Abstract
Rice is the staple food that normally cooked before consumption. Rice cooking usually
involving heating, influences on the microstructure and physicochemical property of grain.
It would also affect the starch digestibility of cooked grain. This study aimed to investigate
the effect of microwave cooking on the starch fractions, morphological damages and starch
digestibility of cooked pigmented rice. Three cultivars of Thai pigmented rice, Hom Nin, Red
Hommali and Kum Luempua, were used in this study. They were soaked in water at ratio 1:4.5
(rice:water, w/v) at 4°C for 19 hours. The soaked rice was cooked using microwave oven at
600W for 12 minutes, and then allowed to incubate at 30°C for 30 minutes to equilibrate
moisture in the grain. The morphological structure of cooked grain was observed using
fluorescent stereomicroscope. The moisture content, total starch content and resistant starch
content were determined. The starch digestibility of cooked rice slurry during simulated in
vitro digestion was also examined. The morphological structure of cooked grain revealed that
cracks were found inside the grain during cooking and the bran layer of Hom Nin and Kum
Luempua was more damaged than that of Red Hommali. Hom Nin showed significantly higher
moisture content (%) (67.26±0.46) than Red Hommali (60.70±0.33) and Kum Luempua
(60.54±1.19) (P<0.05). However, the total starch (%) and resistant starch content (%) found
in Red Hommali was the highest (73.76±1.25; 0.18±0.03) followed by Hom Nin (71.44±0.75;
0.13±0.01) and Kum Luempua (71.23±2.09; 0.09±0.01), respectively. The starch hydrolysis
(%) was increased during the simulated intestinal digestion process, in which Hom Nin
obviously showed the highest value than the others. In conclusion, microwave cooking caused
the morphological damages of grains with varying degree among cultivars which would affect
to starch content
