(Epagri - Itajaí Experimental Station) in Santa Catarina, Brazil. Part of the samples was parboiled and the other part had only the hulls removed. Analysis.
CORRELATION BETWEEN PHENOLIC COMPOUNDS AND ANTIOXIDANT ACTIVITY IN BROWN RICE BEFORE AND AFTER PARBOILING Fabiana Kawassaki 1 , Isabel Louro Massaretto1, Rosa Maria Cerdeira Barros 1 , José Alberto Noldin2, Ursula Maria Lanfer Marquez 1 1
University of São Paulo, Faculty of Pharmaceutical Sciences, Department of Food and Experimental Nutrition, São Paulo, Brazil 2 Itajai Experiment Station/Epagri, Santa Catarina, Brazil
Introduction Bioactive components of brown rice, including phenolic compounds, have been investigated because of their potential role in prevention of oxidative stress-related diseases 1. These substances are known for their antioxidant capacity1,2,3. Parboiling process brings technological improvement to the consumer, on the other hand, the effect of this process on bioactive compounds levels is still unknown 4.
Objective To investigate the effect of parboiling brown rice on the phenolic contents and their correlation with antioxidant capacity.
Materials and Methods Twenty seven non-pigmented brown rice (Oryza sativa L.) samples were grown in 2007/2008 by different producers and provided by the Institute of Agronomy (Epagri - Itajaí Experimental Station) in Santa Catarina, Brazil. Part of the samples was parboiled and the other part had only the hulls removed. Analysis were carried out in triplicate according to Figure 1. Rice flour (2 g)
RESIDUAL (Insoluble fraction)
Extraction with EtOH 80% (2 x 10 mL and 1 x 5 mL)
Extraction with hexane (1 x10 mL)
Centrifugation 7000 x g / 10 min
Hydrolysis with NaOH 4M for 4 hours, N2 flow, room temperature Addition of HCl to pH 1 Extraction with ethyl acetate (5 x 30 mL)
SUPERNATANT (Soluble fraction)
Figure 2 - Average contents of soluble and insoluble phenolic compounds and antioxidant activity in samples of brown and parboiled rice (n=27).
Drying in rotary evaporator Up the volume until 25 mL with 80% EtOH
Resuspension in 10 ml EtOH with 80%
Analysis of antioxidant activity by ORAC method
Analysis of antioxidant activity by DPPH method
There is a positive and significative correlation between phenolic compounds and antioxidant activity, with the largest contribution came from the soluble fraction. Insoluble phenolics, in turn, showed a weak correlation with the antioxidant activity (Table 1). This behavior can be explained partly by different types of phenolic compounds present in each fraction. Table 1 – Correlation between total, soluble and insoluble phenolics compounds and antioxidant activity measured by ORAC and DPPH methods.
Analysis of phenolic compounds by FolinCiocalteau method5 Figure 1 – Flowchart of the extraction, quantification and analysis of soluble and insoluble phenolic compounds and antioxidant activity.
Results and Discussion Parboiling decreased in almost 60% the contents of soluble phenolics which were the most affected by the process (Figure 2). However, the insoluble phenolic fraction showed in average a slight increase after rice parboiling, probably due to polymerization and complexation reactions. The same behavior was observed in antioxidant capacity.
Soluble phenolics
Insoluble phenolics
ORAC
0,825*
0,366**
DPPH
0,855*
0,547*
*Significant at p
