Inhibition of oxidation of omega-3 polyunsaturated fatty acids and fish oil by quercetin glycosides Gwendolyn M. Huber a , H.P. Vasantha Rupasinghe a, * , Fereidoon Shahidi b a Department of Environmental Sciences, Nova Scotia Agricultural College, Truro, NS, Canada B2N 5E3 b Department of Biochemistry, Memorial University of Newfoundland, St. John’s, NL, Canada A1B 3X9 article info Article history: Received 26 January 2009 Received in revised form 29 March 2009 Accepted 1 April 2009 Keywords: Omega-3 PUFA Fish oil Lipid oxidation TBARS Quercetins Flavonols BHT a-Tocopherol abstract The antioxidant properties of naturally occurring flavonols, quercetin glycosides, were examined and compared with common food antioxidants butylated hydroxytoluene (BHT) and a-tocopherol. Antioxi- dants were incorporated into selected polyunsaturated fatty acids (PUFA) or fish oil in aqueous emulsions and bulk oil systems. The effectiveness of quercetin was similar to or greater than quercetin glycosides in inhibiting lipid oxidation in the oil-in-water emulsion systems when oxidation was induced by heat, light, peroxyl radical or ferrous ion. In bulk fish oil, C-3 glycosylation enhanced the antioxidant activity of quercetin. The effectiveness of quercetin and its glycosides was greater than that of a-tocopherol in the emulsions. Quercetin and quercetin-3-O-glucoside exhibited a better antioxidant activity than BHT in bulk fish oil; however, the reverse was observed in the emulsions of omega-3 PUFA and fish oil systems in agreement with the polar paradox theory. Quercetin and its glycosides were more effective than a-tocopherol in emulsion systems. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Dietary lipids, fatty acid profiles and their balance in food and within the body have received considerable attention in recent years. This is due to a better recognition that low levels of ome- ga-3 fatty acids may be implicated in several chronic diseases (Shahidi & Miraliakbari, 2004, 2005; Simopoulos, 2002). As a result, omega-3 fatty acid-containing functional foods and nutraceuticals have been introduced into the market. However, highly unsatu- rated fatty acids (HUFA) in such oils are vulnerable to oxidation, thus producing various aldehydes and ketones that render unac- ceptable colours, odours and flavours in polyunsaturated fatty acid (PUFA) containing foods and nutraceutical products (Nawar, 1996). Moreover, products of lipid oxidation, such as propanal, acrolein and malonaldehyde, among others, possess adverse health effects due to their cytotoxic and genotoxic effects (Esterbauer, Schaur, & Zollner, 1990; Fang, Vaca, Valsta, & Mutanen, 1996). The high rate of oxidation of PUFA can be controlled by the addition of syn- thetic or natural antioxidants such as butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), tert-butylhydroquinone (TBHQ) and a-tocopherol. Recently, consumer health conscious- ness has led to a demand for ‘natural’ alternatives to synthetically produced food antioxidants. Flavonols are a sub-group of flavonoids, found ubiquitously in fruits, vegetables and many medicinal and aromatic plants (Rupa- singhe, 2008). Quercetin, a common flavonol, has been shown as an effective antioxidant in several in vitro systems such as the oxygen radical absorbance capacity (ORAC) (Ou, Hampsch-Woodill, & Prior, 2001), the ferric reducing antioxidant power (FRAP) (Pulido, Bravo, & Saura-Calixto, 2000) and the 1,1-diphenyl-2-pic- rylhydrazyl (DPPH) radical scavenging assays (Kemertelidze, Tsits- ishvili, Alaniya, & Sagareishvili, 2000). When compared to other flavonoids, quercetin has been shown to prolong the lag time be- fore the initiation of low density lipoprotein (LDL) oxidation effec- tively (Safari & Sheikh, 2003). As well, quercetin has also been shown to inhibit lipid oxidation in cereal grains (Viscidi, Dougher- ty, Briggs, & Camire, 2004) and marine oils rich in PUFA (Wanas- undara & Shahidi, 1998; Montero, Giménez, Pérez-Mateos, & Gómez-Guillén, 2005; Nieto et al., 1993). Heat-induced cholesterol oxidation can also be reduced by incorporation of 0.002% (w/w) quercetin (Chien, Hsu, & Chen, 2006). In plants, quercetin occurs in the glycosylated forms such as glucoside, galactoside, rhamnoside, arabinoside and rutinoside (Herrera & Luque de Castro, 2004). In fruits such as apples, glyco- 0308-8146/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2009.04.007 * Corresponding author. Address: Tree Fruit Bio-product Research Program, Department of Environmental Sciences, Nova Scotia Agricultural College, P.O. Box 550, Truro, Nova Scotia, Canada B2N 5E3. Tel.: +1 902 893 6623; fax: +1 902 893 1404. E-mail address: vrupasinghe@nsac.ca (H.P. Vasantha Rupasinghe). Food Chemistry 117 (2009) 290–295 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem