Factors affecting the polyphenol compounds and antiradical activity of hops: Long-term study of Czech hop varieties

The influence of polyphenol substances on the quality of beer and its colloidal and sensory stability has been investigated for many decades with often controversial knowledge (derdelinckx). It is a very diversified group of substances whose individual components are characterized by different properties in terms of chemical structure, antioxidant capabilities, haze properties and hence an influence of the beer stability. Hops is a specific raw material that has been investigated for the last few decades from the point of view of pharmaceutical use (Karabín et al., 2016). Secondary metabolites formed in the cones of hop during the flowering and ripening, bitter acids, essential oils and polyphenols are sensorially active and have antioxidant and antimicrobial properties. Hop polyphenolic is very diverse group of biologically active compounds that comprise 3% to 6% of the dry weight of hop cones (Moir, 2000). The majority of polyphenols are located in the strig and bract (“leaf associated polyphenols“), the prenylflavonoids are secreted from lupulin glands together with the bitter acids and essential oils (Almaguer et al., 2014). Hop polyphenols are usually split into groups of flavonols, flavan-3-ols (catechis), phenolic carboxylic acids (groups of benzoic acid and cinnamic acid derivatives) and other phenolic compounds (prenylflavonoids, stilbenoids) (Biendl, 2009). The analytical methods used for the determination of polyphenols are governed by the purpose of their use. Group methods are based on the specific reactivity of a particular group of polyphenols and are included in the brewing analytics. This is in particular the determination of total polyphenols, flavonoids and anthocyanogens. For a detailed description of the profile of a particular group of polyphenol Klíčová slova: chmel (Humulus Lupulus L.), polyfenoly, prenylflavonoidy, antiradikálová aktivita DPPH, odrůdy chmele