Evaluation of Antioxidant Activity of Garden Thyme (Thymus vulgaris L.) Affected by Humic Acid Under Urmia-Iran Condition

Abstract

The trial aimed to study the effects of different levels of humic acid on the antioxidant activity of garden thyme. The study was conducted at the experimental fields of the Agronomy Department, Faculty of Agriculture, Urmia University, West Azerbaijan, Iran, and used randomized complete block design with four replications. Three different humic acid doses; 200 kg ha−1, 400 kg ha−1 and 600 kg ha−1, and control with no humic acid were the treatments. Total phenolic content, total flavonoid content, DPPH (1,1-diphenyl 2-picryl hydroxyl) radical scavenging activity, nitric oxide radical scavenging activity, and chain-breaking activity were determined. According to the results, the effect of different levels of humic acid in the first harvest on total flavonoid content and nitric oxide radical scavenging was significant whereas, in the second harvest, total phenols content, total flavonoids content, DPPH radical scavenging activity, and chain-breaking activity were significant. The maximum total phenolic content, and nitric oxide radical scavenging activity were obtained in the control treatment. The highest total flavonoid content, DPPH radical scavenging activity, and chain-breaking activity were obtained in the application of 400 kg ha−1 and 600 kg ha−1 humic acid.