Acta Hortic. 1236. ISHS 2019. DOI 10.17660/ActaHortic.2019.1236.1 Proc. IV International Humulus Symposium Eds.: P. Matthews and F. Stevens 1 Effect of different extraction solvents on phenolic compounds and antioxidant capacity of hop flowers ( Humulus lupulus L.) M. Mafakheri and Y. Hamidoghli Department of Horticulture Science, University of Guilan, Rasht, Iran. Abstract We investigated the potential of wild hop and determined the effects of different solvent extractions on quality and quantity of hop extracts. Three different solvents – aqueous-ethanol (75%), methanol and acetone – were applied to elicit the secondary metabolites of Humulus lupulus L. cones by automatic Soxhlet system, and extraction yield, total phenolic content, total flavonoid content and antioxidant capacity were compared. The antioxidant activity tests, DPPH, ABTS and FRAP, were used to analyze the antioxidant capacity of extracts. The crude extract obtained by aqueous-ethanol, methanol and acetone extraction were 98.65±5.2, 61.39±3.25, 69.28±4.1 mg g -1 dry matter, respectively. The total phenolic content (TPC) as well as the total flavonoid content (TFC) of aqueous extracts exhibited the highest values. Also the antioxidant activity of extracts was different: the acetone extract had the highest value of IC50 in the DPPH test, while the methanol extract has the highest antioxidant activity (1.79±0.25 mM Fe 2+ g -1 ) in the FRAP test, and the best result of percent inhibitors of ABTS (58.12±0.48) was observed for the aqueous-ethanol extract. In addition, ABTS value in aqueous-ethanol extract was 6.45±0.33 mmol Trolox equivalent g -1 sample, significantly higher than others. No significant correlation was found among antioxidant measurement methods. Overall, 75% ethanol is suggested for the extraction of phenolic compounds from hop flowers due to its polarization diversity. Finally, the wild hop flowers have high antioxidant activity and a remarkable amount of phenolic compounds. They could be applied in food industries as a rich source of antioxidant activity. Characterization of the genetic diversity of wild hops is underway. Keywords: extract, antioxidant capacity, hops, solvent, ethanol, polarity INTRODUCTION Phenolic compounds are secondary metabolites widely found in the plant kingdom. Until now many polyphenolic compound bioactivity effects have been published, with an interest to introduce new cultivars with variant chemical potential (Ligor et al., 2014; Gião et al., 2006). In the northern area of Iran, the best climate for cultivation of hop, there is interest to introduce new crops in large-scale farms, especially those with native occurence. Hop (Humulus lupulus) is a valuable spice source for brewing industry, because of bitterness and aroma characteristics. The quantity and quality of these compounds are very different: each cultivar has its own typical amount of polyphenolic compounds and bitter acids, which are important factors to determine different potential of a hop cultivar as chemotype and ecotype (Neve, 1991; Zanoli and Zavatti, 2008; Kavalier et al., 2014; Ligor et al., 2014). Usually essential oils of hop have been used to identify new cultivars, but recently phenolic compounds are also used to distinguish new potential. Furthermore, prenyl-flavonoids such as 8-prenylnaringenin and xanthohumol are derived from phenolic precursors, and exhibit interesting potential against cancers, viruses and microbes (Possemiers et al., 2006; Steenackers et al., 2015). However, quantitation depends on a suitable extraction system. Because of high polarity of polyphenolic compounds, polar-organic solvents are preferred (Schlesier et al., 2002; OÖnder et al., 2013). Previous studies showed a mixture of different solvents could be more effective on quality and quantity of final extract as a result of diversity of polarity among chemical components. In addition, solvents classified as GRAS