Antioxidative effects of stabilized and unstabilized defatted rice bran methanolic extracts on the stability of rice bran oil under accelerated conditions

Maznah Ismail,Norsharina Ismail,Abdalbasit Adam Mariod,Hadiza Altine Adamu

doi:10.3989/gya.110309

Abstract

The present research assessed the antioxidant activity against the synthetic 1, 1-diphenyl-2-picrylhydrazyl radical, and β-carotene-linoleic acid assay of the methanolic extracts of defatted rice bran from stabilized and unstabilized rice bran. The effects of the extracts (0.1 and 0.25% w/w) on the oxidative stability of refined-bleached rice bran oil were determined and compared with those of BHA (synthetic antioxidant). The study was carried out over a 168 hr period at 70°C and the progression of oxidation was measured by peroxide value, p-anisidine value, and thiobarbituric acid-reactive substances (TBARS). The relative % of residual α-tocopherol and γ-oryzanol of the rice bran oil containing methanolic extracts of stabilized and unstabilized defatted rice bran during storage at 70°C were studied.

Highlights

Many studies have focused on rice bran as a source of natural antioxidants e.g. rice bran (Chotimarkorn et al, 2008) and defatted rice bran (Devi and Arumughan, 2007), which is the predominant byproduct of rice bran oil and a good source of insoluble dietary fiber, protein, phytic acid, inositol and vitamin B (Hargrove, 1994)
The different extracts were dissolved in a small amount of methanol and applied to rice bran oil at levels of 0.25 and 0.5% to examine their antioxidative activity; the development of the peroxide, anisidine, conjugated deine (CD), and TBRAS values during the oxidation of rice bran oil were evaluated at 70°C for 168 hour
The results in this table reveal that the stabilized rice bran (SRB) exhibited a higher phenolic content of 519.6 mg/100g gallic acid equivalents (GAE) followed by the unstabilized rice bran (USRB) extract (480.1 mg/100g)

Summary

Introduction

Many studies have focused on rice bran as a source of natural antioxidants e.g. rice bran (Chotimarkorn et al, 2008) and defatted rice bran (Devi and Arumughan, 2007), which is the predominant byproduct of rice bran oil and a good source of insoluble dietary fiber, protein, phytic acid, inositol and vitamin B (Hargrove, 1994). The antioxidant potential of defatted rice bran was determined (Shin et al, 1992; Devi et al, 2007), but it still remains a relatively unexplored source material, which demands further investigation especially with regards to its phytochemical composition related to possible health benefits as antioxidants. Stabilized and unstabilized defatted rice bran extracts have not been investigated as a source of natural antioxidant substitutes for synthetic antioxidants in bulk oil during storage. The changes in the antioxidative components of crude defatted rice bran extracts have not been explored during autoxidation. The objectives of this research were to investigate the phenolic compounds of stabilized and unstabilized defatted rice bran extracts and to evaluate their antioxidant activity (AOA) using different in vitro methods. The different extracts were dissolved in a small amount of methanol and applied to rice bran oil at levels of 0.25 and 0.5% to examine their antioxidative activity; the development of the peroxide, anisidine, conjugated deine (CD), and TBRAS values during the oxidation of rice bran oil were evaluated at 70°C for 168 hour

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