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

Authors: JANNASCH, ANNEGRET - University Of Arkansas; WANG, YA-JANE - University Of Arkansas; LEE, SUN-OK - University Of Arkansas; LIYANG, ROHANNA - University Of Arkansas; MCCLUNG, ANNA - Retired ARS Employee

Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Varieties of rice with pigmented bran have emerged as potential nutraceutical and functional food ingredients with health-promoting benefits due to the presence of different classes of polyphenols in the bran. Long-term consumption of polyphenols may offer preventive and therapeutic effects for cardiovascular disease, cancer, neurodegenerative diseases, type-2 diabetes, osteoporosis, and obesity. In addition, rice protein has high digestibility, biological availability, and hypoallergenicity, indicating it is an ideal functional ingredient in food and beverage products. Glutelin represents the predominant protein fraction in both brown and milled rice. The concentration and type of polyphenol and protein molecules present in the grain can affect their structural and nutritional properties. This study explored how the polyphenols in purple and red bran rice may affect the functional and nutritional properties of rice glutelin. Milled, whole grain, and rice bran of brown, red, and purple bran varieties were evaluated for changes in protein structure. Phenolic acids inherently present in brown bran rice did not alter glutelin structure, whereas high concentrations of anthocyanins and flavan-3-ols/proanthocyanidins in purple bran and red bran rice, respectively, formed intra-molecular covalent bonds with glutelin making the protein more compact. These changes in glutelin structure in pigmented bran rice may improve rheological and nutritional properties and result in novel health beneficial food products using natural ingredients from rice.

Technical Abstract: Pigmented and non-pigmented bran rice contains different polyphenol classes. Covalent bonding of polyphenols with glutelin, the major protein fraction in rice, can occur in pigmented rice. The effect of polyphenol class on glutelin structure and proteomic analysis was studied by SDS-PAGE, HPSEC and LC-MS/MS techniques. Milled rice, whole grain rice and bran from brown (Neches), purple (HB-1) and red (Scarlett) brans mainly comprising phenolic acids, anthocyanins, and flavan-3-ols/proanthocyanidins, respectively, were used. Glutelin in milled rice, regardless of bran color, had similar molecular weight and size and proteomic identification due to a lower abundance of polyphenols. Covalent polyphenol-glutelin bonds, decreased the glutelin identification, whereas phenolic acids caused little or no structural changes in glutelin. In contrast, the presence of anthocyanins and flavan-3-ols/proanthocyanidins in HB-1 and Scarlett, respectively, caused a more compact glutelin structure through intra-molecular bonds in whole grain rice and bran. Polyphenol-protein interactions may be utilized to tailor food ingredients from pigmented rice with desired functionality.