AACC International - 2011 Meeting Abstract - Correlation between phenolic compounds and antioxidant activity in brown rice before and after parboiling

Meeting Abstract - Poster Presentation

Correlation between phenolic compounds and antioxidant activity in brown rice before and after parboiling
F. Kawassaki (1), A. S. Mikaro (1), I. L. Massaretto (1), J. A. Noldin (2), U. M. MARQUEZ (1)
(1) University of São Paulo, Faculty of Pharmaceutical Sciences, São Paulo, Brazil; (2) Agronomic Institute EPAGRI, Itajaí, Brazil
Cereal Foods World 56:A47

Phenolic compounds, from an analytical point of view, can be classified into free, conjugated (soluble), and bound (insoluble) substances. The objective of the study was to investigate the effect of parboiling brown rice on the phenolic contents and their correlation with antioxidant capacity. Twenty-seven nonpigmented brown rice samples were grown in 2008 by different producers and provided by the Institute of Agronomy (Epagri - Itajaí Experiment Station) in Santa Catarina, Brazil, before and after parboiling. Soluble phenolic compounds were extracted with EtOH 80% and bound phenolics were released by NaOH, then extracted with ethyl acetate and analyzed for their phenolic contents. Antioxidant activity was measured by the oxygen radical absorbance capacity (ORAC) and the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging methods. The ratio between soluble and insoluble phenolics in nonparboiled brown rice was 55:45. Parboiling decreased in about 59% the contents of soluble phenolic compounds which were the most affected by the process, while the insoluble phenolic fraction showed in average a slight increase after rice parboiling, probably due to polymerization and complexation reactions. Correlation coefficients between levels of soluble phenolics and antioxidant activity were high and independent on the method used. The coefficients were r² = 0.825 (p < 0.01) for ORAC and r² = 0.855 (p < 0.01) for DPPH. For bound phenolics, coefficients were weak (r² = 0.547 [p < 0.01] and r² = 0.366 [p < 0.01] for DPPH and ORAC, respectively). Although the absolute antioxidant activity, measured by the two methods showed different order of magnitude, correlation coefficients were similar. In conclusion, antioxidant activity is due mainly to soluble phenolics in nonparboiled rice, while in parboiled rice soluble and insoluble fractions contribute almost equally with antioxidant capacity.