Proceedings of the XLVII Italian Society of Agricultural Genetics - SIGA Annual Congress

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 5.35

Red and white rice genotypes have different antioxidant accumulation in the grain

A. gianinetti*, F. Finocchiaro*, B. Ferrari*, G. Galaverna**, N. Ferrari**, N. Pellegrini***

*) Istituto Sperimentale per la Cerealicoltura, sezione di Fiorenzuola

**) Dip. di Chimica Organica e Industriale, Università di Parma

***) Dip. Sanità Pubblica sezione di Igiene, Università di Parma

rice, proanthocyanidins, antioxidant activity

Rice is one of the most consumed cereal in the world. It is employed as polished grain, i.e. deprived of hulls embryo and kernel coats (pericarp fused with seed coats, and aleuronic layer). With red grained rice it is meant a rice, either cultivated or weedy, whose kernel is contradistinguished by a brick-red (reddish brown) colour, visible after removing the husk (floral bracts) which covers the caryopsis. As polishing leaves a few portions of kernel coats, if some red grains from weedy rice were originally present in the batch, the marketed product could show a varying percentage of red striped grains.

The chemical identification of pigments, distinguishing them from standard white-grained rice, is still uncertain. It has been observed that the reddish coloured testa is associated with the presence of a class of polimeric polyphenols (proanthocyanidins) and it has been observed also that red grained rice has a great antioxidant activity and epathoprotective action, due to its high level of antioxidants compounds.

Aim of this research is to establish the antioxidants composition (tocols, polyophenols, oryzanols) and the total antioxidant activity of whole grains in a red variety (S. Eusebio) and in a white rice variety (Loto) cultivated in the same farm. Samples of dehulled rice flour were analysed.

For these purposes, an extraction procedure has been developed, which consists of extraction of the milled rice sample with three different solvents of growing polarity: hexane, acetone/water + 1% HCOOH, methanol/water + 1% HCOOH. The polyphenols characterisation was carried out with RP-HPLC analysis (water/acetonitrile gradient with 0.2% of formic acid or NaCl) equipped with Photo Diode Array detector and mass spectrometer ZMD Micromass with electrospray interface. Polimeric polyphenols were characterised with HPLC-DAD-MS.

The Total Antioxidant Activity (TAA) was measured by the ABTS radical cation assay in all three fractions obtained with the three solvents. It was also evaluated the content of tocols (tocopherol and tocotrienol) and oryzanol in the hexane fraction. The HPLC-DAD-ESI-MS analysis has demonstrated that the red variety has high levels of polimeric polyphenols that belong to proanthocyanidin class. These polymers are completely absent in the white rice. The TAA was measured with the ABTS-flow injection method. The red rice has a very high TAA, if compared with the white variety (almost 5 times higher), primarily due to the high contribution of the acetonic fraction. This fraction contains the proanthocyanidin polimers, which, then, appeared to be the compounds that primarily characterize the red variety analyzed and differentiate it from the white varieties commonly cultivated.

In view of the high levels of proanthocaynidins in this red grained rice and the possible use of this rice variety as a source of dietary antioxidant, it will be interesting to evaluate the presence and the concentration of these compounds also in other cereals with reddish testa. After using red grained rice line as a model matrix, we are currently screening barley germoplasm for red grained genotypes.