Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
TABLE 17.1
Characteristics of α-, β- and γ-CD
Characteristic α β γ
No. of glucose units 6 7 8
Molecular weight 972 1135 1297
Solubility in water
(g/100 ml) at room
temp.
14.5 1.85 23.2
[α] D at 25°C 150 ± 0.5 162.5 ± 0.5 177.4 ± 0.5
Cavity diameter (Å) 4.7–5.3 6.0–6.5 7.5–8.3
Height of torus (Å) 7.9 ± 0.1 7.9 ± 0.1 7.9 ± 0.1
Diameter of outer
periphery (Å)
14.6 ± 0.4 15.4 ± 0.4 17.5 ± 0.4
Approx. volume of
cavity (Å3 )
174 262 427
Approx. cavity
volume in 1 mol CD
(ml)
104 157 256
Approx. cavity
volume in 1 g CD
(ml)
0.10 0.14 0.20
Crystal forms (from Hexagonal plates Monoclinic
Quadratic prisms
water)
parallelograms
Crystal water (wt%) 10.2 13.2–14.5 8.13–17.7
Diffusion constants at
40°C
3.443 3.224 3.000
Hydrolysis by A.
oryzae α-amylase
Negligible Slow Rapid
pK (by potentiometry)
at 25°C
12.332 12.202 12.081
Partial molar volumes
in solution (ml/mol)
611.4 703.8 801.2
Adiabatic
compressibility in
aqueous solutions
(ml/mol/ bar ×104 )
7.2 0.4 –5.0
fairly rigid structure. The intramolecular hydrogen bond formation explains the
lowest water solubility of β-CD among all CDs.
The hydrogen-bond belt in the α-CD molecule cannot be completed because
one glucopyranose unit takes a distorted position. Consequently, only four hydrogen
bonds are formed instead of the six required hydrogen bonds. γ-CD is the non-coplanar,
more flexible molecule and is therefore most soluble among all the CDs.
Figure 17.2 demonstrates characteristic structural features of CDs. On the side
with the secondary hydroxyl groups, the cavity is wider than on the other side
carrying the freely rotating primary hydroxyl groups.