Abstract
Black-kerneled rice contains antioxidants, making it of interest to consumers. However, it is much more expensive than common rice, and this is one of the problems for the food industry to utilize. To supply cheaper raw materials for the food industry, we assessed the polyphenol content and heat gelatinization properties of the screenings of ‘Shiho’ black-kerneled glutinous rice developed in Niigata Prefecture. Screenings of 1.70−1.85 mm grain thickness had 26.1% less polyphenol than refined grain, and screenings of \<1.70 mm had 54.3% less. Therefore, to achieve the same polyphenol yield as from refined grain, it would be necessary to use 30% to 50% more rice screenings. The rate of decrease of polyphenol content was lower per unit weight than per kernel, and it seems that flour made from screenings would reduce the necessary amount of raw materials in comparison with whole grains. Thinner grain had a higher protein content than thicker grain, and screenings of \<1.7 mm had 8.6% protein. In addition, the gelatinization start temperature was lower, and the rice cake hardening rate of rice screenings seemed to be lower than those of refined grain. The heat gelatinization properties of rice screenings also seemed to be inferior. Flour made from screenings would have a lower swelling capacity, a weaker gel strength, and slower starch retrogradation than that made from refined grain. It will be necessary to solve these problems before rice screenings can be used in the food industry. A supply route also needs to be established.
