Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 27, 2012
Publication Date: February 27, 2013
Citation: Chen, M., Min, B., Mcclung, A.M. 2013. Effect of hydrothermal processes on antioxidants and their capacities in whole grain rice (Oryza sativa L.). 34th Rice Technical Working Group Meeting Proceedings. February 27-March 1, 2012 Hot Springs, Arkansas. p.176. Technical Abstract: The impacts of parboiling and wet-cooking alone or in combination on concentrations of lipophilic antioxidants (vitamin E homologs and '-oryzanol), soluble phenolics (including proanthocyanidins and anthocyanins), and antioxidant capacities (DPPH radical scavenging capacity (DPPH), oxygen radical absorbance capacity (ORAC), and iron-chelating capacity (ICC)) in whole grain rice from 6 rice cultivars of different color were investigated. The six rice cultivars were selected on the basis of their bran colors: one white, light brown, brown, and red, and two purple. The color of whole grain rice is classified on the basis of the descriptions for rice bran color in the on-line database of the Germplasm Resources Information Network. The hydrothermal processes included parboiling of rough (PR) and brown rice (PB) for comparison with non-parboiled brown rice (raw control). Brown rice that was produced following these treatments and the control were then wet-cooked using 1 rice : 2 water ratio in a rice cooker. Analysis of samples following PR and PB, with or without wet-cooking, demonstrated increased concentrations of lipophilic antioxidants in all rice cultivars as compared to the raw control and the wet-cooked brown rice. Parboiling of rough and brown rice decreased concentrations of phenolics, DPPH, ORAC, and ICC in the soluble fraction of most rice cultivars, and their decreases were more prominent in red rice cultivars. Furthermore, parboiling of brown rice led to more extreme decreases than parboiling of rough rice suggesting protection by the hulls against thermal degradation or leaching of water-soluble antioxidants. Wet-cooking of parboiled rice (PR and PB) caused greater decreases compared to wet-cooking of raw brown rice. In conclusion, the parboiling process increased concentration of extractable lipophilic antioxidants, and parboiling rough rice was preferable to parboiling brown rice to preserve soluble antioxidants. At every step of the thermal processes, with the losses due to thermal degradation and leaching, dark bran whole grain remained several-fold higher in water-soluble antioxidant concentrations and capacities than light bran whole grain rice.