Submitted to: The 1890 Association of Research Directors Biennial Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 12/9/2012
Publication Date: 4/7/2013
Citation: Min, B., Chen, M. 2013. Effect of hydrothermal processing on antioxidant contents and capacities in pigmented rice (Oryza sativa L.). The 1890 Association of Research Directors Biennial Research Symposium. Page 244: Abstract No. 550. Interpretive Summary:
Technical Abstract: Purple and red bran rice cultivars (Oryza sativa L.) are rich sources of antioxidants including lipophilic antioxidants (vitamin E homologues and '-oryzanol), soluble phenolics (including anthocyanidins and proanthocyanidins), and cell-wall-bound phenolics. This study investigated impacts of hydrothermal processing on antioxidant contents and capacities (DPPH radical-scavenging, oxygen radical absorbance, and iron-chelating capacity) in purple, red, and common light-brown bran rice. Rice cultivars were subjected to hydrothermal processing as follows: rough (with hull) and brown (without hull) rice samples were parboiled and, subsequently, wet-cooked. Non-parboiled brown rice was also wet-cooked. Raw (non-hydrothermal processed) purple and red bran rice had 4- to 20-fold higher soluble phenolics and antioxidant capacities compared to raw light-brown rice. Parboiling increased lipophilic antioxidant contents in all cultivars. However, parboiling decreased soluble phenolic contents (especially the heat-sensitive anthocyanins and proanthocyanidins in purple and red bran rice, respectively), leading to reductions in antioxidant capacities. Yet, hydrothermal-processed pigmented rice contained more phenolics and antioxidant capacities compared to hydrothermal-processed light-brown rice. Parboiled brown rice showed greater reductions in soluble phenolics than parboiled rough rice, suggesting the hulls offer protection against thermal degradation and/or leaching of soluble phenolics. Wet-cooking further decreased soluble phenolic contents and antioxidant capacities. Parboiling and wet-cooking appeared to cause increases in the extractability and/or release of bound phenolics. These results suggest that parboiled and wet-cooked brown rice can be an excellent dietary source of lipophilic antioxidants and parboiling rough rice was preferable over parboiling brown rice for preserving soluble antioxidants.