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

Authors: JANNASCH, ANNEGRET - University Of Arkansas; WANG, YA-JANE - University Of Arkansas; LEE, SUN-OK - University Of Arkansas; McClung, Anna; BROWNMILLER, CINDI - University Of Arkansas

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2023
Publication Date: 5/23/2023
Citation: Jannasch, A., Wang, Y., Lee, S., McClung, A.M., Brownmiller, C.R. 2023. Effects of bran pigmentation and parboiling on rheological properties of waxy rice in neutral and acidic environments. Cereal Chemistry. https://doi.org/10.1002/cche.10678.
DOI: https://doi.org/10.1002/cche.10678

Interpretive Summary: There is increasing interest in developing enhanced nutritional food products and because of the increase in global diabetes and obesity, there has been concern in how to keep rice as part of a healthy diet. Although most commercialized rice has a brown bran layer, there are rice varieties with purple and red brans. Research has shown that relative to brown rice these pigmented brans are rich in natural antioxidant compounds that have been linked with health beneficial effects. These pigmented rices are being marketed directly but little research has been conducted on the impact of processing methods like parboiling on these pigmented compounds and their subsequent rheological properties in cooked rice. In addition, most commercial rice has 15-25 percent amylose content, a starch component that affects cooked rice texture and processing quality. However, waxy rice varieties have essentially 0 percent amylose causing the cooked rice to have an extremely viscous texture and a slower gut digestion resulting in greater satiety. This research was conducted to explore the combination of pigmented bran and parboiling on viscosity of waxy rice with the goal of developing a food product that is nutritionally rich and satisfying. Brown bran and purple bran waxy rices were compared for starch viscosity properties after using two parboiling treatments. One set of treatments resulted in increased viscosity likely due to crosslinking between the polyphenols and proteins in the pigmented bran and, when exposed to an acidic environment like the stomach, was observed to have increased starch swelling. These findings indicate protein-polyphenol interactions of pigmented rice may help develop functional foods with improved rheological properties for enhanced satiety that may reduce dietary caloric intake.

Technical Abstract: Pigmented rice is a good source of polyphenols that have been shown to interact with proteins to affect starch rheological properties. Parboiling influences rice functional properties via starch gelatinization and protein denaturation, but its effects on protein-polyphenol interactions are unknown. This study investigated the rheological properties of pigmented (HB-1) and non-pigmented (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. Brown rice and starch of the rice varieties Neches and HB-1 shared similar pasting viscosities, whereas milled HB-1 displayed a higher peak viscosity than its derived starch. Soaking at 5°C