Caryatin and 3'-O-methylcaryatin contents in edible yams (Dioscorea spp.)

The genus Dioscorea hosts a large number of yam species used medicinally and as a staple food by millions of people in tropical countries. All yams share a high antioxidant activity that correlates with their total phenolics contents. However, knowledge of edible species antioxidant phenolics remains incomplete. Bioassay-guided fractionation of the tubers of a yam species with high total phenolics content, D. nummularia, led to the isolation of two flavonols, caryatin and 3′-O-methyl caryatin, contributing over 92% of a stable methanol extract of the tuber in this species. Their structures were determined by high resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR) and a synthesized authentic sample. They displayed no bacterial toxicity. Their content was estimated in the tubers and bulbils of 411 landraces and hybrids belonging to eight food yam species using high performance-thin layer chromatography (HP-TLC). These were found to be highly variable at the intra- and interspecific levels to reach up to 1 030 and 457 μg/g DW respectively and added up to contents of already described antioxidant phenolics. This study provides additional understanding of the health benefits of a yam diet and constitutes the first phytochemical analysis of D. nummularia