Changes in antioxidant attributes of mint (Mentha arvensis L.) as affected by foliar application of selected plant growth enhancers

The study mainly investigated the effect of exogenous applications of selected plant growth enhancers (PGEs) on the yield of extractable antioxidant components, the total phenolic content (TPC) and the antioxidant activity of mint (Mentha arvensis L.). PGEs including humic acid (HA, 10%, 25% and 30%), 6-benzyl amino purine (6-BAP at 25 ppm, 50 ppm, and 75 ppm), and Moringa oleifera leaf extract (MOLE, fresh, 1-month-old and 2-month-old) were applied as foliar treatments. Humic acid (HA) was also used as a seed priming agent wherein the seeds were spread in HA solution for 6 h, 9 h and 12 h, respectively, prior to sowing. The second seed priming agent bio-fertilizer (BF) was applied in slurry form to seeds for 30 min before sowing. Analysis of the PGE-applied mint samples relative to the control showed that the total phenolic content was 6.297–21.043 mg GAE/g of dry matter (DM); reducing power was 0.542–1.911 (at 10 mg/mL extract concentration); and the 2,2-diphenyl-1-picryhydrzyl (DPPH) free radical scavenging capacity (IC50) was 0.212–0.504 µg/mL, indicating a significant improvement (enhancement) in the antioxidant attributes of the plants. Generally, the MOLE-applied mint samples had greater phenolic and antioxidant activity compared with the other treatments, showing the effectiveness of exogenous applications of Moringa plant material in enhancing the yield and functional food value of the herb.