THE EFFECT OF UV-A SUPPLEMENTAL LIGHTING ON ANTIOXIDANT PROPERTIES OF OCIMUM BASILICUM L. MICROGREENS IN GREENHOUSE

Abstract

The effects of supplemental UV-A LED lighting on growth and antioxidant properties of two varieties of basil (Ocimum basilicum L.) microgreens were determined. Purple-leaf ‘Dark Opal’ and green-leaf ‘Sweet Genovese’ basils were grown in greenhouse (14 days, 22/18 ± 2 °C day/night temperature, 40 ± 5 % a relative air humidity) during winter season. The main lighting system (HPS lamps and natural daylight) was supplemented with ~13.0 μmol m-2 s-1 flux of UV-A 390 nm, and a total PPFD was ~125 μmol m-2 s-1 (16 h photoperiod) for 1 or 7 days before harvest, or entire growth period – 14 days. The results revealed that the influence of UV-A on growth and antioxidant properties depended on basil variety and duration of irradiation. Generally, UV-A irradiation for 7 days significantly (P ≤ 0.05) inhibited growth and hypocotyl elongation of green-leaf basils, and for 14 days of both basil varieties. No significant differences on leaf chlorophyll index were determined. However, leaf flavonol index significantly increased in green-leaf basils after 7 and 14 days UV-A irradiation. The total phenols ant anthocyanin contents significantly decreased after 1 day UV-A irradiation in purple-leaf basils, and the continuous decrease following UV-A irradiation for 7 or 14 days was determined. In addition, UV-A irradiation had negative effects on ABTS radical activity in purple-leaf basils; however, the significantly higher ABTS radical scavenging activity after UV-A irradiation for 1 or 7 days in green-leaf basils were determined. UV-A influenced higher ascorbic acid synthesis in purple-leaf basils after 7 days irradiation, or after 14 days irradiation in both basil varieties. In summary, the supplemental UV-A LED lighting allows to protect basil microgreens from hypocotyl elongation, and enhances antioxidant properties in green-leaf basils. Purple-leaf basils showed to be more sensitive to UV-A irradiation, and less positive effects on antioxidant properties were determined.