Seasonal variation of ascorbic acid and nitrate levels in selected basil (Ocimum basilicum L.) varieties

Abstract

The aim of this study was to determine the levels of ascorbic acid and total nitrates in the fresh aerial parts of different varieties of basil (Ocimum basilicum L.) in different growing seasons. The ascorbate-nitrate index (I<sub>AN</sub>) is used to determine the safety of basil for consumers. Seven basil varieties (‘Ohře’, ‘Lettuce Leaf’, ‘Purple Opaal’, ‘Dark Green’, ‘Mammolo Genovese’, ‘Mánes’ and ‘Red Rubin’) were cultivated as pot cultures in greenhouses during the period 2015–2016. High-performance liquid chromatography (HPLC) was used to determine the ascorbic acid content, which ranged from 34.3 to 222.0 mg/kg f. w. An ion-selective electrode was employed to determine the content of nitrates, which ranged from 237.7 to 4280.6 mg/kg f. w. The ascorbate-nitrate index reached values of between 0.016 and 0.629, which are risky-to-moderately safe ascorbate-nitrate ratios. However, the occasional use of small amounts of basil as a culinary herb is not risky for consumers. Furthermore, significant differences in the content of ascorbic acid and nitrates were found among the cultivated samples with respect to variety, year and growing season.