Application of ohmic heating in cooking mixtures of brown rice and whole grains: total phenolic content, antioxidant activities, vitamin B1, some minerals, and energy consumption

Abstract

ABSTRACT Brown rice and whole grains are vital nutrient sources for humans; however, they usually require a long cooking period and are difficult to cook uniformly. This study investigated electrical conductivities of brown rice (KDML 105, Riceberry, and red cargo rice) and whole grains (lotus seed, red kidney bean, and Job’s tear) under various conditions. Furthermore, ohmic heating was applied in cooking the mixtures of brown rice and whole grains and the results were compared with conventional heating. The key objective was to apply ohmic heating in cooking the mixtures of brown rice and whole grains to improve the retention of nutrients in cooked products and to improve process efficiency. It appeared that electrical conductivities of all samples were sufficiently high for applying ohmic heating. Electrical conductivities of lotus seed mixed with water were between 0.061 and 0.402 S/m at 30–100°C that were higher than red kidney bean (0.016–0.256 S/m) and Job’s tears (0.018–0.148 S/m). Brown rice of Riceberry variety had the highest electrical conductivities (0.067–0.204 S/m) followed by red cargo rice (0.067–0.173 S/m) and KDML 105 (0.048–0.130 S/m). Sample mixtures cooked using ohmic method had significantly higher antioxidant activities and the calcium, phosphorus, and potassium contents than those cooked using conventional method. Precooking steps for lotus seed, red kidney bean, and Job’s tears were needed with the conventional cooking approach; however, these were unnecessary with ohmic cooking. Ohmic cooking apparatus in this study consumed approximately 2% more energy than electric rice cooker.