Histochemical and biochemical analysis of major aroma compound (2-acetyl-1-pyrroline) in basmati and other scented rice (Oryza sativa L.)

Abstract

Histochemical studies were carried out to localize the major aroma compound 2-acetyl-1-pyrroline (2AP) in mature rice caryopsis of basmati and other scented rice varieties. Among the histochemical reactions tried, the reagent 2,4-dinitrophenyl hydrazine was found to localize 2AP. The structure of 2AP includes a nonreactive pyrroline ring and a reactive methyl ketone group, which reacts with 2,4-dinitrophenyl hydrazine to produce an orange-red coloured compound, 2-acetyl-phenyl hydrazone. The reaction was confirmed in Pandanus amaryllifolius leaves, which is known to contain ten times higher concentration of 2AP than basmati rice, and also with the extracts of P. amaryllifolius in paper chromatogram. The biochemical analysis revealed that among the cultivars studied, the marketed basmati rice showed maximum 2AP content (0.061 ppm). Pusa basmati grown during the rainy season had 0.030 ppm 2AP followed by the local scented cultivar Ghansal (0.028 ppm). The non-scented variety Krishnahansa and Pusa basmati rice grown during summer do not show any presence of 2AP. This study may help in better understanding the biology of rice grain and improvement of rice quality.