Effects of bran pigmentation and parboiling on rheological properties of waxy rice in neutral and acidic environments

Background and ObjectivesPigmented rice is a good source of polyphenols that can interact with proteins to affect starch rheological properties. Parboiling influences rice functional properties via starch gelatinization and protein denaturation, but its effects on polyphenol/protein/starch interactions are unknown. This study investigated the rheological properties of pigmented (HB-1) and nonpigmented (Neches) waxy rice in neutral (water) and acidic (0.1 N HCl) environments as affected by soaking at room temperature or 5 degrees C below onset gelatinization temperature (T-o) and steaming. FindingsWhole grain rice and starch of both varieties shared similar pasting viscosities, whereas milled HB-1 displayed a higher peak viscosity than its derived starch. Soaking at 5 degrees C<T-o increased pasting viscosities of whole grain and milled Neches and whole grain HB-1, but decreased those of milled HB-1. Parboiled whole grain and milled HB-1 after high-temperature soaking showed lower storage (G') and loss (G") modulus in neutral environment, but enhanced viscoelastic properties in acidic environment. ConclusionThe results provide evidence for the presence of inherent polyphenol/protein/starch interactions in pigmented rice. These interactions may be enhanced from protein denaturation during parboiling but disrupted when exposed to acid to increase starch swelling. Significance and NoveltyPolyphenol/protein/starch interactions may help develop functional foods with increased viscosity in acidic environment.