Effects of parboiling, storage and cooking on the levels of tocopherols, tocotrienols and γ-oryzanol in brown rice (Oryza sativa L.)

Vitamin E and gamma-oryzanol display a wide range of biological activities including hypocholesterolemic, anti-inflammatory and antioxidant activities. Although white rice is far more popular worldwide, consumption of brown rice is increasing, partially on account of the presence of bioactive compounds; however, the effects of parboiling, storage and cooking on them are not well-characterized. The effects of parboiling and a 6-month storage period on the contents of vitamin E and gamma-oryzanol in three brown rice cultivars grown in three different locations in Brazil were investigated. Also, their levels in branded non-parboiled and parboiled brown rice were monitored before and after cooking. Vitamin E homologues and gamma-oryzanol were separated by RP-HPLC equipped with FDA and fluorescence detectors. The average levels of total tocols and gamma-oryzanol in the raw brown rice cultivars studied were 25 and 188 mg/kg, respectively. Of the vitamin E homologues, gamma-tocotrienol contributed with 74% of total tocols, followed by alpha-tocopherol, alpha-tocotrienol and gamma-tocopherol in minor quantities. The combined processes, parboiling, storage and cooking, led to an approximate 90% reduction in tocols and only gamma-tocotrienol was detectable after any of the processes. Parboiling followed by storage resulted in an approximate 40% loss of gamma-oryzanol. Cooking had almost no further effect over gamma-oryzanol levels in parboiled rice previously stored for 6 months. (C) 2011 Elsevier Ltd. All rights reserved.