Location: Grain Quality and Structure ResearchTitle: Wheat bran particle size influence on phytochemical extractability and antioxidant properties Author
Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2013
Publication Date: 1/1/2014
Citation: Brewer, L.R., Kubola, J., Siriamornpun, S., Herald, T.J. and Shi, Y. 2014. Wheat bran particle size influence on phytochemical extractability and antioxidant properties. Food Chemistry. 152:483-490. Interpretive Summary: Phytochemicals including carotenoids phenolic acids, flavonoids, and anthocyanins present in wheat bran offer health promoting benefits. Phytochemicals offer natural antioxidant benefits to help reduce diseases such as cancer. This research was designed to determine whether or not the particle size of the wheat bran after milling had any impact on the amount of these valuable health compounds extracted. The particle size of three different milled treatments (coarse, medium and fine whole wheat bran) was measured and the health promoting compounds determined. The results indicated that smaller particle size improved the extraction of phytochemicals and increased the oxygen radical absorbance capacity.
Technical Abstract: It is unknown if particle size plays a role in extracting health promoting compounds in wheat bran because the extraction of antioxidant and phenolic compounds with particle size reduction has not been well documented. In this study, unmilled whole bran (coarse treatment) was compared to whole bran milled to medium and fine treatments from the same wheat bran. Antioxidant properties (capacity, ability, power), carotenoids and phenolic compounds (phenolic acids, flavonoids, anthocyanins) were measured and compared. The ability of whole bran fractions of differing particle size distributions to inhibit free radicals was assessed using four in vitro models, namely, diphenylpicrylhydrazyl radical-scavenging activity, ferric reducing/antioxidant power (FRAP) assay, oxygen radical absorbance capacity (ORAC), and total antioxidant capacity. Significant differences in phytochemical concentrations and antioxidant properties were observed between whole bran fractions of reduced particle size distribution for some assays. The coarse treatment exhibited significantly higher antioxidant properties compared to the fine treatment; except for the ORAC value, in which coarse was significantly lower. For soluble and bound extractions, the coarse treatment was comparatively higher in total antioxidant capacity (426.72 mg ascorbic acid eq./g) and FRAP value (53.04 µmol FeSO4/g) than bran milled to the finer treatment (314.55 ascorbic acid eq./g and 40.84 µmol FeSO4/g, respectively). Likewise, the fine treatment was higher in phenolic acid (7.36 mg FAE/g), flavonoid (206.74 µg catechin/g), anthocyanin (63.0 µg/g), and carotenoid contents (beta carotene, 14.25 µg/100g; zeaxanthin, 35.21 µg/100g; lutein 174.59 µg/100g) as compared to the coarse treatment. An increase of surface area to mass increased the ORAC value by over 80%. With reduction in particle size, there was a significant increase in extracted anthocyanins, carotenoids and ORAC value. Particle size does effect the extraction of phytochemicals.