Pakchoi (Brassica rapa subsp. chinensis) is one of the most widely consumed
vegetables
in Asian countries, and it is high in secondary metabolites. The availability,
quantity, and quality of light play a critical role in the growth
and development of plants. In this study, we investigated the effect
of LEDs (light-emitting diodes; white, blue, red, and red + blue)
on anthocyanin, glucosinolates, and phenolic levels in red pakchoi
baby leaves. On the 24th day after sowing (DAS), red baby pakchoi
leaves were harvested, and shoot length, root length, and fresh weight
were measured. Among the different LED treatments, there was no significant
difference in shoot length, whereas the highest root length was achieved
in the red + blue LED treatment (23.8 cm). The fresh weight also showed
a significant difference among the different LED treatments. In total,
12 phenolic and 7 glucosinolate individual compounds were identified
using high-performance liquid chromatography (HPLC) analysis. The
highest total glucosinolate (2937 μg/g dry wt) and phenolic
(1589 μg/g dry wt) contents were achieved in baby leaves exposed
to red + blue light. Similarly, the highest contents of total anthocyanins
(1726 μg/g dry wt), flavonoids (4920 μg/g dry wt), and
phenolics (5900 μg/g dry wt) were achieved in the red + blue
treatment. Plants exposed to red + blue LED light showed the highest
accumulation of anthocyanin, glucosinolates, and phenolic compounds.
For antioxidant activity, DPPH (2,2-diphenyl-1-picrylhydrazylradical)
free radical scavenging, ABTS (2,2-azinobis (3-ethylbenzothiazoline)-6-sulfonic
acid) radical scavenging, and reducing power assays were performed,
and the antioxidant activity of red pakchoi baby leaves grown under
red + blue LED light was found to be the best. The metabolic profiling
of the identified metabolites revealed distinct separation based on
the secondary metabolites. This research will be helpful for farmers
to choose the best LED light combination to increase the secondary
metabolic content in pakchoi plants.