Metabolite profiling of flavonols and in vitro antioxidant activity of young shoots of wild Humulus lupulus L. (hop)

Humulus lupulus L., commonly named hop, is well-known for its sedative and estrogenic activity. While hop cones are widely characterized, only few works have been carried out on the young shoots of this plant. In the light of this, the aim of this study was to identify for the first time the flavonoids present in young hop shoots and to compare the composition of samples harvested from different locations in Northern Italy with their antioxidant activity. The samples were extracted by means of dynamic maceration with methanol. The HPLC-UV/DAD, HPLC-ESI-MS and MS2 analysis were carried out by using an Ascentis C18 column (250 × 4.6 mm I.D., 5 μm), with a mobile phase composed of 0.1 M formic acid in both water and acetonitrile, under gradient elution. Quercetin and kaempferol glycosides were the main compounds identified and quantified in hop shoot extracts. Total flavonols ranged from 2698 ± 185 to 517 ± 48 μg/g (fresh weight). The antioxidant activity was determined by means of the radical scavenging activity assay against diphenylpicrylhydrazyl (DPPH[rad]) and by using a photochemiluscence assay with a Photochem® apparatus. The results showed that hop shoots represent a new source of flavonols; therefore, they can be useful for a possible incorporation in the diet as a functional food or applied in the nutraceutical ambit.