3. Results and discussion
3.1. Gel texture of rice starch as influenced by annealing and HMT
Results showed that both annealing and HMT apparently increased gel hardness of rice starch (Table 1).
Gel hardness of UR starch was 49.82 g and it increased with increase in temperature and duration time of both treatments.
The mechanical properties of starch gel depend on the volume fraction and rigidity of gelatinized starch granules, as well as the interactions between disperse and continuous phase of gel (Biliarderis, 1998).
These were drastically affected by hydrothermal treatments, resulting
in the apparent changes in gel texture.
By annealing, gel hardness increased to 52.58–60.38 g. Chung et al. (2000) described that annealing caused the ordering rearrangement of starch molecules, resulting in the decreased SP.
Gel volume fraction decreased and led to the increased gel
hardness.
It was found that either increase or decrease in solubility could possibly improve gel hardness.
At high solubility, the gel would become harder because the leached starch molecules form the continuous gel matrix (Lii, Tsai, & Tseng, 1996).
However, at low solubility, gel surface hardness was found to increase (Chung et al., 2000).
These led to the apparent increase in gel hardness following annealing.