Although female cones of the hop plant (Humulus lupulus) are known primarily as raw material supplying characteristic bitterness and aroma to beer, their equally significant health-promoting effects have been known to mankind for several thousand years and hop is a plant traditionally utilized in folk medicine. This paper summarizes the scientific knowledge on the effects of all 3 major groups of secondary metabolites of hops; polyphenols, essential oils, and resins. Because of their chemical diversity, it is no coincidence that these compounds exhibit a wide range of pharmacologically important properties. In addition to antioxidant, anti-inflammatory, and anticancer-related properties, particular attention is being paid to prenylflavonoids that occur almost exclusively in hops and are considered to be some of the most active phytoestrogens known. Hop oils and resins are well known for their sedative and other neuropharmacological properties, but in addition, these compounds exhibit antibacterial and antifungal effects. Recently, alpha bitter acids have been shown to block the development of a number of complex lifestyle diseases that are referred to by the collective name "metabolic syndrome." Information presented in this review confirms the significant potential for the use of hops in the pharmaceutical industry and provides an understanding of beer as a natural drink that, although moderately consumed, may become a source of many health-promoting compounds.

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Xanthohumol is a hop polyphenol with proven positive effects on human health. The aim of this work was to use special malts (roasted malt and melanoidin malt) for the preparation of high-gravity sweet worts with an extremely high xanthohumol content. The solubility of xanthohumol was higher in sweet worts prepared from roasted malts than from Pilsen or melanoidin malts. This sweet wort (xanthohumol~20 mg L À1 ) was used for the preparation of xanthohumol-rich beer. The importance of melanoidins in xanthohumol solubility was also examined. Isomerization reactions occurring at increased temperatures is one of the main reasons for the loss of xanthohumol in the brewing process and therefore the most appropriate temperature for addition of xanthohumol products to sweet worts was determined. The influence of filtration and stabilization materials (diatomaceous earth, polyamide sorbents and tannic acid) on the concentration of xanthohumol in enriched beer was also examined. Only a small effect of these materials was shown in xanthohumol-rich dark beers, with the exception of tannic acid, which removed a significant amount of this polyphenol.

In recent years, interest in hop-derived constituents, especially for prenylflavonoids has grown, as they have a wide range of biological properties including antioxidant, anticarcinogenic and antimicrobial activities. Two main hop prenylflavonoids, xanthohumol and isoxanthohumol, and hop extract enriched in prenylflavonoids, were tested for their antiproliferative activities on colon cancer cell lines, HT-29 and SW620, and a noncancerous cell line, IEC-6. It was confirmed that both xanthohumol and isoxanthohumol inhibited cell proliferation, even at micromolar concentrations. For cell line HT-29, the IC 50 was 1.2 ± 0.9 and 16.9 ± 0.9 μmol dm À3 for xanthohumol and isoxanthohumol, respectively. Similar values were obtained for SW620 cells (2.5 ± 0.2 and 37.3 ± 3.2 μmol dm -3 ). None of the pure prenylflavonoids that were tested affected the proliferation of the noncancerous cell line, IEC-6. The effect of the hop extract containing xanthohumol was also tested for antiproliferative activities on the cancer cell lines, HT-29 (IC 50 = 3.1 ± 0.2 μmol dm -3 ) and SW620 (IC 50 = 1 ± 0.2 μmol dm À3 ), and on the cell line, IEC-6 (IC 50 = 65.5 ± 11.3 μmol dm À3 ). The results showed a similar trend to that for pure compounds, suggesting a possible future application of hop extracts in the pharmaceutical industry.