Physicochemical and Morphological Analyses on Damaged Rice Starches
JIH-JOU CHEN1, CHENG-YI LII1 AND SHIN LU2*
1. Institute of Chemistry, Academia Sinica, 128, Sec. 2, Academia Rd., Nangang District, Taipei City 115, Taiwan (R.O.C.)
2. Department of Food Science, National Chung-Hsing University, 250 Guoguang Rd., South District, Taichung City 402, Taiwan (R.O.C.)
(Received: December 31, 2002; Accepted: May 5, 2003)
ABSTRACT
Two types of rice cultivars, indica type (Tainung Sen 19, TNuS19) and waxy (Taichung Waxy 70, TCW70) were used as samples to investigate the changes in the physicochemical properties of damaged rice starch by ball-milling treatment. Rapid Visco Analyzer (RVA) analysis indicated that onset temperature (To,h), peak viscosity (P), setback (C-H), and cold-paste viscosity (C) decreases were more pronounced in TNuS19 than in TCW70 starch during the ball-milling treatment. Similar phenomena were also found in peak temperature (Tp) and enthalpy changes (ΔH) by differential scanning calorimetry (DSC), and the peak intensities measured by X-ray diffraction. However, both types of starch showed that extended treatment time resulted in higher median particle size (PS 50). Polarized light micrographs showed that damaged starch granules lost their birefringence, suggesting that the order structure of starch granule was disrupted. The morphological changes in the microstructure of rice starch during ball-milling treatment was also examined by scanning electron microscopy (SEM). The results indicated that TNuS19 starch granules may be more susceptible to mechanical action than TCW70 starch.
Key words: rice starch, ball-milling, damaged starch, rice cultivar changes