Leafy herbs grown in traditional soil base systems serve as a potential source of secondary metabolites with antioxidant activity^{(Reference Henning, Zhang and Seeram1)}. However, published data on the antioxidant profiles of herbs grown under hydroponic vertical farming systems is extremely limited. The aim of this study was to determine the profiles of antioxidant-relevant metabolites in vertically farmed herbs.

Samples of Italian Basil, Flat Coriander, Flat Parsley, Dill, and Green Mint (n = 10 per crop) were grown in a vertical farming unit, under white light (day night cycle of 18/6 hours). Irrigation was conducted every two hours (during day period) using the Ebb and Flow technique. Plant growing cycle was between 3 weeks plus nursery time; upon harvesting, herbs were freeze-dried overnight. Total Phenolic content (TPC), total carotenoids and chlorophyll, and ascorbic acid/vitamin C were determined in crops using spectrophotometric methods. A welch ANOVA with Games-Howell post hoc test was used to verify inter-crop effects if data were normally distributed, otherwise a Kruskal- Wallis test with post-hoc Dunn test was used if data were not normal (RStudio Version 2022.07.2 + 576). In all cases, significance was achieved when p < 0.05.

Phenolic compounds in Italian Basil (40.04 ± 6.08mg/g DW) showed greater content of these compounds in comparison to Flat Parsley (8.49 ± 1.35mg/g DW), Flat Coriander (7.55 ± 0.58mg/g DW), and Dill (7.13 ± 1.63mg/g DW) (p < 0.01). Dill demonstrated higher content of total carotenoids (1.16 ± 0.13mg/g DW) in comparison to other crops (p < 0.01). Flat Parsley (0.60 ± 0.08mg/g DW) showed higher levels in comparison to Green Mint (0.43 ± 0.11mg/g DW), Italian Basil (0.40 ± 0.06mg/g DW), and Flat Coriander (0.20 ± 0.17mg/g DW) (p < 0.05). Regarding total ascorbic acid, Green Mint (4.19 ± 1.18mg/g DW), Flat Parsley (4.17 ± 0.86mg/g DW) and Flat Coriander (3.58 ± 0.62mg/g DW) showed the highest content; Italian Basil (2.84 ± 0.40mg/g DW) demonstrated reduced concentrations in comparison to Flat Parsley (p < 0.05). Dill (1.89 ± 0.05mg/g DW) showed the lowest values of ascorbic acid in comparison to the other species (p < 0.01).

Nutrition databases indicate that soil-based herbs may generally have higher total phenolic content and reduced ascorbic acid in comparison to vertically grown herbs ^{(Reference Neveu, Perez- Jimenez and Vos2,3)} . The study has provided baseline values of secondary metabolites in vertically farmed leafy herbs and has indicated that these crops can vary in serving as sources of antioxidant compounds.