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swelling is rapid during the first 5 to 10 minutes at a certain temperature but
continues upon further heating [29]; however, the prolonged holding of temperatures at about 95 to 96°C does not seem to increase the swelling to a great
extent [28,110,114]. The swelling is not affected by presoaking before heating
but does increase with increasing water-to-starch ratios up to 25 ml water per
g starch. The swelling was reported to increase as a result of defatting the
starch [29], although for oat and pigeon pea starches defatting seems to
decrease swelling [111–113].
The heating procedure influences the swelling (e.g., increased shearing
has been found to increase the swelling) [28]; however, severe shearing will
cause fragmentation of the granules [61]. Another parameter of importance is
the heating rate. For maize and wheat starches at 90°C, the swelling ratio was
higher for the higher heating rate, the effect being greater for wheat compared
with maize [114].
It is evident from Figure 10.4 that different starches show different swelling
patterns, with regard to both the final gel volumes obtained and the temperature
response. As can be seen from Figure 10.4, potato starch gives a very large
gel volume. The waxy varieties show the highest gel volumes when starches
differing in amylose content are compared [29,84].
10.3.2.6 Leaking
During heating and at the same time as the absorption of water, material is
leached out from the starch granules. The material is largely amylose, although
amylopectin might be leached, the amount depending on the starch and the
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