Phytosterol and Polyphenol Contents and Quinoa Leave Yields Variation in Relationships to Variety, Density and Harvesting Date

Abstract

Quinoa is an Andean grain known for its gluten-free grains, which are used as a functional food. The aim of this research was to study the possibility of introducing quinoa as a vegetable crop grown for young leaves as a source of polyphenols and phytosterols. To achieve this goal, a field experiment was performed with three quinoa cultivars (Titicaca, Puno, and Vikinga) grown in a split plot design. The experimental factors included three densities (160, 320, and 760 plants·m−2) and two harvest dates (52 and 62 days after sowing (DAS)). The content of phytosterols (ergosterol, stigmasterol, β-sitosterol and campesterol) and polyphenols (ferulic acid, isoquercitrin and rutozid) in quinoa leaves were determined by HPLC method. The phytosterol content varied within the limits: ergosterol 0–7.62 µg·100 g−1 dw, stigmasterol 79.9–175.3 µg·100 g−1 dw, β-sitosterol 425.7–623.1 µg·100 g−1 dw and campesterol 0–5.25 µg·100 g−1 dw. Ferulic acid varied greatly from 38.0 to 63.3 µg·g−1 dw, isoquercitrin ranged from 63 to 101.6 µg·g−1 dw and rutozid varied widely from 32.9 to 162.8 µg·g−1 dw. The total phytosterols and the total phenolic compounds decreased with decreasing plant number density and DAS. This research demonstrated that young quinoa leaves are a good source of phytosterols and phenolics for human consumption.