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

72 BARLEY: GENETICS AND NUTRIENT COMPOSITION
original check variety but failed to equal the top-yielding cultivars by the time
of its development. The most complete review of the high-lysine barley breeding
saga and the genetics involved was written by Lars Munck (1992).
Lipids
In a review on barley lipids, Morrison (1993a) stated that lipids have received
much less attention by researchers than other nutritional components, such as carbohydrates
and protein. Even so, this author presented a wealth of information
on barley lipids in his review, including classification, composition, distribution
in the kernel, varietal differences, and relationship with other components. Lipids
are located throughout the barley kernel and are classified into two basic fractions:
nonstarch lipids and starch lipids. Nonstarch lipids include all lipids other
than those inside starch granules. Lipids are also classified as polar or nonpolar,
a characteristic that affects solubility and depends on molecular structure. Additionally,
the term free lipid has been used to describe those lipids that can be
extracted with nonpolar solvents, and bound lipids, those that are extracted with
polar solvents. The proportion of free and bound lipids varies between tissues,
and Morrison (1993a) cautions that it should never be assumed that free lipids
are the same as total lipids.
Morrison (1993a) also cautions that the choice of analytical procedures for
measuring lipid content is critical in accurate determination of the true total lipid
content values and/or accurate separation of the various types and classes of
lipids. Solvent extraction followed by gravimetric measurement is the normal
approach to measuring total lipid content in cereal grains; therefore, effective
extraction depends on proper sample preparation (grinding), choice of solvent,
and acid hydrolysis prior to extraction. Åman et al. (1985) reported that the total
lipid content of 115 barley samples measured after acid hydrolysis ranged from
2.1 to 3.7% (weighted mean = 3.0%). In a later study in this laboratory, Åman and
Newman (1986) reported somewhat higher values in 20 high-lysine (2.6 to 5.9%)
and three high-sugar barleys (4.4 to 7.3%). Lower mean levels of total lipids,
in the range 2.0 to 2.5%, have been reported in older literature and composition
text tables; however, it may be assumed that these values were obtained without
acid hydrolysis prior to extraction (Morrison 1993a). Parsons and Price (1974)
reported total lipid levels ranging from 3.l to 4.6% in 18 varieties that were
extracted with polar solvents. These varying reports emphasize the necessity of
standardized analytical techniques and being certain of the technique utilized
when reporting compositional data.
Lipid is concentrated in the embryo, and although the embryo represents only
about 3% of the kernel by weight, it furnishes about 18% of the total lipid in
barley. The endosperm contains about 3% lipid, but by virtue of size, furnishes
about 77% of the total lipid, Most of the endosperm lipid is found in the aleurone
layer. The remaining 5% of the total kernel lipid is found in the hull (Price
and Parsons 1975, 1979; Briggs 1978). According to Briggs (1978), the aleurone