Influence of nitrogen fertilizer micro-dosing on phenolic content, antioxidant, and anticholinesterase properties of aqueous extracts of three tropical leafy vegetables

Abstract

This work investigated the effect of fertilizer micro-dosing on in vitro antioxidant and antiacetylcholinesterase (AChE) properties of aqueous extracts of leaves of three vegetables (Solanum macrocarpon L., Amaranthus viridis L., and Telfairia occidentalis f. Hooke). Urea was combined (0, 20, 40, and 60 kg/ha) with cow manure (5 t/ha) or without cow manure (80 kg/ha) to grow the leafy vegetables. Significantly higher (p < .05) polyphenol extract yield was obtained with 60 kg N/ha when compared with other fertilizer doses. Total polyphenol (510.70-521.50 mg gallic acid equivalent/g) and total flavonoid (609.51-742.50 mg rutin equivalent/g) contents were reduced as fertilizer dose increased. The 2,2-diphenyl-1 picrylhydrazyl radical scavenging and iron reducing properties were enhanced by organic manure while metal ion chelation and anti-AChE activity was highest at the 60 kg N/ha. We conclude that the combined use of organic manure with urea fertilizer led to enhanced antioxidant and anti-AChE activities of the leaf polyphenolic extracts. Practical applicationsThe search for natural scavengers of free radicals as food preservatives and nutraceutical agents has intensified in the past decade because of increasing negative reactions to synthetic compounds by consumers. Vegetable leaf polyphenolic compounds used in this work showed free radical scavenging and other antioxidant properties that are comparable to those of butylated hydroxytoluene, a synthetic antioxidant agent. The polyphenol extracts also showed acetylcholinesterase (AChE)inhibitory property that is similar to that of galanthamine, a drug used for the treatment of Alzheimer's disease. Since oxidative stress is also associated with the development of chronic diseases, the vegetable leaf extracts are potential agents that can be used both as effective food preservatives and bioactive agents against neurodegenerative diseases. K E Y W O R D S acetylcholinesterase, antioxidant, free radical scavenging, nitrogen fertilizer, polyphenols, vegetable leaves

Fertilizer micro-dosing and harvesting time of indigenous leafy vegetables affect in vitro antioxidant activities

“…Thus, nitrogen micro-dosing associated with organic fertilizer for growth of leafy vegetables that will be harvested at early maturity stage could be considered as beneficial to synthesis and activity of water-soluble free radical-scavenging polyphenols. Significant decreases in DPPH-RSA and FRAP with increase of nitrogen application doses as well as increase in these antioxidant activities with co-application of mineral and organic fertilizers had also been previously reported (Olarewaju et al, 2018;Sossa-Vihotogbé et al, 2013b;Stefanelli et al, 2011). High level of antioxidant activities found at the first two harvests could be linked to fertilization (for the first harvest) and to injury stress caused by first leaf harvest (for the second harvest).…”

“…Polyphenolic compounds were identified and quantified according to Olarewaju et al (2018) method with slight modifications. This method used a reversed-phase high-performance liquid chromatography system and was performed with a Varian 900-LC series system (Agilent Technologies, Santa Clara, California, USA) fitted with a C18 analytical column (250 × 4.6 mm, 5 µm) (Phenomenex Inc., Torrance, California, USA) pre-heated to 30 °C.…”

“…Vegetables, including leafy vegetables, contribute to a balanced and healthy diet because of the quality of their phytochemicals (vitamins and polyphenols), which can exert various antioxidant activities (Oboh et al, 2016;Olarewaju et al, 2018;Tavarini et al, 2015). Consumption of indigenous vegetables is rooted in dietary habits of Africans with Amaranthus cruentus (Amaranthaceae), Ocimum gratissimum (Lamiaceae) and Solanum macrocarpon (Solanaceae) belonging to a class of nutritionally and medicinally beneficial leafy vegetables (Achigan-Dako et al, 2010).…”

Effect of Organic (Jatropha Cake) and NPK Fertilizers on Improving Biochemical Components and Antioxidant Properties of Five Cowpea (Vigna unguiculata L. Walp.) Genotypes

“…It is also reported that M. olefeira treated with NPK and compost (50 + 50%) in combination, depicted higher phenolics and flavonoids contents as compared to the control (Sarwar et al, 2019). According to Olarewaju et al (2018), the increased biomass in treated group can leads to reduced synthesis of secondary metabolites (polyphenolic compounds). The phenolic compounds contents are reduced when the phenylalanine amount is low as the protein accumulation increased when the nitrogen concentration is higher (Jones & Hartley, 1999).…”

Kinetics of acetylcholinesterase inhibition by hemp seed protein‐derived peptides

“…This abberant brain and neurotransmission condition leads to Alzheimer's disease (AD) pathogenesis (Li et al, 2015;Willcox, Scapagnini, & Willcox, 2014) that contributes to increased global morbidity/mortality rate (US Burden of Disease Collaborators, 2013). The high catalytic efficiency (CE) of AChE and the importance of its inhibition in AD management has been an important research focus in the development of various therapeutic agents (Acharya, Dutta, Chaudhury, & De, 2018;Li et al, 2015;Olarewaju et al, 2018;Saravanaraman, Chinnadurai, & Boopathy, 2014;Taslimi & Gulçin, 2018;Yadav & Appukuttan, 2019;Yatesa et al, 2019;Zare-Zardini, Tolueinia, Hashemi, Ebrahimi, & Fesahat, 2013). Several synthetic AChE-inhibitory drugs have been developed for use against neurodegenerative diseases, such as dementia and AD; however, these drugs are associated with severe negative side effects (Ghribia, Ghouilaa, Omrib, Besbesb, & Janneta, 2014;Iannello et al, 2014;Kumar & Chowdhury, 2014).…”