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

GENETICS AND NUTRIENT COMPOSITION 61
Barleys that contain more than the normal amounts of amylose (40 to 70% of
the total) in the starch are classified as high-amylose cultivars. The first reported
high-amylose barley was a mutant of Glacier, a six-rowed feed type, and was designated
Glacier Ac38. This barley was found to contain 44 to 47% amylose in the
starch (Merritt 1967), and Walker and Merritt (1969) subsequently demonstrated
that the amylose level in Glacier Ac38 was under genetic control. The controlling
gene, amo1 , is located on chromosome 5(1H) (Barley Genetics Newsletter 1996).
Morell et al. (2003) conducted a study on shrunken endosperm (sex6) barleys
derived from Himalaya, a hulless nonwaxy variety. They identified two lines,
M292 and M342, having high-amylose phenotypes resulting from a decrease in
amylopectin synthesis. M292 and M342 were found to have amylose contents of
71.0 and 62.5% of the total starch, respectively. The starch properties of these
two lines are unique in that there is an increase in short chains of amylopectin and
the starch has a low gelatinization temperature. Additionally, starch granules of
M292 and M342 have reduced levels of crystallinity, and the crystal shifts from
A-type to a mixture of V- and B-types. V-type starch is typical of amylose–lipid
complexes, indicating that a portion of the amylose in these barleys is complexed
with lipid, which is highly unusual in cereal starches. Genetic analysis revealed
that the gene causing the mutation produced impaired amylopectin synthesis in
these barleys and is located at the sex6 locus on chromosome 7H. Additionally,
it was reported that sex6 starches have shortened amylopectin chain length
compared to the high-amylose starch produced by the amo1 gene in Glacier
Ac38.
Barley starch consists of a mixture of large-diameter (15 to 25 μm) granules
and irregularly shaped granules that are smaller in diameter (