Variation of antioxidant activity and phenolic compositions of Marrubium vulgare L. as influenced by organic acids

In sustainable agriculture, reduction of chemical fertilizers- induced environmental pollutions is mainly considered. Therefore, recently application of organic fertilizers particularly their foliar applications received increased attention. Besides, herbal medicine with higher antioxidant activity will be able to limit the formation of free radical species.

Therefore, we aimed to determine the effect of foliar application of organic fertilizers on antioxidant activity and polyphenolic compounds of Marrubium vulgare L. in greenhouse experiment.

In a completely randomized design experiment with three replications that was carried out in 2019, the applied treatments consisted of four levels (0, 250, 500, and 1000 mg L-1) of foliar application of humic and fulvic acids (0, 250, 500, and 1000 mg L-1). Some phenolic compounds including gallic acid, chloregenic acid, coumarin, hesperidin, and eugenol were detected and quantified in the Marrubium vulgare L. extracts.

Application of 250 mg humic acid L-1 resulted in the highest extraction of phenolic compounds, coumarin, reducing this content at a higher applied level and by fulvic acid addition. As such, the foliar application of low concentrations of humic acid before the flowering stage was a useful and effective method to increase the synthesis of phenolic compounds. Among the studied organic acids, the application of 250 mg humic acid L-1 showed the highest antioxidant activities. These compounds can be effective in controlling diseases with free radicals.

Based on the findings of the present research, a more appropriate management of the growth and propagation of medicinal plants and their quality can be applied. In addition, humic substances application reduces the chemical fertilizers used, thereby maintaining the environment.