Antioxidant activities of annatto and palm tocotrienol-rich fractions in fish oil and structured lipid-based infant formula emulsion Long Zou, Casimir C. Akoh ⇑ Department of Food Science and Technology, The University of Georgia, Athens, GA 30602, USA article info Article history: Received 22 April 2014 Received in revised form 1 July 2014 Accepted 21 July 2014 Available online 30 July 2014 Keywords: Tocotrienol Antioxidant Annatto Palm Structured lipid Fish oil Infant formula Emulsion abstract The abilities of annatto and palm tocotrienol-rich fractions (TRFs), as natural antioxidants, to inhibit lipid oxidation in menhaden fish oil and structured lipid-based infant formula emulsion, were evaluated and compared. The peroxide and anisidine values of the bulk oil and oil-in-water emulsion samples stored at 37 °C were measured over a 28-day period. The results showed that annatto TRF was a more effective antioxidant than palm TRF and a-tocopherol in both food systems at 0.02% and 0.05%. Factors, including structural differences in chromanol head and isoprenoid tail, polarity, concentration, oxidation time, and the method used to monitor lipid oxidation, were responsible for the different behaviours of tocopherols and tocotrienols. In contrast to the reported findings in vivo, addition of a-tocopherol (0–75%) did not interfere with the antioxidant activity of tocopherol-free annatto TRF in foods. Our findings may lead to the development of new natural antioxidant products for food applications. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Lipid oxidation in foods has become a major concern with the increased use of polyunsaturated vegetable, fish, or microbial oils for health benefits. It not only produces undesirable off-flavours, but also decreases the nutritional quality and safety of food prod- ucts (McClements & Decker, 2000), which are unacceptable to con- sumers. Among the methods employed to retard or inhibit oxidation of lipids, addition of antioxidants can be an effective solution (Shahidi & Zhong, 2010; Waraho, McClements, & Decker, 2011). Due to the safety concerns about potentially toxic effects of synthetic additives, there is a worldwide trend toward the use of natural antioxidants (Waraho et al., 2011). Moreover, many nat- ural antioxidants possess additional health-promoting benefits in vivo. Vitamin E compounds (tocopherols and tocotrienols) are con- sidered to be a major group of natural fat-soluble chain-breaking antioxidants to prevent lipid oxidation in foods and biological sys- tems (Eitenmiller & Lee, 2004). Structurally, they are characterized by a chromanol head with two rings (one phenolic and one hetero- cyclic) and a lipophilic isoprenoid tail (Fig. 1). The tocopherols have a saturated phytyl tail, whereas their corresponding tocotrienols have a shorter unsaturated farnesyl tail with three isolated double bonds. The position and number of methyl groups on the chro- manol head determine the specific type of tocopherol or tocotri- enol homologues, named a, b, c, or d. It is widely accepted that the antioxidant activity of tocopherols and tocotrienols is mainly due to their ability to donate phenolic hydrogen to lipid free radi- cals, with less contribution from singlet oxygen quenching (Eitenmiller & Lee, 2004). The more methyl substituents at the ortho- and/or para-position to the hydroxyl group, the more easily can the O–H bond be cleaved (Kamal-Eldin & Appelqvist, 1996; Wright, Johnson, & DiLabio, 2001). Thus, the relative antioxidant effectiveness of different isomers is originally believed to be in the order of a > b > c > d on the basis of hydrogen-donating power (Kamal-Eldin & Appelqvist, 1996). The corresponding tocopherols and tocotrienols are also expected to exert similar antioxidant potential due to the presence of the same chromanol group. How- ever, there is considerable conflicting evidence regarding their antioxidant activities in vivo, in vitro, in model systems, and in spe- cific food matrices (Eitenmiller & Lee, 2004; Kamal-Eldin & Appelqvist, 1996; Seppanen, Song, & Csallany, 2010). The reasons behind this confusion have not yet been fully understood. It is rec- ognized that the effectiveness of an antioxidant in foods is not only determined by its structure and chemical reactivity toward lipid radicals, but also dependent on other factors, including its stability, polarity, molecular size, concentration, environmental conditions (e.g., pH and temperature), physical distribution and mobility in http://dx.doi.org/10.1016/j.foodchem.2014.07.098 0308-8146/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +1 706 542 1067; fax: +1 706 542 1050. E-mail address: cakoh@uga.edu (C.C. Akoh). Food Chemistry 168 (2015) 504–511 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem