Efeitos da parboilização do arroz (Oryza sativa L.) integral sobre os compostos bioativos e a disponibilidade do amido

Abstract

PASCUAL, C.S.C.I. Effects of the parboiling process in brown rice (Oryza sativa L.) on its both bioactive components and starch availability. São Paulo, 102p. FCF/USP, 2010. Rice (Oryza sativa L.) is consumed mostly in the milled form. However, due to its content of bran, vitamin E and -oryzanol, the intake of brown rice has been recommended. Although previous studies ascribed some important health benefits related to these brown rice"s compounds, information regarding the effect of cooking, storage and parboiling on these substances remains to be elucidated. Rice parboiling is a hydrothermal process consisting of soaking, heating and drying that provide technological and nutritional benefits to the consumer. Until now, if parboiling process decreases the starch digestibility and consequently reduces the glycemic index (GI) is unclear. The objectives of the present study were: to evaluate the effect of the parboiling process on starch digestibility through a GI estimation by the kinetics of starch hydrolysis in rice cultivars with different levels of amylose; to analyze the effect of traditional parboiling, cooking and storage for six months on the stability of bioactive components as well as to correlate the content of bioactive components of rice with its antioxidant activity before and after parboiling. Thirty-six samples of brown rice and parboiled brown rice harvested in 2007 and 2008 were analyzed. In addition, three commercial cultivars of both brown and parboiled brown samples from local market that were obtained in São Paulo were also studied. The glycemic index (IG) was estimated from the hydrolysis index (IH). Vitamin E homologues and oryzanol were extracted simultaneously with methanol and analyzed by HPLC-RP/UV and fluorescence detection in a single run. Peak areas were converted to the corresponding by the standards of αand -tocopherol, αand -tocotrienol and oryzanol. The antioxidant capacity was evaluated by both, DPPH • and ORAC methods. The results indicated that starch digestibility from all rice samples was little affected by parboiling under the conditions employed in the present study. Samples with intermediate amylose content had the lowest HI (p <0.05). The estimated GI in raw and parboiled samples was 80% in all rice cultivars selected and in commercial samples as well. The parboiling showed no effect on GI. The total tocols and orizanol contents in raw rice were 25 and 188 mg/kg, respectively. The vitamin E homologues were the most affected by parboiling, storage and cooking than oryzanol with a decrease of 50% or more when compared to the raw grain. However, -oryzanol was more stable during either treatment with 20% loss of when compared to raw rice. The most significant correlation between the concentration of bioactive compounds and antioxidant activity was found for vitamin E.