4.4 Polysaccharides 319Table 4.25.Physicochemical properties of starches before (1) and after (2) heat treatment in the wet state (T=
100 ◦C,t=16 h, H 2 O=27%)
Property Wheat starch Potato starch1212Start of gelatinization (◦C) 56. 5616060. 5
End of gelatinization (◦C) 62 74 68 79
Swelling capacity at 80◦C (ratio) 7. 15 5. 94 62. 30 19. 05
Solubility at 80◦C(%) 2. 59 5. 93 31. 00 10. 10
Water binding capacity (%) 89. 1 182. 6 102. 00 108. 7
Enzymatic vulnerability 0. 44 48. 55 0. 57 40. 35
(% dissolved)Fig. 4.27.Gelatinization temperature of differently hy-
drated starches (— potato starch,−·−wheat starch,
determined by differential thermal analysis, differential
calorimetry, and double refraction) (according toGal-
liard, 1987)
potato starch, while that of wheat starch clearly
increases. The explanation put forward to explain
these findings is that the amorphous amylose
of potato starch is converted to an ordered,
less soluble state, while the amylose of cereal
starch, present partially in the form of helices
with enclosed lipids, changes into a more easily
leachable state.
A gelatinization curve for potato starch is pre-
sented in Fig. 4.29. The number of gelatinized
Fig. 4.28. X-ray diffraction diagrams of potato
starch before (1) and after (2) thermal treatment
(102◦C/16 h) at a water content of 40%. The pattern
of native starch (18.3% of water) corresponds to the
B-type and that of treated starch (24.2% of water) to
the A-type (according toGalliard, 1987)starch granules was determined by microscopy.
Another way to monitor gelatinization as a func-
tion of temperature is to measure the viscosity
of a starch suspension. The viscosity curves in
Fig. 4.30 show that, as mentioned above, the vis-
cosity initially increases due to starch granule
swelling. The subsequent disintegration of the
swollen granule is accompanied by a drop in vis-
cosity. The shape of the curve varies greatly for
different starches.
Potato starch shows a very high maximum
(∼ 4000 Brabenderunits), followed by a steep
drop. Waxy corn starch exhibits similar behavior,
except that the maximum is not as high. In nor-
mal corn starch, the maximum is still lower, but
the following drop is slight, i. e., the granules are
more stable. Under these conditions, amylomaize
starch does not swell, even though ca. 35% of