Preharvest UVA-LED Enhancing Growth and Antioxidant Properties of Chinese Cabbage Microgreens: A Comparative Study of Single Versus Fractionated Irradiation Patterns

Ultraviolet-A light-emitting diode (UVA-LED) irradiation is an emerging technology for biofortifying plants with enhanced nutraceuticals. This study firstly investigated effects of various doses (0-control, 16, 32, 48 J/cm²) on Chinese cabbage microgreens (CCM) quality, identifying 32 J/cm² as the suitable dose for improving total antioxidant capacity (TAC) of CCM. Based on this dosage, the following two irradiation patterns were compared: single irradiation (SI, single pulse of 32 J/cm²) and fractionated irradiation (FI; four pulses of 8 J/cm² each). Both FI and SI significantly enhanced CCM quality, though through distinct mechanisms. FI effectively promoted accumulation of biomass and vitamin C, with increases by 9.25% and 13.20%, respectively. Meanwhile, SI markedly enhanced 20.90% higher TAC than FI. This was achieved by elevating enzymatic (7.71% superoxide dismutase-SOD, 9.03% peroxidase-POD, 40% catalase-CAT, and 52.17% ascorbate peroxidase-APX) and non-enzymatic (18.89% total phenolics-TPC, 10.04% total flavonoids-TF, and 18.99% carotenoids) antioxidants. Additionally, both FI and SI significantly reduced the nitrate content. To our knowledge, this is the first study to demonstrate the effect of UVA-LED irradiation pattern on microgreens quality. These findings provide basic information for UVA-LED application in indoor agriculture and the food industry, emphasizing the importance of strategically selecting irradiation patterns to achieve specific production goals.