin, the major protein fraction in rice, can occur in pigmented rice. The effects of polyphenol class on glutelin molecular weight and size were studied via SDS-PAGE and HPSEC, respectively. The proteomic analysis of glutelin was performed via LC-MS/MS. Rice cultivars with brown (Neches), purple (HB-1) and red (Scarlett) bran colors mainly comprising phenolic acids, anthocyanins, and flavan-3-ols/proanthocyanidins, respectively, were used. Glutelin in milled rice exhibited similar molecular weight and size and proteomic identification due to the lower concentration of polyphenols. Covalent modification of glutelin by polyphenols decreased the amount of identified glutelin. Phenolic acids caused little or no structural changes of glutelin. Anthocyanins and flavan-3-ols/proanthocyanidins in whole grain rice and bran of HB-1 and Scarlett caused a more compact glutelin structure through intra-molecular bonds. Polyphenol-protein interactions may be utilized to tailor food ingredients from pigmented rice with desired rheological properties.