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

Abstract

Plant nutrient management can influence the type and level of polyphenolic compounds within leafy vegetables. Therefore, we investigated the effects of fertilizer micro-dosing and harvest time on antioxidant activities of aqueous polyphenolic extracts from Amaranthus cruentus, Ocimum gratissimum and Solanum macrocarpon. Plants were cultivated using urea alone or combined with cattle manure for three staggered harvest periods. Polyphenolics profile (RP-HPLC), DPPH, hydroxyl and superoxide radical scavenging activities, ferric ion reducing power, ferrous ion chelation and inhibition of linoleic acid oxidation were determined. Polyphenolic contents of A. cruentus (caffeic acid, myricetin, quercetin and rutin) and O. gratissimum (catechin and gallic acid) as well as antioxidant activities of the vegetables extracts (except hydroxyl radical scavenging by A. cruentus) were fertilizer micro-dose and harvest timedependent. Thus, combination of both factors highlighted the screening of optimal farming conditions for these vegetables in order to get leaf extracts possessing higher polyphenolic contents and antioxidant activities.

Inhibition of the in vitro Activities of α-Amylase and Pancreatic Lipase by Aqueous Extracts of Amaranthus viridis, Solanum macrocarpon and Telfairia occidentalis Leaves

“…Foods are well known sources of enzyme inhibitory compounds, but their levels could be dependent on agronomic practices, which are critical for defining crop productivity, nutrient composition, and food availability. Therefore, in order to ensure food supply and increase crop productivity, the positive effect of mineral fertilizers cannot be overemphasized ( 28 , 29 ). The use of fertilizer micro-dosing gives promising results in terms of crop productivity and farmers' income when compared to the traditional fertilizer broadcasting method.…”

“…The use of fertilizer micro-dosing gives promising results in terms of crop productivity and farmers' income when compared to the traditional fertilizer broadcasting method. Fertilizer micro-dosing is a method of fertilizer application in small quantities at an optimal depth and distance around the target crop such as leafy vegetables ( 29 , 30 ) and maize ( 31 ) either during the time of planting or some weeks after planting. Water is a universal solvent with numerous advantages as a green extraction solvent because it is cheap, non-flammable, non-toxic, environmentally friendly, and prevent pollution when compared to organic solvents ( 32 ).…”

New Mutant Amaranth Varieties as a Potential Source of Biologically Active Substances

“…Aqueous extracts of A. cruentus leaves showed antioxidant activity against the superoxide radical in the range from 1.0% to 46.9% [ 35 ]. The antioxidant activity of ethanol leaf extracts against the superoxide radical was measured as 1.08 ± 0.09%.g −1 DM (variety ‘Zobor’) and 1.63 ± 0.14%.g −1 DM (variety ‘Pribina’) in our research.…”

“…Gallic acid had 65.4 ± 0.85% activity, which is comparable to the aqueous extract. It has also been found that with increasing concentration of extract, the antioxidant activity against the hydroxyl radical increases in aqueous leaf extracts of A. cruentus [ 35 ]; it ranged from −2.7% to 68.9%. The substances present in the amaranth leaves of both varieties, ‘Pribina’ and ‘Zobor’, were more effective against the hydroxyl radical than they were against the superoxide, though in the latter case, it was due to the long incubation time (40 min).…”

“…The amount of total phenolic compounds per gram of dry matter in the water extract was 1.55 ± 0.098 mg.g −1 DM, in the methanol extract 1.51 ± 0.13 mg.g −1 DM and the ethyl acetate extract had the lowest content of 0.46 ± 0.039 mg.g −1 DM. The content of rutin depending on the dose of fertilizer (2402.0 mg.g −1 ) and the date of harvest time (2279.0 mg.g −1 ) was determined in the aqueous leaf extract of A. cruentus [ 35 ]. In our experiments, we have found the amount of total phenols in the ‘Pribina’ variety 38.1 ± 12.01 mg.g −1 DM and in the ‘Zobor’ variety 26.1 ± 0.33 mg.g −1 DM.…”