3.5. Physical properties of treated flour
SEM images of the original white rice flour (BRF) and those of
the treated rice flour (SYN-GRF) are shown in Fig. 1(a, c) and (b,
d), respectively. It can be seen that before the treatment, starch
granules appear as clump in the matrices of plant cell wall. Sonication
treatment releases starch granules by breaking plant cell wall
matrices (Fig. 1b). Starch granule shape changed from nearly
spherical before treatment (Fig. 1c) to polygonal (Fig. 1d). This
polygonal shape can be reasoned as the artifact of NaOH abrasion
of starch granule surface, which is commonly identified as amyloplast.
Since amyloplast is a non-pigmented plant organelle that is
strongly associated with protein bodies (i.e., enzyme) for starch
synthesis and stored lipid, removal of amyloplast also contributes
to the reduction of protein and lipid content in rice flour after
treatment. Since low power ultrasound was utilized in this study,
the surface of starch did not develop any remarkable pore or pitch
(Jambrak et al., 2010).