3.5. Swelling power of starches
The native rice starches significantly increased their swelling
powers when heating temperature was higher than 60 C (Fig. 2).
The swelling powers of waxy rice starches increased from 5.0 to32.4 (g/g) when starch slurry was heated from 60 to 90 C, whereas
the swelling powers of normal and high-amylose rice starches
were significantly lower than those of the waxy rice starch (2.4–
13.2 and 3.1–13.8 g/g, respectively). After acid and heat-moisture
treatments, the swelling powers of the treated starches significantly
reduced as compared to those of the native starches. The
normal and high-amylose rice starches treated with citric acid
hardly swelled, whereas these starches treated with lactic acid or
acetic acid only swelled when heating temperatures were more
than 70 C. The treated waxy rice starches hardly swelled in all
cases. The less water-holding capacity of the acid and heat-moisture
treated starches was due to the presence of the short chainlength
molecules produced by acid hydrolysis. The degradation of
starch due to partial acid hydrolysis of amylose and amylopectin
in both crystalline and amorphous regions resulting in reduction
of pasting properties of the treated starches were also observed
by other previous studies (Haros, Perez, & Rosell, 2004; Shin, Lee,Kim, Lee, et al., 2007). In addition, the reduction in swelling power
of starch was due to the increased interactions between amylose
and amylopectin molecules, strengthened intramolecular bonds
and formation of amylose–lipid complexes during heat-moisture
treatment (Zavareze & Dias, 2011).