Comparison of antioxidant activity of extracts of hop leaves harvested in different years

Abstract

Introduction: Hop (Humulus lupulus L.) is a common plant in Europe, with many beneficial health effects. In addition to the use in brewing, hops are a valuable source of active substances used in conventional and folk medicine, such as humulones and lupulones, as well as antioxidants, including phenolic compounds.Objective: The aim of the study was to evaluate and compare the antioxidant activity of alcoholic extracts of fresh hop leaves collected in 2017 and 2018. Material and methods:The raw material consisting of fresh hop leaves was extracted using ultrasoundassisted extraction. Methyl, ethyl and isopropyl alcohol at three concentrations were used as extractants. The antioxidant activity of extracts was determined using DPPH and FRAP methods. Total phenolic content was evaluated using the Folin-Ciocalteu technique. Results:All the extracts showed antioxidant potential as well as the phenolic content. Regardless of the harvesting year and methods of evaluation, the highest antioxidant activity and the total polyphenol content were observed for extracts prepared in undiluted methanol, obtained during one hour lasting extraction. Conclusion:The results of the studies have suggested that hop leaves can be a potential source of healthpromoting antioxidants.

Humulus lupulus L. as a Natural Source of Functional Biomolecules

“…Polyphenols are a wide group of biologically active secondary metabolites [14,16] whose content and profile depend on the hop variety as well as the different climatic conditions of cultivation [3,16]. The cone bract presents the greatest content of polyphenols in the hop plant, and their content in the cone can fluctuate between 4% and 14% (dry matter) [40].…”

“…In another study, the UAE has been applied with success for the extraction of diverse types of biocompounds from hops. For example, Muzykiewicz et al [3] used this technique with different extractants (methyl, ethyl, and isopropyl alcohol) under three different concentrations to assess the total phenolic content and the antioxidant activity. This research was carried out using fresh hop leaves from different harvested years (2017 and 2018).…”

“…The authors reported that the extracts (from young hop leaves harvested at the starting vegetation) presented a high antioxidant activity, and this antioxidant potential was influenced by different factors (including the solvent type or extraction time) and concluded that the most effective process was using undiluted methanol during one hour of ultrasound-assisted extraction. The antioxidants content depends on the harvesting time and can be also influenced by climatic conditions, among other environmental elements [3].…”

“…It is a species of the genus Humulus that belongs to the Cannabaceae family whose genus origin could be China [2]. It can be found principally in European and in Western Asia deciduous forests and thickets, and in other zone areas with a temperate climate [3]. Hops were cultivated in Babylon around 200 A.D. [4], and they have been in ongoing use for centuries (even a millennium) mainly as a beer ingredient [5].…”

“…The female inflorescences (called hop cones or simply hops) as well as other parts of the plant (leaves, stems, and rhizomes) are rich in different biologically active molecules as polyphenolic compounds and acyl phloroglucides, which are responsible for the different health-promoting effects and bioactivities [3,9]. The lupulin glands, which present a yellow-green color, are located on the hop umbel (in the inner and outer bracteoles) and contain bitter resins and aroma substances [1].…”