Characterization and discrimination of premium-quality, waxy, and black-pigmented rice based on odor-active compounds

Odor-active compounds have been studied in cooked aromatic rice, but not in specialty rice types that have distinctly different flavors. We analyzed the odor-active compounds emanating from three different types of specialty rice (premium-quality, waxy and black-pigmented) and identified the differences in odor-active compounds among them.

Twenty-one, 21 and 23 odorants were detected using GC-O for cooked samples of premium-quality, waxy and black-pigmented rice cultivars, respectively. Hexanal was the main odorant in premium-quality and waxy cultivars; however, waxy cultivars had 16 times higher hexanal odor activity values (OAVs) than premium-quality cultivars, indicating premium-quality rice had a less pronounced overall aroma. 2-Acetyl-1-pyrroline was the main contributor to overall aroma in black-pigmented rice, followed by guaiacol. The three types of specialty rice were clearly discriminated based on the OAVs of their odor-active compounds using multivariate analyses. Six odor-active compounds [2-acetyl-1-pyrroline, guaiacol, hexanal, (E)-2-nonenal, octanal and heptanal] contributed the most in discriminating the three types of specialty rice. Six very similar superior cultivars of premium rice could likewise be readily separated using aroma chemistry.

The ability to discriminate the aroma among rice types using the OAVs of the principal odor-active compounds facilitates our understanding of the aroma chemistry of specialty rice.