Changes of starch during parboiling of rice kernels

• Freshly, one-month aged, and commercial parboiled rice were studied.
• Parboiling at 110 °C for 20 min destroyed all the crystallinity of starch.
• Maltese cross remained in some granules throughout parboiling even though starch was not crystalline.
• Starch granules from parboiled rice could swell four times in glycerol and still showed Maltese cross.

The morphologies of starch granules within rice kernels were examined immediately after the steaming process (110 °C for 20 min) and after aging of the parboiled rice. Freshly, one-month aged, and commercial parboiled rice were studied to better understand the parboiling process. Starch was completely gelatinized as determined by differential scanning calorimetry, and X-ray diffraction, indicating the disruption of all short-range crystallinity of starch in parboiled rice. However, scanning electron microscopic images showed some intact starch granules, and light microscopic images showed starch granules embedded in the center of the rice kernel. Interestingly, these granules displayed Maltese cross patterns. For the first time, we demonstrated that parboiled rice starch granules could swell in glycerol to four to five times of its original size but still showed Maltese cross.