Submitted to: Cereal Foods World
Publication Type: Abstract Only
Publication Acceptance Date: 9/14/2010
Publication Date: 10/25/2010
Citation: Chen, M., Min, B., Mcclung, A.M. 2010. Effect of steam-cooking and parboiling on phenolics and antioxidant capacities of red and purple rice cultivars. Cereal Foods World. 55:A21.
Technical Abstract: Red and purple rice cultivars contain high concentrations of phenolics, such as proanthocyanidins and anthocyanins, respectively. We investigated the effect of cooking processes on these antioxidants and antioxidant capacities of pigmented and common light-brown bran rice. The cooking processes included whole-grain steam-cooked (S), paddy (with hull) parboiled (PP), parboiled paddy steam-cooked (PP-S), whole-grain parboiled (PW), and parboiled whole-grain steam-cooked (PW-S). Uncooked whole-grain (Raw) served as a control. Raw red and purple rice cultivars had 3- to 20-fold higher total phenolic (TP) and total flavonoid (TF) concentrations, DPPH radical scavenging capacity and ORAC oxygen radical absorbance capacity than did the raw light-brown bran rice. The cooking processes, in general, decreased TP, TF, DPPH and ORAC among all rice cultivars in the following pattern, from least to greatest decrease compared to Raw: S < PP < PP-S < PW < PW-S. The concentration of proanthocyanidins relative to that in Raw decreased as the intensity of the cooking processes increased, and were highly correlated with those of TP, TF, DPPH and ORAC. Concentrations of proanthocyanidins were 42% and 12% of Raw in S and PP-S samples, respectively. Anthocyanins were quite heat sensitive. Concentrations of anthocyanins in purple rice cultivars averaged 29% and 1.6% of Raw in S and PP-S samples, respectively. However, heat-resistant phenolic compounds were present since the % TP, TF, DPPH and ORAC of purple rice ranged from 83 to 95% and from 46 to 75% of Raw in S and PP-S samples, respectively. Phenolics in light brown bran rice were relatively more resistant to cooking processes than those in pigmented rice. Nevertheless, one of the steam-cooked purple rice cultivars, for example, still had 6.8- and 18-fold higher ORAC and TF, respectively, than did the common light-brown rice.