Characterization of 3,4-DHPEA-EDA oxidation products in virgin olive oil by high performance liquid chromatography coupled with mass spectrometry Ilona Di Maio, Sonia Esposto, Agnese Taticchi, Roberto Selvaggini, Gianluca Veneziani, Stefania Urbani, Maurizio Servili ⇑ Dipartimento di Scienze Economico-Estimative e degli Alimenti, Sezione di Tecnologie e Biotecnologie degli Alimenti, Università degli Studi di Perugia, Via S. Costanzo, 06126 Perugia, Italy article info Article history: Received 2 July 2012 Received in revised form 3 October 2012 Accepted 10 October 2012 Available online 10 November 2012 Keywords: Virgin olive oil Hydrophilic phenols Secoiridoids Oxidation Antioxidants abstract Secoiridoid derivatives are the most important antioxidants of virgin olive oil (VOO), and their oxidation products could be used as molecular markers of VOO freshness to define the VOO autoxidation state. The aim of this research was to characterise the dialdehydic form of decarboxymethyl elenolic acid linked to hydroxytyrosol (3,4-DHPEA-EDA) oxidation products to find analytical indicators that could be used as early evaluation index of the VOO autoxidation state. 3,4-DHPEA-EDA was oxidised by enzymatic and Fenton reactions. Terpenic structure oxidation products accumulated in VOO during the autoxidation process, thus they may be used as early evaluation index of the VOO autoxidation state before fatty acids oxidation. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Virgin olive oil (VOO) is one of the principal components of the Mediterranean diet with its chemical composition contributing to daily requirements of monounsaturated fatty acids and vitamin E (Frankel, 2011). Moreover, VOO supplies specific antioxidants rep- resented by hydrophilic phenols such as phenolic alcohols and acid, flavonoids, lignans and secoiridoids (Brenes et al., 2000; Montedoro, Servili, Baldioli, & Miniati, 1992a; Obied, Karuso, Prenzler, & Robards, 2007; Owen et al., 2000b; Rovellini, Cortesi, & Fedeli, 1997). The presence of hydrophilic phenols in VOO is a fundamental aspect of its quality that is closely related to many specific functions of these compounds (Baldioli, Servili, Perretti, & Montedoro, 1996; Brenes, García, García, & Garrido, 2001; Servili et al., 2009). VOO hydrophilic phenols are involved in important biological activities that have both clinical and nutritional effects (Cornwell & Ma, 2008; Mangas-Cruz et al., 2004; Owen et al., 2000a; Servili et al., 2009). VOO phenolic antioxidants have bene- ficial effects to contrast several chronic and degenerative diseases, such as inflammatory diseases, cardiovascular diseases and cancer (Fabiani et al., 2011; Frankel, 2011; Orlando, 2002). In addition, these antioxidants have an important protective action in food by delaying the autoxidation of VOO, thus having a beneficial effect on the shelf-life of olive oil (Baldioli et al., 1996; Carrasco-Pancorbo et al., 2005; Gallina-Toschi, Cerretani, Bendini, Bonoli-Carbognin, & Lercker, 2005; Obied, Prenzler, & Robards, 2008a; Shahidi & Wanasundara, 1997). Experimental results have shown that VOO oxidative stability is principally due to oleuropein derivatives, such as the dialdehydic form of decarboxymethyl elenolic acid linked to hydroxytyrosol (3,4-DHPEA-EDA) and an isomer of oleuropein aglycone (3,4-DHPEA-EA), and that other components, such as lignans and ligstroside derivatives, have a marginal role in VOO oxidation stability (Carrasco-Pancorbo et al., 2005; Obied et al., 2008b). 3,4-DHPEA-EDA and 3,4-DHPEA-EA belong to the class of secoiridoids, they are characterised by the presence elenolic acid or its derivatives in their molecular structure (Montedoro et al., 1993; Owen et al., 2000b; Servili et al., 1999). Secoiridoids and hydroxytyrosol (3,4-DHPEA) are the strongest natural antioxidant of VOO (Baldioli et al., 1996; Brenes et al., 2001). VOO secoiridoids are affected by enzymatic oxidation during the oil mechanical extraction process due to the activation of enzymes, such as poly- phenol oxidase and peroxidase (Servili et al., 2007). During storage, both hydrolytic and oxidative nonenzymatic process can take place. Over time, there is a decrease in VOO secoiridoid content and an increase in simple phenols (such as tyrosol and hydroxyty- rosol), elenolic acid, oxidised forms of elenolic acid and oxidised forms of secoiridoids (Brenes et al., 2001; Lerma-García, Herrero- Martínez, Simó-Alfonso, Lercker, & Cerretani, 2009; Rovellini & Cortesi, 2002). It is important to study the degradation chemistry of antioxidant compounds during VOO autoxidation to understand the antioxidant actions as well as the synergistic effects of 0308-8146/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2012.10.097 ⇑ Corresponding author. Tel.: +39 075 5857942; fax: +39 075 5857916. E-mail address: servimau@unipg.it (M. Servili). Food Chemistry 138 (2013) 1381–1391 Contents lists available at SciVerse ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem