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

GENETICS AND NUTRIENT COMPOSITION 73
contains about 67% of the neutral lipids of the grain total. Nonpolar lipids represent
about 75% of the total lipids in the whole grain, with the remaining 25%
somewhat evenly divided between glycolipids and phospholipids (polar lipids).
In general, this same ratio of nonpolar and polar lipids is representative of lipids
in bran, endosperm, aleurone, embryo, and hull.
Nonstarch lipids are stored in oil droplets called spherosomes surrounded by
a membrane. These membranes contain polar lipids, principally phospholipids
(Morrison 1993b). The principal nonpolar lipid in the droplets is triacylglycerol,
with the remainder being comprised of steryl esters, diacylglycerol, monoacylglycerol,
and free fatty acids. The major fatty acids in barley triacylglycerol are
palmitic acid (16 : 0), oleic acid (18 : 1), linoleic acid (18 : 2), and linolenic acid
(18 : 3), comprising approximately 23, 13, 56, and 8%, respectively of the total.
The saturated fatty acid stearic acid (18 : 0) makes up less than 1% of the total
(Anness 1984; Morrison 1993a). Morrison (1993a) also noted that the fatty acids
in barley are similar to those in wheat except that barley tends to have more
linolenic acid than wheat. Larger barley kernels tend to have higher values for
palmitic acid and lower values for linoleic and linolenic acids (De Man and
Bruyneel 1987). Variety, growing environments, and nitrogen fertilization were
reported to have only small effects on fatty acid composition (De Man 1985; De
Man and Dondeyne 1985).
Starch lipids are located inside starch granules and in quantities generally
proportional to amylose content. The true starch lipids are almost exclusively
phospholipids (Morrison et al. 1984; Morrison 1988, 1993a); however, Acker and
Becker (1971) found a small amount (4.4%) of free fatty acids, in a sample of
barley starch lipid along with phospholipids. These authors reported that palmitic
acid was the predominant acid in the free fatty acids, followed by linoleic and
oleic acids in that order. Tester and Morrison (1992) reported differences in
the fatty composition of starch lipids isolated from waxy and nonwaxy barleys.
Palmitic acid and linoleic acid contents varied inversely in total starch lipids
of waxy and nonwaxy mature grains. Total starch lipids in waxy barley contained
about 30% more palmitic acid and about 30% less linolenic acid than did
nonwaxy barley.
Genetic selection and breeding for increased total lipids in barley kernels have
met with only limited success. Price and Parsons (1974) reported finding a barley
cultivar (CI 12116) grown in South Dakota that contained 4.6% total lipid, but
subsequent samples of this barley grown at two locations in Canada contained
normal (2 to 3%) lipid levels (Fedak and de la Roche 1977; Bhatty and Rossnagel
1979). The high-lysine mutant Risø 1508 was reported to contain higher levels
of total lipids (Bhatty and Rossnagel 1979; Newman et al. 1990; Munck 1992);
however, it was suggested by Morrison (1993a) that the increased levels were
due to the severely shrunken endosperm of the mutant barley. However, it is
worthy of note that a high-lysine cultivar (CA 700202) developed from Risø
1508 in Denmark (Bang-Olsen et al. 1987) has plumper kernels with a higher
starch content than the mutant parent, yet maintains the higher level of total
lipids (Newman et al. 1990). Another shrunken endosperm mutant that has waxy