Quality controlling of brown rice by ultrasound treatment and its effect on isolated starch

• Ultrasound treatment was applied to brown rice grains at mild and harsh conditions.
• Higher vitamin content was measured in ultrasound treated brown rice than in milled rice.
• The more brown rice hydrated, the greater ultrasound effect was.
• Degradation of weak starch molecules by ultrasound treatment improves the texture of brown rice.

Ultrasonic treatment (UT) was applied to brown rice at two different conditions: mild (25 °C, 30 min) and harsh (50 °C, 60 min) after soaking for several times (2, 3, 5, and 8 h). After UT, starch was isolated from the brown rice grains, and the physicochemical properties of the starch, as well as the textural and nutritional properties of the grains, were compared. After UT, the cooked brown rice grains was softer in proportion to soaking time, and the hardness of brown rice soaked for 8 h and then ultrasound treated at harsh condition was similar to that of cooked milled rice. Untreated brown rice grain has much more thiamin, riboflavin, and niacin contents than milled rice (0.546 vs. 0.069, 0.054 vs. 0.018, and 4.56 vs. 1.21 mg/100 g, respectively), and the thiamin and niacin contents in brown rice treated even at the most harsh condition were still higher than those in milled rice (0.193 vs. 0.069, and 1.6 vs. 1.21 mg/100 g, respectively). The isolated starch from brown rice grains treated at the harsh condition exhibited a lower pasting temperature and higher breakdown in pasting properties than that treated at the mild condition. The crystalline structure of starch became more homogeneous by UT at both conditions with longer soaking times. Both of the melting enthalpy and relative crystallinity of starch significantly decreased by UT, however A-type crystal form was maintained.