Nettle (Urtica dioica L.) seeds as a source of free and bound phenolics: The antioxidant, antimicrobial activity and the composition

Abstract

In this study, the composition and the antioxidant and antimicrobial activity of free and bound phenolics from Urtica dioica L. seeds were studied. The composition of phenolics was determined by isocratic and gradient HPLC methods, and the an-tioxidant activity by determining DPPH scavenging capacity, reducing the power and FRAP value. The antimicrobial activity was tested by using the discdiffusion method. The content of free phenolics was higher (6000.71 µg gallic acid equivalent per g dry seeds mass) than the content of bound phenolics (2801.16 µg g-1). The extract of free phenolics had a higher FRAP value than the bound, while the bound phenolics had a better DPPH scavenging capacity and the reducing power. Eighteen phenolics have been detected in the free phenolic extract, among which kaempferol 3-O-rutinoside-7-O-rhamnoside was the most abundant (428.55 µg g-1), while ten phenolics have been detected in the bound phenolic extract, among which monocaffeoyl-meso-tartaric acid (406.83 µg g-1) was the most abundant. Both of the extracts have shown a good inhibitory effect on Bacillus cereus ATCC 11778 and Klebsiella pneumoniae ATTC 700603. The study showed that nettle seeds are a good source of natural antioxidants and antimicrobials for potential use in the food and pharmaceutical industry.