Chemical and Functional Properties of Food Saccharides

Log Rz
3
2.8
2.6
2.4
2.2
2
1.8
© 2004 by CRC Press LLC
1.6
7 7.5 8 8.5 9 9.5 10
Log Mw
FIGURE 7.1 Relationships between the weight-average molecular weight (M w) and zaverage
gyration radius (R z) of amylopectin. Data are plotted on Log-Log scale; normal Atype
(£), B-type (Ø), C-type (r) amylopectin; waxy A-type (¢), B-type (ø) amylopectin;
and cyanobacterial glycogen (Å). The linear regression line on the graph comprises data of
the A-type amylopectin, r = 0.98 (P 13) that develop to the
B-type crystalline structure. 42 X-ray diffraction signals and space distances calculated
from the signals reveal that the A-type polymorphic form of starch crystal has
a monoclinic packing unit, which consists of seven sets of double helices closely
packed in the unit and contains only two water molecules in each unit. 2,3 The Btype
crystalline packing is the same as that for amylose crystals. The sizes of
crystalline lamellae of A- and the B-type starch granules are similar, for example,
9.0 nm for maize and 9.2 nm for potato, determined by x-ray diffraction 31 and the
small angle electron scattering method. 43
Structures of Naegeli dextrins prepared from starches of A- and B-type polymorphisms
are quite distinct. The Naegeli dextrins of B-type polymorphic starches
consist of a small number of branched molecules, whereas those of A-type starches
consist of large proportions of branched molecules (Figure 7.2). These distinct