Changes in Physicochemical Properties of Parboiled Brown Rice during Heat Treatment

Thai rice varieties with high amylose content (Chainat 1, Supanburi 1) and low amylose content (Koa Dok Mali 105) were used to produce parboiled brown rice. In this study brown rice with the initial moisture content of 13±1 % (w.b.) was soaked at two different initial soaking temperatures of 70 and 80o C. The soaking time was 1h, 2h, 3h and 4h, followed by steaming at temperature of 100oC for 10, 15 and 20 min. The samples were then shade dried at 30±1o C and 60±5 %RH to a final moisture content of 13±1 % (w.b.). Physicochemical properties were determined and sensory analysis was performed for selected processing conditions. Head rice yield, yellowness (b-value), whiteness, hardness, water absorption, vitamin E and vitamin B2 were measured and compared with those of commercial parboiled paddy. Results revealed that the head rice yield, color (b-value), cooking time and hardness of parboiled brown rice were decreased whereas whiteness and water absorption were increased compared with commercial parboiled paddy. Qualitatively, parboiled brown rice showed intermediate values between milled rice and commercial parboiled paddy. Sensory analysis revealed high acceptance of cooked parboiled brown rice from the panelists. However, presence of vitamin B2 decreased and vitamin E disappeared after parboiling process on brown rice. Head rice yield was lower for parboiled brown rice when compared to that of parboiled paddy but greater than the head rice yield of non-parboiled rice.