Beer : Health and Nutrition

116 Chapter Five
An antioxidant-rich material unique to the production of beer is hops (De Keukeleire
et al. 2001). These authors report:
The diversity of natural hop constituents undoubtedly accounts for the varied and
rich panoply of bioactivities hitherto reported: sedative, antistress, sopori c activities,
estrogenicity, treatment of complaints related to the menopause, anticancer
properties (in particular inhibition of hormone-dependent cancers of breast, uterus
and prostate), bacteristatic activity, anti-in ammatory action, stimulation of the
digestive tract, diureticum and agent against bladder complaints, diaphoretic and
perspiration-stimulating effects, and anaphrodiasiacum.
The active ingredients of the hop are laid down in lupulin near the end of the growing
period with a primary purpose of protecting the plant against pests. The prenylated
avonoids are a family of compounds restricted to a relatively small number of plant
families. Prenylated avonoids are present in lupulin glands at levels from 0.2–0.6%,
while up to 4 ppm of prenylated avonoids can be found in beer.
Stevens et al. (1999b) found that the prenylated avonoids, including xanthohumulone,
are largely isomerised during wort boiling and lost as a result of incomplete
extraction from hop and adsorption onto wort proteins and yeast cells. Consequently only
22–30% ends up in beer. Some 10% of the hop desmethylxanthohumol and the 3′-geranylchalconaringenin
survive into beer in the form of prenylnaringenin. De Keukeleire
et al. (1997b) reports up to 21 ppb 8-prenylnaringenin in beers, although Stevens et al.
(1999a) report up to 240 ppb. The levels will depend on the mode of hopping.
Forster et al. (2002) demonstrated that the xanthohumol levels in beer can be enhanced
using xanthohumol-rich hop preparations. This substance is ordinarily lost to a sizeable
extent during the brewing process, but by introducing more into the stream, especially
later on in the process, levels might be raised. The scope for tailoring raw materials
to enhance the levels of potentially healthful components of beers is considerable
– ‘functional beers’? Certainly the prenylated chalcones from hops and beer have been
shown to be effective in combating lipid oxidation in model systems based on rat liver
microsomes (Rodriguez et al. 2001).
Potentially deleterious components of beer
Baxter et al. (2001) employed arti cially high levels of ochratoxin A to show that most
is probably lost as a result of proteolysis in mashing, through adsorption on spent grains
and during fermentation. However, in these studies some 13–32% survived into beer. It
is clearly necessary to ensure that the levels of these materials in raw materials are as low
as possible. Blank (2002) observed that the main sources of mycotoxin in the diet were