Qualitative Analysis by High-Performance Thin-Layer Chromatography–Bioautography of Ecuadorian Chenopodium quinoa Willd. Leaves: Influence of Variety, Phenological Stage, and Place of Cultivation on Free Radical Scavenging and α-Amylase Activity

The present study aimed to qualitatively assess the influence of Chenopodium quinoa Willd. varieties (INIAP-Tunkahuan, INIAP-Pata de Venado varieties and Chimborazo genotype), phenological stages (40, 60, and 80 days), and places of cultivation (Pichincha and Chimborazo Ecuadorian provinces) on the leaf and seed phenolic composition and biological properties. Their nutraceutical potential was assessed through qualitative analyses of (i) their polyphenols by high-performance thin-layer chromatography (HPTLC); and (ii) their free radical scavenging (quenching of 2,2-diphenyl-1-picrylhydrazyl free radical, DPPH•) and α-amylase inhibitory properties (iodine visualization of starch hydrolysis) by HPTLC–bioautography. Compared to seeds, the quinoa leaf methanolic extracts present a high content of polyphenols with free radical scavenging activity, and compounds with an α-amylase inhibitory property; both biological activities indicate a remarkable potential of quinoa leaves, which may be relevant for the treatment of diabetes but also for the chemoprevention and/or treatment of pathologies related to oxidative stress. In quinoa leaves harvested after 80 days of cultivation, regardless of the place of production and the variety, a high content of bioactive compounds was observed. Future research is undoubtedly needed to further promote quinoa leaves as a dietary vegetable or to develop them into a nutritional supplement. This would empower quinoa smallholders in Andean regions to promote the sustainable development of this culture in its places of origin.