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

Abstract

AbstractBackground 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°C below onset gelatinization temperature (To) 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°C<To 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.