Barley for Food and Health: Science, Technology, and Products

WHOLE-GRAIN PROCESSING 113
β-amylase, α-glucosidase, lipase, phospholipase, and limit dextrinase. There are
a host of other enzymes that become active in the germination process, such
as superoxide dimutase and catalase, that eliminate peroxide by reacting it with
other compounds, such as polyphenols. A range of enzymes (nucleases, phosphatases,
nucleotidases, and nucleoside deaminases) are possibly involved in
influencing flavor-enhancing nucleotides. Phytase regulates phosphate release
from phytic acid and various isoforms of β-galactosidases. Additionally, enzymes
present in the aleurone, such as endochitinase, protect the kernel against invasive
microorganisms. Endo-β-glucanase, which specifically acts on sections of
β-glucan molecules with contiguous β-(1 → 3) linkages between the glucosyl
moieties in the cell walls, is also thought to have a role in protecting against
invasive microflora. Gibberellins (plant hormones) are produced in the embryo
with the influx of moisture, stimulating enzyme synthesis and activity in the
aleurone tissue (MacLeod et al. 1964).
It would seem that these extremely active and diverse enzyme systems would
be entirely effective in modifying barley to the smallest intact carbon molecule or
mineral component. However, the β-glucans, which are major components of the
endosperm cell walls, present problems in modification, filtration, and brewing,
a fact that has been recognized for many years (Bamforth 1982; Bamforth and
Barclay 1993). It was suggested that the rate of modification of different samples
of barley is determined principally by their content of β-glucan and their ability to
synthesize β-glucanase. High rates of modification correlate with low β-glucan
and high β-glucanase levels (Henry 1989). Conversely, Masak and Basarova
(1991) concluded that barleys which are less readily modified develop levels of
β-glucanase similar to those in readily modified barleys, but that the β-glucans
in the former break down more slowly.
The two main categories of malt are standard malt, which has high diastatic
power and a good supply of complex carbohydrates needed for alcoholic beverage
production, and specialty malt, which is dried at higher temperatures for a longer
time to develop unique flavors and color. Specialty malts are usually intended
for uses in food products (Briess Industries, Inc., Chilton, Wiscousin). The most
extensive use for barley malt is for the first category, a source of fermentable
sugars for alcoholic beverage fermentations. Malt contributes to the flavor and
color that are uniquely characteristic of beverages, so much so that a specific
beverage product is dependent on the malt for these characteristics to a large
degree. Indeed, individual brewers, both large and small, are quite specific in their
demands for barley cultivars and conditions during malting to assure consistency
in their products. Food or specialty malts are used in lesser quantities, but are
added to a number of foods in small amounts, including cooked breakfast cereals,
nonalcoholic beverages, sausages, cake mixes, cookies, and other baked foods.
Barley cultivars and malting conditions are tightly controlled to produce malts
meeting color, flavor, and individual use requirements.
The three basic steps in the malting process are steeping, germination, and
kilning (drying). One of barley’s advantages over other cereal grains for malting
is the presence of an adhering husk to protect the developing acrospires (sprouts)