Abstract
This study examined the physicochemical properties of three kinds of black rice — Okunomurasaki (nonwaxy, Japonica), Asamurasaki (waxy, Japonica), and Nursery sticky rice (waxy, Indica) — and compared them with the properties of two kinds of unpolished white rice: Koshihikari (nonwaxy, Japonica) and polished Koshihikari.
The water absorption rate of the unpolished black rice was lower than that of the polished rice, but was higher than that of unpolished Koshihikari. Both Nursery sticky rice and Asamurasaki absorbed a remarkable amount of water during cooking. In addition, because Asamurasaki had a fast water absorption rate, it required low starting temperatures and energy levels to gelatinize. In raw black rice, sucrose was the most abundant of the free sugars and sugar loss during rinsing was the least, which could be due to the outer skin of its grain. Furthermore, its glucose content increased significantly upon cooking. Although the polyphenol content of its outer skin reduced slightly after rinsing, its antioxidant activity remained high throughout the cooking process. Cooked waxy black rice was softer and more adhesive than the other tested rice. These results suggest that Asamurasaki black rice is the most suitable for cooking without mixing in polished rice.
