Comparative study on volatile compounds from Tunisian and Sicilian monovarietal virgin olive oils Olfa Baccouri a , Alessandra Bendini b, * , Lorenzo Cerretani b , Mokhtar Guerfel a , Béchir Baccouri a , Giovanni Lercker b , Mokhtar Zarrouk a , Douja Daoud Ben Miled a a Laboratoire Caractérisation et Qualité, de l’Huile d’Olive, Centre de Biotechnologie de Borj-Cédria, 901-2050 Hammam-Lif, Tunisia b Dipartimento di Scienze degli Alimenti, Università di Bologna, Piazza Goidanich 60, 47023 Cesena (FC), Italy article info Article history: Received 4 December 2007 Received in revised form 11 March 2008 Accepted 24 March 2008 Keywords: Virgin olive oil Volatile compounds Ripening Irrigation Headspace-solid-phase microextraction (HS–SPME) abstract The effects of ripening degree of olives on volatile profile of monovarietal virgin olive oils (VOO) from Tunisian and Sicilian cultivars were investigated. Fruits obtained from Tunisia (Chétoui and Chemlali) and Italy (Nocellara del Belice, Biancolilla and Cerasuola) were picked at three different stages of ripeness and then immediately processed. Moreover, the changes in volatile composition were evaluated in Chét- oui variety as a function of the irrigation regime versus the rain-fed control. Using headspace–solid-phase microextraction (HS–SPME) technique coupled to GC–MS and GC–FID, the volatile compounds of the monovarietal virgin olive oils were identified and quantitatively analyzed. The proportions of different classes of volatiles of oils showed significant differences throughout the maturity process. The results suggest that adding to the genetic factor; agronomic conditions affect the volatile formation and there- fore the organoleptic properties of VOO. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Virgin olive oil is a valuable vegetable oil, which is often used without any preliminary refining process (Olias, Perez, Rios, & Sanz, 1993). It is extracted from fresh and healthy olive fruits (Olea europeae L.) by mechanical or other physical methods (washing, decantation, centrifugation or filtration). These technological pro- cedures, if correctly adopted, are able to preserve the volatile and non-volatile compounds which are mainly responsible for fragrant and delicate flavour of virgin olive oil which is highly prized by consumers. The distinctive aroma of virgin olive oil is attributed to a large number of chemical compounds of different chemical classes, aldehydes, alcohols, esters, hydrocarbons, ketones, furans and, probably, other as yet unidentified volatile compounds (Kalua et al., 2007; Kiritsakis, Nanos, Polymenoupoulos, Thomai, & Sfaki- otakis, 1998; Vichi et al., 2003a). The volatile compounds of virgin olive oil do not contribute to its whole aroma with the same impor- tance and the high concentration volatile compounds do not neces- sarily serve as the major contributors of odour. Several chemical factors such as volatility, hydrophobic character, type and position of functional groups seem to be more related to the odour intensity of a volatile compound than its concentration. Therefore, the influ- ence of different volatile compounds must be evaluated not only on the basis of their concentration, but also on the basis of their odour thresholds, that play a key-role. Indeed, the compound’s odour threshold value is its minimum concentration able to give rise to an olfactory response. As an example, hexanal seems to con- tribute more to green odour than E-2-hexenal because of its lower odour threshold (75–300 vs. 420–1125 lg kg À1 )(Angerosa, 2002; Aparicio & Luna, 2002; Kalua et al., 2007; Morales, Luna, & Aparicio, 2005; Reiners & Grosch, 1998). From the biochemical point of view, the volatiles found in virgin olive oil are mainly produced in plant organs by the oxidation of fatty acids though intracellular biogenic pathways (Angerosa & Basti, 2001; Kalua et al., 2007). Some of these volatiles are present in the intact tissue of the fruit and others are formed during dis- ruption of cell structure during virgin olive oil production due to the enzymatic reactions in the presence of oxygen. It is generally agreed that endogenous plant enzymes, through the lipoxygenase pathway (LOX) are responsible for the positive aroma perceptions in olive oil, whereas chemical oxidation and exogenous enzymes, usually from microbial activity, are associated with sensory defects (Angerosa & Basti, 2001; Kalua et al., 2007; Morales, Alonso, Rios, & Aparicio, 1995; Morales, Rios, & Aparicio, 1997). The major volatile compounds responsible for odour notes of virgin olive oils are the C 6 and the C 5 volatile compounds coming from primary or second- ary LOX pathway, respectively (Angerosa, 2002; Aparicio & Mor- ales, 1998; Kiritsakis et al., 1998). Moreover, the presence of minor volatile compounds may provide useful quality markers 0308-8146/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2008.03.066 * Corresponding author. Tel.: +390 547338121; fax: +390 547382348. E-mail address: alessandra.bendini@unibo.it (A. Bendini). Food Chemistry 111 (2008) 322–328 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem