Identification of the Major Odorants in Fresh Rhizomes and Leaves of the Chinese Culinary Herb Houttuynia cordata

Abstract

Houttuynia cordata is an essential culinary herb in Asian countries and belongs to the Saururaceae family. Its edible rhizomes and leaves are accompanied by a distinctive fishy aroma, contributing to its popularity as a foodstuff. However, the molecular background of its characteristic aroma is still unclear. To fill this gap, we isolated the volatile compounds of freshly harvested rhizomes and leaves by solvent extraction and automated solvent-assisted flavor evaporation and screened them for odor-active compounds by applying a comparative aroma extract dilution analysis. For the structural assignment, the odor properties, retention indices, and mass spectra of the Houttuynia cordata odorants were compared with data obtained from authentic reference compounds. This approach resulted in the identification of 44 and 41 odorants in fresh rhizomes and leaves, respectively. FD factors ranged up to 16384 for the rhizomes and up to 4096 for the leaves. The odorant with the highest FD factors in both samples was identified as metallic, soapy, and fishy smelling 3-oxododecanal. The presence of 3-oxododecanal in Houttuynia cordata has already been reported, but its potential contribution to the plant's characteristic odor has not yet been considered. Toward clarifying the tautomeric composition of 3-oxododecanal, quantum calculations suggested a predominance of the enol forms in the plant. Future experiments will be focused on unequivocally identifying the key odorants in fresh Houttuynia cordata rhizomes and leaves and confirming the assumption that 3-oxododecanal plays a major role in the overall aroma.