Antioxidant and anticholinesterase potentials of essential oils of selected aromatic plants under secondary treated effluent irrigation
Background: The shortage of water throughout the world dictates application of marginal water for irrigation. Secondary treated municipal effluent (TE) is a common alternative water source for irrigation in arid and semiarid areas. Aromatic herbs are cultivated as industrial crops for herb essential oil (EO) production. The EOs can play a role as natural antioxidants and enzyme inhibitors targeting human diseases, e.g., Alzheimer’s disease (AD). Such agents can prevent oxidative deterioration of foods, minimize oxidative injury of living cells, treat AD and enhance memory. Replacement of potable water (PW) with (TE) for irrigation of aromatic plants could encourage the expansion of large-scale agro-industrial systems for aromatic crops, and EOs in Palestine. This study was aimed at (1) evaluating the applicability of TE for agricultural crops, (2) assessing the effects of continuous use of treated water on soil and crops, and analyzing the antioxidant and anticholinesterase activities of these plants and their essential oils under irrigation with TE. Materials and Methods: To compare responses of selected aromatic plants to irrigation with PW and TE an experimental field has been established, each treatment consisted of 4 replicated plots. The plants were exposed to the water treatments for two consecutive seasons. EO from fresh plant areal parts of both treatments was obtained during the two seasons (summer and fall 2016) by hydrodistillation. The extracted EOs and methanolic leaf extracts were tested for their antioxidant activity using DPPH scavenging of free radicals and reductive potential (RP), and for acetyl and butyryl cholinesterase inhibitory activity (AChEI and BuChEI) using the NA-FB method. Results: Regardless of the differences in the quality of water, the TE did not affect fresh and dry biomass production, spices output and yield of EO quantity in the crops except for Salvia fruticosa which was statistically significant and increased for all previous yield parameters. Also, water quality did not affect the cholinesterase inhibitory activity of the plants (EOs or extracts). Mentha spicata plant extract showed the highest AChE and BuChE inhibitory activities with selectivity index (SI) of 2.93 and 3.85 in PW and STE, respectively. Whereas it’s EO showed the lowest inhibitory activity against both enzymes. Overall, the tested methanolic extracts were found to be more selective inhibitors of AChE than BuChE, while their EOs were more selective inhibitor on BuChE. The antioxidant activity of the extracts also was not affected by effluent- irrigation, M. spicata, and R. officinalis exhibited the best RP and DPPH-scavenger, whereas the only EOs from O. syriacum and R. officinalis exhibited strong to weak activity as antioxidants. Conclusion: The data demonstrate that TE can be effectively utilized for irrigation of industrial crops for EO, natural antioxidants, and anticholinestrase agents production because the yield and bioactivity were not affected.