Evaluation of morphology, nutrients, phytochemistry and pigments suggests the optimum harvest date for high-quality quinoa leafy vegetable

Consumed as a leafy vegetable, quinoa has high value for its unique nutritional and functional composition; however, optimal harvesting time is unknown. Leafy green quinoa was evaluated for morphological traits, nutritional content, phytochemical composition and pigments at eight different harvesting dates. Harvesting time had a significant influence on morphological traits. Leafy green quinoa picked at 55 days after sowing (DAS) was highest with thickest stem, largest leaf number and leaf area, and heaviest leaf yield. Nutritional composition—reducing sugar, crude fat, ash, minerals, and amino acids—varied with harvesting time. Fat content decreased as the harvest date was delayed, quinoa vegetable harvesting at 25 DAS had highest contents of K, Ca, acidic amino acids (AAA), and neutral amino acids (NAA), while harvesting at 45 DAS had highest contents of ash and Ca. Phytochemical composition—total flavonoids (TF), total phenolics (TP), and total saponin (TS) content—were different among harvesting time. Maximum contents of β-carotene, lycopene, chlorophyll a and chlorophyll b were harvested at 25 DAS. Principal component analysis (PCA) and relationship analysis showed that late harvest (50-55 DAS) was beneficial for yield formation of quinoa vegetables with higher plant, thicker stem, more leaf numbers, larger leaf area and higher leaf yield as well as higher contents of TP, TS and Mg. Earlier medium harvest (25-35 DAS) was suggested to harvest quinoa vegetables with higher contents of AAA, BAA, HAA, NAA, K, β-carotene, lycopene, and reducing sugar. For the purpose of ash and Ca, later medium harvest (40-45 DAS) was recommended. To pursue higher contents of chlorophyll a, chlorophyll b, TS, fat and Cu, earliest harvest (20 DAS) was recommended. Overall, 25 DAS might be considered the best time for harvesting high-quality leafy green quinoa for commercial purposes.