Impact of Harvesting Time on the Levels of Nitrate and Flavonoids in Spinach

Health promoting compounds present in leafy vegetables are beneficial to maintain optimum health. Spinach (Spinacia Oleracea), a green leafy vegetable, is a rich source with health promoting compounds such as nitrate, flavonoids, carotenoid, ascorbic acid and vitamins but their composition varies with different harvesting time. Flavonoids reported to exhibit anti-viral, anti-cancer, anti-inflammatory, and anti-allergic activities. Nitrates maintain cardiovascular health and increasing muscle efficiency. In the current study, the levels of nitrate and flavonoids were measured in spinach at different growing time in the season was investigated. Spinach samples were different (20, 30, 40, 50 and 60 days) harvested period. Nitrate and flavonoids were extracted with water and methanol respectively and analyzed by reversed phase high performance liquid chromatography (HPLC) and compounds were separated on C₁₈ column. Results demonstrated that the harvesting time had a significant effect on the nitrate levels increasing from day 20 days (954 µg g^-1) to 40 days (1833 µg g^-1) and then decreased (487 µg g^-1) at 60 days. A total 12 different flavonoids were identified in spinach by HPLC-high resolution mass spectra by positive and negative mode. The concentration of flavonoids varied among the sample collected at different harvesting time. For example 5,3 ,4 -Trihydroxy-3-methoxy-6:7-methylendioxyflavone-4-β-D-glucuronide is the major flavonoid in spinach among other flavonoids. Spinach harvested at an early stage (between 20 to 30 days) has higher levels of nitrate and flavonoids as compared to spinach harvested at later. It is clear from present study; the harvesting period has major impact to consider in determining the levels of health promoting compounds.