Headspace composition of cod liver oil and its evolution in storage after opening. First evidence of the presence of toxic aldehydes María D. Guillén a, * , Izaskun Carton a , Jesus Salmeron b , Carmen Casas b a Tecnología de Alimentos, Facultad de Farmacia, UPV/EHU, Paseo de la Universidad No. 7, 01006 Vitoria-Gasteiz, Spain b Nutrición y Bromatología, Facultad de Farmacia, UPV/EHU, Paseo de la Universidad No. 7, 01006 Vitoria-Gasteiz, Spain article info Article history: Received 18 April 2008 Received in revised form 26 September 2008 Accepted 3 November 2008 Keywords: Cod liver oil Headspace components Storage Solid phase microextraction Gas chromatography/mass spectrometry 4-Hydroxy-(E)-2-hexenal 4-Hydroperoxy-(E)-2-hexenal 4-Oxo-(E)-2-hexenal 4,5-Epoxy-heptenal abstract The headspaces of two samples of cod liver oil, when recently acquired, after five and after fifteen months from opening, were studied by solid phase microextraction, followed by gas chromatography/mass spec- trometry. Nearly one hundred compounds were found, some of them identified for the first time as cod liver oil components. In both samples, the presence of the toxic 4-hydroxy-(E)-2-hexenal and of 4-oxo- (E)-2-hexenal was detected, as well as that 4,5-epoxy-2-heptenal in one of the samples; this is the first time that these toxic compounds have been described as being present in cod liver oil. In the early oxi- dation stages, taking place during storage, the compounds formed are mainly of low molecular weight; some of these could be adopted as oxidation markers of cod liver oil. The possibilities of using the tech- nique to evaluate the oxidation level of cod liver oil are shown. These results suggest the need to monitor the levels of toxic oxygenated a,b-unsaturated aldehydes in cod liver oil in order to ensure its safety. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Cod liver oil has been widely used, for centuries, to treat and prevent rickets in children, and in recent years its consumption has increased considerably because of its health benefits (Brox et al., 2001; Gruenwald, Graubaum, & Harde, 2002; Knight, Leso- sky, Barnett, Raboud, & Vieth, 2007; Raeder, Steen, Vollset, & Bjel- land, 2007; Shimokawa, 2001) and its contents of omega-3 acyl groups and vitamins A and D (Whiting & Calvo, 2005). However, it has also been indicated that excessive consumption of this oil involves risks, associated not only with overdoses of A and D vitamins, but also with the intake of potential toxic com- pounds which may be present in cod liver oil; amongst these, poly- chlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), or heavy metals, such as mercury, cadmium and lead, have been cited (Guallar et al., 2002; Storelli, Storelli, & Marcotri- giano, 2004). In addition, the presence of toxic compounds, result- ing from oxidation, is also possible. To prevent this latter problem, the values of some parameters, such as peroxide and anisidine val- ues, must be in agreement with supplement regulations (European Pharmacopoeia, 2003). However, the determination of the oxida- tion level of fish oil, using these classical methods, does not always give satisfactory results (Connell, 1990). Despite the long tradition and increasing current trend in its consumption, there are only two previous studies of the volatile components of cod liver oil (Karahadian & Lindsay, 1989; Olsen, Vogt, Saarem, Greibrokk, & Nilsson, 2005). They each concern the dynamic headspace composition of one sample of commercial cod liver oil. In one of them, 48 compounds were identified (Karahadian & Lindsay, 1989) and in the other, 29 (Olsen et al., 2005); in the latter the efficiency of some antioxidants in prevent- ing oxidation of the oil was also studied. By contrast, the headspace composition of unoxidised or oxidised vegetable oils (Guillén, Cabo, Ibargoitia, & Ruiz, 2005; Guillén & Goicoechea, 2008a), and of oil in water emulsions (Bonoli-Carbognin, Cerretani, Bendini, Almajano, & Gordon, 2008), have received more attention. A study of the static headspace of two samples of commercial cod liver oil is now carried out by solid phase microextraction (SPME), followed by gas chromatography/mass spectrometry (GC/MS). The aim of this study is to find whether the technique can provide new information about this dietetic supplement in relation to volatile components, amongst which are those respon- sible for odour and aroma, and/or potential toxic compounds. In addition, the changes in the headspace composition of these oils, with five and fifteen months of storage after opening the bottle, 0308-8146/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2008.11.007 * Corresponding author. Tel.: +34 945 013081; fax: +34 945 013014. E-mail address: mariadolores.guillen@ehu.es (M.D. Guillén). Food Chemistry 114 (2009) 1291–1300 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem