The Impact of Supplementary Short-Term Red LED Lighting on the Antioxidant Properties of Microgreens

Microgreens are a very specific type of vegetables and are considered to be in the group of "functional foods" which are products that process particular health promoting or disease preventing properties that are additional to their normal nutritional value. The aim of this study was to evaluate the impact of supplementary short-term red LEDs lighting on the antioxidant properties of microgreens. Different species of red and green leaf microgreens (amaranth, basil, mustard, spinach, broccoli, borage, beet, kale, parsley, pea) were grown to harvest time in a greenhouse in a peat substrate under daylight with supplementary lighting provided by standard high-pressure sodium lamps (HPS). At pre-harvest stage of 3 days, HPS lamps were supplemented by 638 nm LEDs, whereas reference plants continued staying under lighting conditions identical to those of growth. PPFD generated by illuminator was 170 mu mol m(-2) s(-1) and net PPFD generated by the illuminator in combination with HPS lamps - 300 mu mol m(-2) s(-1) (16-h; 19-22/15-18 degrees C). Due to the increased activity of the metabolic system for the protection from a mild photooxidative stress antioxidant properties of microgreens were changed. Natural antioxidant compounds were in order: pea>broccoli>borage>mustard=amaranth>basil=kale>beet=parsley>tatsoi. Total phenols concentration increased with supplemental red in all microgreens from 9.1% in mustard to 40.8% in tatsoi, except of amaranth, where decrease of 14.8% was observed. Ascorbic acid content increased in amaranth (79.5%), pea (65.2%), kale (60.6%), broccoli (59.1%) and mustard (25.0%), but decreased in basil (53.9%) and borage (46.9%), and had no significant effect in tatsoi, beet and parsley. Total anthocyanins significant increased in broccoli (45.1%), kale (44.0%), amaranth (38.0%), tatsoi (34.5%), parsley (27.0%) and pea (14.6%), significant decrease was detected in borage (51.8%), mustard (45.1%) and beet (43.3%) and was not significantly affected in basil.