3. Results and discussion3.1. Swell

3. Results and discussion
3.1. Swelling power and solubility
Swelling power and solubility curves of high-, medium- and
low-amylose rice starches are presented in Fig. 1. The swelling
power of the native and HMT starches increased as a result of
increasing the assay temperature (Fig. 1a and c), due to starch gelatinisation. Starch gelatinisation involves the collapse of the starch
granule manifested in irreversible changes in properties such as
granular swelling, native crystallite melting, loss of birefringence
and starch solubilisation (Collado & Corke, 2003). When the temperature of a starch suspension is higher than the gelatinisation
temperature, hydrogen bonds are broken and water molecules
can then penetrate into the granules and hydrate free hydroxyl
groups making it swell (Limberger, Silva, Emanuelli, Comarela, &
Patias, 2008). However, for rice starch with a low-amylose content
(Fig. 1e), the swelling power reached its maximum at 70C; temperatures above this only increased the soluble fraction (Fig. 1f).
The swelling power of the low-amylose starch is higher than
that of the medium- and high-amylose starches, which was also
observed bySasaki and Matsuki (1998), who found an inverse correlation between amylose content and swelling power of wheat
starch.
The swelling power of HMT starches was reduced with rising
moisture content in the treatment as compared to the native
starches. This phenomenon was observed with temperatures above
70 and 80C for high amylose content starches.