Recebido em 8/12/98; aceito em 23/3/99Beer brewing is an intricate process encompassing mixing and further elaboration of four essential raw materials, including barley malt, brewing water, hops and yeast. Particularly hops determine to a great extent typical beer qualities such as bitter taste, hoppy flavour, and foam stability. Conversely, hop-derived bitter acids account for an offending lightstruck flavour, which is formed on exposure of beer to light. These various processes are presented in detail, while due emphasis is placed on state-of-the-art hop technology, which provides brewers with efficient means to control bitterness, foam, and light-stability thereby allowing for the production of beers with consistent quality.

Hop acids, a family of bitter compounds derived from the hop plant (Humulus lupulus), have been reported to exert a wide range of effects, both in vitro and in vivo. They exhibit potential anticancer activity by inhibiting cell proliferation and angiogenesis, by inducing apoptosis, and by increasing the expression of cytochrome P450 detoxification enzymes. Furthermore, hop bitter acids are effective against inflammatory and metabolic disorders, which makes them challenging candidates for the treatment of diabetes mellitus, cardiovascular diseases, and metabolic syndrome. This review summarizes the current knowledge on hop bitter acids, including both phytochemical aspects, as well as the biological and pharmacological properties of these compounds.

The transcription factor NFB plays a critical role in normal and pathophysiological immune responses. Therefore, NFB and the signaling pathways that regulate its activation have become a major focus of drug development programs. Withania somnifera (WS) is a medicinal plant that is widely used in Palestine for the treatment of various inflammatory disorders. In this study we show that the leave extract of WS, as well as its major constituent withaferin A (WA), potently inhibits NFB activation by preventing the tumor necrosis factor-induced activation of IB kinase ␤ via a thioalkylation-sensitive redox mechanism, whereas other WS-derived steroidal lactones, such as withanolide A and 12-deoxywithastramonolide, are far less effective. To our knowledge, this is the first communication of IB kinase ␤ inhibition by a plant-derived inhibitor, coinciding with MEK1/ ERK-dependent Ser-181 hyperphosphorylation. This prevents IB phosphorylation and degradation, which subsequently blocks NFB translocation, NFB/DNA binding, and gene transcription. Taken together, our results indicate that pure WA or WA-enriched WS extracts can be considered as a novel class of NFB inhibitors, which hold promise as novel anti-inflammatory agents for treatment of various inflammatory disorders and/or cancer.

Hops, an essential beer ingredient, are a source of prenylflavonoids, including 8-prenylnaringenin (8-PN), one of the most potent phytoestrogens. Because 8-PN concentrations in beers are generally low, its health effects after moderate beer consumption were considered negligible. However, human intestinal microbiota may activate up to 4 mg/L isoxanthohumol (IX) in beer into 8-PN. Depending on interindividual differences in the intestinal transformation potential, this conversion could easily increase the 8-PN exposure 10-fold upon beer consumption. Here, we present a further investigation of the process both in vitro and in vivo. In vitro experiments with the dynamic SHIME model showed that hop prenylflavonoids pass unaltered through the stomach and small intestine and that activation of IX into 8-PN (up to 80% conversion) occurs only in the distal colon. In vitro incubations of 51 fecal samples from female volunteers with IX enabled us to separate the fecal microbiota into high (8 of 51), moderate (11 of 51) and slow (32 of 51) 8-PN producers, clearly illustrating an interindividual variability. Three women, selected from the respective groups, received a daily dose of 5.59 mg IX for 4 d. Intestinal IX activation and urinary 8-PN excretion were correlated (R(2) = 0.6417, P < 0.01). These data show that intestinal conversion of IX upon moderate beer consumption can lead to 8-PN exposure values that might fall within the range of human biological activity.

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Age-induced decomposition of iso-a-acids, the main bittering principles of beer, determines the consistency of the beer bitter taste. In this study, the profiles of iso-a-acids in selected highquality top-fermented and lager beers were monitored by quantitative high-performance liquid chromatography at various time intervals during ageing. Tlte degradation of the iso-a-acids as a function of time is represented by the ratio, in percentage, of the sum of the concentrations of trans-isocohumulone and trans-isohumulone to the sum of the concentrations of cis-isocohumulone and cis-isohumulone. Tfiis parameter is relevant with respect to the evaluation of bitterness deterioration in aged beers. Trans-iso-a-acids having a shelf half-life of less than one year proved to be significantly less stable than cis-iso-a-acids, but it appears feasible to counteract degradation if a stiitable beer matrix is available. Tlte fate of the trans-iso-a-acids in particular adversely affects beer bitterness consistency. In addition to using hop products containing low amounts of trans-iso-a-acids, brewers may profit of the remarkable stability of tetrahydroiso-aacids, even on prolonged storage, for the production of consistently bitter beers.KeyWords: Hops, iso-a-acids, tetrahydwiso-a-acid$, beer bitterness, beer ageing, HPLC analysis. INTRODUCTION associated with beer ageing, because such compounds, in particular /nms-2-nonenal, are considered responsibleOrganoleptic consistency of beer is of paramount for the so-called cardboard or staling offimportance to the modern brewing industry2. Raw navour3.6.io.2<>3:>.42.43. An array of enzymic and chemical materials are in general well characterised and reactions are supposed to be involved in the formation technological innovations continuously lead to of ageing carbonyls, including melanoidin-catalysed improvements in the brewing process, yet reproducible oxidation of higher alcohols1516, oxidative reactions of production of flavour-stable beers remains a challenging iso-a-acids4151617'2"-34, Strecker-type degradation of amino task for a brewer. In particular, lager beers are liable to acids61516 '28-11'32,auto-oxidation1516-27'32,photo-oxidationS7;w, undergo rapid taste and flavour changes that can readily and enzymic degradation7827^7 of unsaturated fatty acids, be tracked. Beer deterioration is an extremely complex aldol-type condensations of short-chain aldehydes1516, process, while, moreover, various beer types age in ancj secondary auto-oxidation of aIdehydes15l6--»2. different ways2. Importantly, the relative significance of these various pathways is not clear and even the nature of precursorsIn particular, the formation of volatile unsaturated for the carbonyls has not been unequivocally established43, carbonyl compounds with 6 to 10 carbon atoms has beenAmong the non-volatiles in beer, the iso-a-acids are *To whom correspondence should be addressed. pre-eminent as the main bitter principles. The iso-ct- Age-induced decomposition of iso-a-acids acids comprise 6 major components, ...

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Important secondary metabolites, present in hops (Humulus lupulus L.), include alpha-acids and beta-acids, which are essential for the brewing of beer, as well as the prenylated chalcones, desmethylxanthohumol, and xanthohumol, which exhibit interesting bioactive properties. Their formation and accumulation in five selected hop varieties, Wye Challenger, Wye Target, Golding, Admiral, and Whitbread Golding Variety, were quantitatively monitored by high-performance liquid chromatography using UV detection. All target compounds were present from the onset of flowering, not only in female hop cones but also in male inflorescences, albeit in low concentrations. During development from female inflorescences to cones, levels of alpha-acids, beta-acids, desmethylxanthohumol, and xanthohumol gradually increased, while each hop variety exhibited individual accumulation rates. Furthermore, these compounds were present in leaves of fully grown hops as well. The study demonstrated that key compounds for flavor and potential beneficial health effects associated with beer not only reside in the glandular lupulin structures but also are distributed over various parts of the hop plant.