Original article Lipid stability in powdered infant formula stored at ambient temperatures Marı´a del Carmen Garcı ´a-Martı ´nez, 1 Luis M. Rodrı´guez-Alcala ´, 1 Susana Marmesat, 2 Leocadio Alonso, 3 Javier Fontecha 1 & Gloria Ma ´ rquez-Ruiz 1 * 1 Instituto del Frı´o (CSIC), 28040 Madrid, Spain 2 Instituto de la Grasa (CSIC), 41012 Sevilla, Spain 3 Instituto de Productos La´cteos de Asturias (CSIC), 33300 Villaviciosa, Asturias (Received 22 February 2010; Accepted in revised form 30 July 2010) Summary Lipid stability of standard infant formula was evaluated at ambient temperatures, namely 25, 30 and 37 °C, during 3 months. Lipids were thoroughly analysed to evaluate changes in fatty acid composition and trans fatty acid isomers, non-volatile oxidation compounds including oxidised, dimeric and polymeric triacylgly- cerols, and tocopherol. No significant changes in either of the parameters examined were found in total lipids extracted from infant formula along the storage period. However, the minor free oil fractions (about 7.5% of total lipids) showed a significant increase in oxidation compounds and marked decrease in tocopherol levels during storage at all temperatures. Samples stored at 37 °C for 3 months were rancid and, accordingly, contained the highest oxidation level in the free oil fraction, whereas total lipids extracted were apparently not oxidised. Results showed the necessity of analysing separately the free oil fraction in infant formulae to obtain a clear picture of the oxidation status. Keywords Free oil, infant formula, oxidation compounds, storage, tocopherol. Introduction Powdered infant formulae normally show fatty acid compositions similar to those of human milk, generally achieved by combination of vegetable oils such as sunflower, soybean, coconut, palm, high-oleic safflower, peanut, low-erucic acid rapeseed and corn oils (Nasir- pour et al., 2006). A number of formulations are nowadays supplemented with long-chain polyunsatu- rated fatty acids (LC-PUFA) as it has been reported that preterm and possibly new-born infants are not capable of synthesising sufficient amounts of such fatty acids to cover their needs for brain and retina develop- ment (Fleith & Clandinin, 2005). Also, vitamin and mineral fortification is necessary to fulfil nutritional requirements of infant formulae. As a consequence, infant formulae normally contain a relatively large amount of unsaturated, oxidisable fatty acids together with non-negligible amounts of prooxidant minerals, including iron, and hence it is essential to control lipid stability during storage to ensure their nutritional value and safety (Nasirpour et al., 2006). Changes in lipid oxidation parameters during storage of powdered infant formulae have been reported in a few studies (Angulo et al., 1998; Cha´vez-Servı´n et al., 2008a; De La Presa-Owens et al., 1995; Garcı´a-Llatas et al., 2006; Manglano et al., 2005; Michalski et al., 2008; Rodrı´guez-Alcala et al., 2007; Romeu-Nadal et al., 2007; Thomkinson & Mathur, 1990; Velasco et al., 2008) but the complexity of both the food matrix and the oxidation process usually leads to fluctuations or inconsistencies in oxidation measurements (De La Presa-Owens et al., 1995; Angulo et al., 1998; Manglano et al., 2005; Garcı´a-Llatas et al., 2006; Cha´vez-Servı´n et al., 2008a). Among the major causes for the confusing data obtained is the influence of the extraction proce- dures applied on the methods used for the analysis of oxidation, as occurs with peroxide value determination (Velasco et al., 2008). It is poorly known whether the changes in the lipid fraction during storage may occur within temperature ranges close to ambient conditions, including 25 °C as the usual room temperature in markets and food stores, and up to 30 and 37 °C, which can be reached in certain stores and houses during summer. In our previous work, lipid composition of conventional powdered infant formulae was thoroughly analysed during 4 years of *Correspondent: Fax: 34 915493627; e-mail: gmarquez@if.csic.es International Journal of Food Science and Technology 2010, 45, 2337–2344 2337 doi:10.1111/j.1365-2621.2010.02405.x Ó 2010 The Authors. International Journal of Food Science and Technology Ó 2010 Institute of Food Science and Technology