THESIS

(Takeda et al. 1986 and Takeda et al. 1993). Rice amylose is a mixture of branched
and linear molecules with a degree of polymerization (DPn) of 1,100-1,700 and 700-
900, respectively (Hizukuri et al. 1989). The branched fraction in rice constituted 25-
50 % by number and 30-40% by mass of amylose. Rice amyloses have a β-
amylolysis of 73–81 %, indicating them to be slightly branched molecules with three
to four chains on average (Hizukuri et al. 1988). This β-amylolysis limit is
considerably higher than that of amylopectin (55-60%). These structural properties of
amylose from rice are similar those of wheat and maize, as indicated in Table 2. The
amylose content of the starch granule varies with the botanical source of the starch
and is affected by climatic and soil conditions during grain development (Morrison
and Azudin, 1987). High temperatures decrease the amylose content of rice, whereas
cool temperatures have the opposite effect. Amylose content of rice is specified as
waxy (0-2%), very low (5-12%), low (12-20%), intermediate (20-25%) and high (25-
33%) (Juliano,1992). Amylose is a roughly linear molecule containing about 99% α-
(1,4) and about 1% α- (1,6) bonds with a molecular weight of 500-20,000 (Figure 3).
Table 2 Structural properties of amylose
Source β-
Amylolysis
limit (%)
Avg.
DPn
Avg.
Number
Chain
Avg.
Chain
Length
Branched
Molecules
Wheat 88 1,300 4.8 270 27
Maize 82 930 2.7 340 44
Rice: Indica 73 1,000 4.0 250 49
Japonica 81 1,100 3.4 320 31
Source: Hizukuri et al. (1989)
(%)
Amylose can form an extended shape (hydrodynamic radius 7-22 nm) but
generally tends to wind up into a rather stiff left-handed single helix or form even
stiffer parallel left-handed double helical junction zones (Swinkels, 1985). Single
helical amylose has hydrogen-bonding O2 and O6 atoms on outside surface of the
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