LED illumination affects bioactive compounds in romaine baby leaf lettuce.

Background: The effect of light quality on phytochemicals in romaine baby leaf lettuce 'Thumper' was investigated in (I) a closed environment and (II, III) a greenhouse (16 h, 21/17 °C): (I) basal (638, 455, 660, 735 nm) LEDs supplemented with UV (380 nm), green (510 nm), yellow (595 nm) or orange (622 nm) LEDs (PPFD of ∼175 µmol m(-2) s(-1) ); (II) high-pressure sodium (HPS) lamps (90 µmol m(-2) s(-1) ) supplemented with blue (455, 470nm) or green (505, 530nm) LEDs (30 µmol m(-2) s(-1) ); (III) at 3 days before harvesting, HPS lamps (90 µmol m(-2) s(-1) ) supplemented with red (638 nm) LEDs (210 µmol m(-2) s(-1) ).

Results: (I) Supplemental UV or orange light enhanced phenolic compounds, supplemental UV or green light enhanced α-carotene, and supplemental green light enhanced anthocyanins. All supplemental LED colours had a negative effect on tocopherol and ascorbic acid levels. (II) HPS lighting supplemented with different LEDs was not efficient, since the increase in some compounds did not compensate the decrease in major tested phytochemicals. (III) Short-term irradiation with supplemental 638 nm LEDs before harvesting in the greenhouse did not have a significant effect on phytochemical contents, apart from enhancing tocopherols.

Conclusion: Wavelength control using LED technology affects the production of secondary metabolites, as the metabolism of many nutrients is light-dependent. The narrow-bandwidth supplemental light effects were diminished by broader-spectrum HPS light or natural daylight in the greenhouse.