Abstract
The present study was conducted to investigate the antioxidant potential of 11 medicinally or economically important plant materials indigenous to Pakistan. The materials were extracted with 80% methanol and examined for their antioxidant activity under different storage conditions using sunflower and soybean oils as oxidation substrates. Preliminary antioxidant activity assessment among the extracts was conducted with the TLC-test and by measuring percent inhibition of linoleic acid peroxidation. The rhizome of Iris germanica , leaves of Lawsonia alba, and M. oleifera , coffee ( Coffee arabica ) beans, rice ( Oryza sativa ) bran, wheat bran and oats ( Avenis sativa ) groats and hull, which showed higher antioxidant activity among the extracts, were further evaluated using soybean and sunflower oils as oxidation substrates. The vegetable oils were stabilized with extracts at a dosage of 0.12% (w/w), and individually subjected to accelerated (65 o C, 15 days) and ambient (6 months) storage. The oxidative deterioration level was monitored for the measurement of antioxidant activity index (AI), peroxide value (PV), conjugated dienes and trienes contents. Overall, the extracts of coffee beans, oat groats and hull, Iris germanica and M. oleifera leaves were found to be the most effective in extending oxidative stability, and retarding PV, primary and secondary oxidation products of soybean and sunflower oils. The order of efficiency of the plant extracts for stabilization of the subject oils was as follows: oat groats and hull > coffee beans > M. oleifera leaves > Lawsonia alba > Iris germanica > rice bran > wheat bran. Significant differences in the antioxidant potential of some of the extracts for stabilization of substrate oils were observed under ambient and accelerated storage conditions and thus demonstrated a variable antioxidant prospective of the extracts under different analytical protocols.
Highlights
Lipid peroxidation in fats and fatty foods deteriorates their quality and brings about chemical spoilage, and generates free radicals and reactive oxygen specieswhich are implicated in carcinogenesis, mutagenesis, inflammation, aging and cardiovascular diseases (Pezzuto and Park, 2002; Shahidi, 1997; Siddhuraju and Becker, 2003)
The whole data are the mean of duplicate samples, each sample analyzed in triplicate (n = 2x3)
In Thin-Layer Chromatography (TLC) assay, methanolic extracts (ME) of oat, groats and hull exhibited the highest intensity of resulting orange color which might be attributed to the presence of a high amount of phenolic compounds
Summary
Lipid peroxidation in fats and fatty foods deteriorates their quality and brings about chemical spoilage, and generates free radicals and reactive oxygen specieswhich are implicated in carcinogenesis, mutagenesis, inflammation, aging and cardiovascular diseases (Pezzuto and Park, 2002; Shahidi, 1997; Siddhuraju and Becker, 2003). Synthetic antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxyltoluene (BHT), and ter-butyl hydro quinone (TBHQ) are effective in the protection of unsaturated fats and oils and are, used as potential inhibitors of lipid peroxidation to stabilize fat-containing foodstuffs. The use of these synthetic antioxidants in foods is discouraged because of their toxicity and carcinogenicity (Shahidi, 1997; Jeong et al, 2004). Such antioxidants have been restricted recently, as they may cause liver swelling and influence liver enzyme activities (Siddhuraju and Becker, 2003)
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