Effects of LED treatments on the growth and nutritional content of lettuce (Lactuca sativa) in a hydroponic vertical farming system

Introduction: LED-integrated hydroponic vertical farming system (HVFS) may address food security challenges arising from urbanisation, while antioxidants in vegetables may prevent cardiovascular disease. This study aimed to explore the LED effects on yield, antioxidant properties, and vitamin C content in Butterhead lettuce (BL) and Italian lettuce (IL). Methods: Three LED combinations were used: 77% red, 14% green, and 9% blue lights (77R:14G:9B); 7% red, 41% green, and 52% blue lights (7R:41G:52B); and 25% red, 67% green, and 8% blue lights (25R:67G:8B). The concentration and pH of nutrient solution in HVFS ranged from 0.878-2.061ppm and 6.0-6.6, respectively, with a 12:12 light-dark cycle. Chlorophyll and anthocyanin contents were measured using chlorophyll and anthocyanin meters, respectively. Total phenolic and vitamin C content were measured using Folin-Ciocalteu colorimetric assay. Total flavonoid and antioxidant activity were determined through aluminium chloride colorimetric assay and 2,2-diphenyl-1-picrylhydrazyl (DPPH) colorimetric assay, respectively. Completely randomised design was adapted with three replications. Results: BL exhibited greater yield, anthocyanin and chlorophyll contents, while IL had higher vitamin C content. Significantly (p<0.001) higher yields were produced under 77R:14G:9B and 25R:67G:8B. Significantly higher phenolic (p<0.001) and flavonoid (p=0.003) contents were produced under 25R:67G:8B. Vitamin C was significantly (p=0.037) higher under 25R:67G:8B than 7R:41G:52B. Conclusion: LED treatment with higher proportion of red light generated greater yield, whereas higher proportion of green light gave higher phenolic, flavonoids, and vitamin C accumulation. This study provided preliminary data on boosting crop yield and phytochemical contents, which may improve food self-production and population health.