Enhancement of accumulation of bioactive compounds in red leaf lettuce by manipulation of UV light before harvest

Abstract

In a plant factory with artificial light, accumulation of bioactive compounds can be enhanced via precise environmental control. Light is essential for growth and development, and for the production of bioactive compounds in plants. Ultraviolet (UV) light stimulates bioactive compound biosynthesis in plants including antioxidants. We developed a new and economical UV-rich fluorescent lamp (UV-FL), with the ability to adjust the ratio of UV-A and UV-B. The objective of this study was to determine the effect of UV light on the accumulation of bioactive compounds in red leaf lettuce. Red leaf lettuce plants were grown in a plant factory with normal growing conditions under white light as light source (23/20°C, 70% RH, 16 h light period, PPFD 150 μmol m-2 s-1, 1,000 ppm CO2) for 23 days. The plants were subjected to UV light under white light (low, middle, and high; 0.3, 0.6, and 0.9 W m-2) for 3 days before harvest. Fresh and dry weights of shoot, leaf area, total chlorophyll, total phenolic concentration, and ORAC for antioxidant activity were measured before and after the UV treatments. Middle and high UV treatments resulted in negative effects on the growth characteristics such as shoot fresh and dry weight, and leaf area. However, low UV treatment was not significantly different from the control for shoot dry weight. Total chlorophyll was higher in low and middle UV treatments than the high UV treatment and the control. In contrast, total phenolic concentration and ORAC value of lettuce plants grown under UV treatments were significantly higher than that of the control. This study suggests that short-term UV irradiation using economical UV-FL lamp before harvest was effective in improving the vegetable quality. ? 2020 International Society for Horticultural Science. All rights reserved.