Flavonoids as Phytoestrogenic Components of Hops and Beer

Abstract

The value of hops (Humulus lupulus L.) in beer production has been undisputed for centuries. Hops is rich in humulones and lupulones which gives the characteristic aroma and bitter taste, and preserves this golden drink against growing bacteria and molds. Besides α- and β-acids, the lupulin glands of hop cones excrete prenylated flavonoids, which exhibit a broad spectrum of biological activities and therefore has therapeutic potential in humans. Recently, interest in hops was raised due to hop prenylated flavanones which show extraordinary estrogen activities. The strongest known phytoestrogen so far is 8-prenylnaringenin (8-PN), which along with 6-prenylanaringenin (6-PN), 6,8-diprenylnaringenin (6,8-DPN) and 8-geranylnaringenin (8-GN) are fundamental for the potent estrogen activity of hops. This review provides insight into the unusual hop phytoestrogens and shows numerous health benefits associated with their wide spectrum of biological activities including estrogenic, anticancer, neuropreventive, antinflamatory, and antimicrobial properties, which were intensively studied, and potential applications of these compounds such as, as an alternative to hormone replacement therapy (HRT).

Keywords: beer; biological activities; hop; phytoestrogens; prenylflavonoids.

Figure 1

Biosynthesis pathways of several hop flavonoids. PAL: Phenylalanine ammonia-lyase; C4H cinnamate 4-hydroxylase, 4CL 4-coumarate-CoA ligase, AAC acetyl-CoA carboxylase, CS chalcone synthase, HIPT1 Humulus lupulus prenyltansferase-1,CHI chalcone isomerase, OMT O-methyltransferase, F3H flavanone 3-hydroxylase, FLS flavonol synthase, DFR dihydroflavonol 4-reductase, LAR leucoanthocyanidin reductase, ANS anthocyanidin synthase, ANR anthocyanidin reductase, FMO flavonoid 3-monooxygenase, CPR cytochrome P450 reductase, F3′5′H flavonoid 3′5′-hydroxylase.

Figure 2

Structures of described flavonoids: xanthohumol XN (1), isoxanthohumol IX (2), desmethylxanthohumol DMX (3), 8-prenylnaringenin 8-PN (4), 6-prenylnaringenin 6-PN (5), 6,8-diprenylnaringenin 6,8-DPN (6), 8-geranylnaringenin 8-GN (7).

Figure 3

Paths of formation of IXN (2), 8-PN (4) and 6-PN (5) during wort boiling.

Figure 4

Human liver microsomes metabolites (8–19) of 8-PN (4) [40].

Figure 5

Comparison of chemical structures of estradiol (20), isoflavone (equol, (21)) and 8-PN (4) [63].