Results, Discussion and Conclusion
From particle size distribution, the highest portion of rice flour was on the 180 μm particle size, amounting to 17.4 % whereas the smallest particle size portion passed through the 75 μm sieve was about 12%. Table 1 showed chemical and physical properties of each flour fraction. As particle size reduced, the protein content of the flour seemed to decrease whereas ash content showed opposite results. However, the amylose content of all flour fractions was similar ranging between 30.8 and 32.5%. For WAI and WSI, it was clear that the smaller particle size gave the higher value of these two properties. The smaller particle size fraction exhibited whiter color as L-value increased whereas yellow color was potentially reduced as b-value decreased.
Table 1. Chemical compositions, water absorption index, water solubility index and color value of dry-milled rice flour from different fractions.
The result from RVA showed that the gelatinization temperature (GT) of different flour fractions was affected by particle size (Table 2). GT was reduced as particle size decreased. This may be due to that the smaller particle size fractions could rapidly absorb water and quickly swell resulting in easily gelatinizing of starch at lower temperatures. Peak viscosity, breakdown viscosity, and final viscosity of higher particle size fractions were inversely lower than those of the smaller particle size. These results were similar to the work of (5) who reported that the finer particle size starch reached the onset temperature quicker and exhibited higher thickening behavior than that of the larger particle size. For the setback