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

GENETICS AND NUTRIENT COMPOSITION 79
was distributed in all portions of the kernel. Calcium was highest in the aleurone,
with smaller amounts in the lemma and endosperm cell walls. Magnesium and
phosphorus were most concentrated in the aleurone, with lesser amounts in the
endosperm. Sulfur and chlorine were confined to cell walls of the aleurone and
endosperm.
Potassium and phosphorus are the most abundant minerals in barley, and the
latter is possibly the most important in nutritional terms. Phytic acid (myoinositol)
is the most abundant form of phosphorus in barley, representing 65 to 75% of
total kernel phosphorus (Raboy 1990). Phytic acid is localized in barley embryo
and aleurone tissues (O’Dell et al. 1972), with 80% found in the embryo and
20% in the aleurone. Phosphorus in phytic acid is considered bound and unavailable
for utilization by monogastric animals, as they do not possess the enzyme
phytase in the digestive tract. However, in preparing foods with alkali treatment,
phosphorus in phytic acid becomes biologically available. A major disadvantage
of unaltered phytic acid is that divalent cations such as calcium, copper, and
zinc are irreversibly chelated with phosphorus in the molecule, making them
nutritionally unavailable.
Very little genetic research has been conducted on the mineral content of
barley, with the exception of phosphorus (Ullrich 2002). Mutant barley genotypes
that have significantly reduced the level of phytic acid have been developed by
U.S. Department of Agriculture scientists (Larson et al. 1998; Raboy and Cook
1999). The low-phytic-acid barley shows a reduction of 50 to 75% in phytic acid
phosphorus with no obvious change in total seed phosphorus. Compared with
normal barley, phosphorus in the low-phytic-acid barley has been shown to be
more available to fish (Sugiura et al. 1999), swine (Veum et al. 2002), and poultry
(Li et al. 2001a, b). Two genes responsible for the low-phytic-acid mutations,
lpa1 and lpa2 , have been mapped to chromosomes 2(2H) and 1(7H), respectively
(Larson et al. 1998). Cultivars with homozygous lpa1 gene have various amounts
of phytic acid phosphorus reduction, with a concomitant increase in inorganic
phosphorus and no change in total phosphorus. In homozygous lpa2 cultivar
types, kernel phytic acid phosphorus is reduced, accompanied by an increase
in inorganic phosphorus. The genetics, breeding, and nutritional implications of
low-phytic-acid cereals, including barley, has been thoroughly reviewed (Larson
et al. 1998; Raboy et al. 2001; Dorsch et al. 2003). Although mineral element
concentrations are known to be affected by variety (genetics), as in the case of
the low-phytic-acid mutant, growing season, soil type, moisture, and fertility, will
also have measurable effects (Kleese et al. 1968; Owen et al. 1977).
Phytochemicals
Phytochemicals are compounds occurring in plants, other than the basic recognized
nutrients, that are reported to have protective actions against certain types of
cancer, cardiovascular disease, and degenerative diseases such as arthritis, often
due to their antioxidant activity. These compounds are sometimes referred to as