**2. Flavours and off-flavours of virgin olive oil: The molecules responsible for sensory perceptions**

VOOs are defined by the European Community as those "…oils obtained from the fruit of the olive tree solely by mechanical or other physical means under conditions that do not lead to alteration in the oil…" (EEC Reg. 2568/91). This production method renders VOO different from other vegetable oils that undergo refining, which leads to loss of most of the minor components such as volatile molecules and "polar" phenolic compounds.

Many authors (Angerosa et al., 2004; Kalua et al., 2007) have clarified that several variables affect the sensory characteristics and chemical composition of an EVOO. These include environmental factors, cultivation and agronomic techniques, genetic factors (cultivar), ripening degree of drupes, harvesting, transport and storage systems of olives, processing techniques, storage and packaging conditions of the oil.

The sensory attributes of EVOO mainly depend on the content of minor components, such as phenolic and volatile compounds. The independent odours and tastes of different volatile and phenolic compounds that contribute to various and typical EVOO flavours have been extensively studied; the sensory and chemical parameters of EVOO have been correlated in a large number of investigations (Bendini et al., 2007; Cerretani et al., 2008).

Each single component can contribute to different sensory perceptions. It is well established that specific phenolic compounds are responsible for bitterness and pungency (Andrewes et al., 2003; Gutiérrez-Rosales et al., 2003; Mateos et al., 2004). Few individuals, except for trained tasters of EVOO, know that the bitterness and pungency perceived are considered positive attributes. These two sensory characteristics, more intense in oils produced from olives at the start of crop year, are strictly related to the quali-quantitative phenolic profile of EVOO.

Even in small quantities, phenols are fundamental for protecting triacylglycerols from oxidation. Several authors (Gallina Toschi et al., 2005, Carrasco-Pancorbo et al., 2005; Bendini et al., 2006; Bendini et al., 2007) have reported their importance as antioxidants as well as nutracetical components. The major phenolic compounds identified and quantified in olive oil belong to five different classes: phenolic acids (especially derivatives of benzoic and cinnamic acids), flavones (luteolin and apigenin), lignans ((+)-pinoresinol and (+)-

Positive or negative sensory descriptors of VOO have been related to volatile and phenol

The characteristic taste of VOO, and in particular some positive attributes such as bitterness and pungency that are related to important health benefits, is not completely understood or appreciated by consumers. In this respect, it is interesting to consider the degree of acceptability of VOO in several countries based on literature data. In this way, it is possible to lay the foundations for correct instruction of the sensory characteristics of EVOO. The main chemical, biochemical and technological processes responsible for the positive and negative (defects) descriptors of VOO are summarized in this chapter. An overview on the sensory methodologies proposed, applied and modified during the last 20 years is also

**2. Flavours and off-flavours of virgin olive oil: The molecules responsible for** 

VOOs are defined by the European Community as those "…oils obtained from the fruit of the olive tree solely by mechanical or other physical means under conditions that do not lead to alteration in the oil…" (EEC Reg. 2568/91). This production method renders VOO different from other vegetable oils that undergo refining, which leads to loss of most of the

Many authors (Angerosa et al., 2004; Kalua et al., 2007) have clarified that several variables affect the sensory characteristics and chemical composition of an EVOO. These include environmental factors, cultivation and agronomic techniques, genetic factors (cultivar), ripening degree of drupes, harvesting, transport and storage systems of olives, processing

The sensory attributes of EVOO mainly depend on the content of minor components, such as phenolic and volatile compounds. The independent odours and tastes of different volatile and phenolic compounds that contribute to various and typical EVOO flavours have been extensively studied; the sensory and chemical parameters of EVOO have been correlated in

Each single component can contribute to different sensory perceptions. It is well established that specific phenolic compounds are responsible for bitterness and pungency (Andrewes et al., 2003; Gutiérrez-Rosales et al., 2003; Mateos et al., 2004). Few individuals, except for trained tasters of EVOO, know that the bitterness and pungency perceived are considered positive attributes. These two sensory characteristics, more intense in oils produced from olives at the start of crop year, are strictly related to the quali-quantitative phenolic profile of

Even in small quantities, phenols are fundamental for protecting triacylglycerols from oxidation. Several authors (Gallina Toschi et al., 2005, Carrasco-Pancorbo et al., 2005; Bendini et al., 2006; Bendini et al., 2007) have reported their importance as antioxidants as well as nutracetical components. The major phenolic compounds identified and quantified in olive oil belong to five different classes: phenolic acids (especially derivatives of benzoic and cinnamic acids), flavones (luteolin and apigenin), lignans ((+)-pinoresinol and (+)-

minor components such as volatile molecules and "polar" phenolic compounds.

a large number of investigations (Bendini et al., 2007; Cerretani et al., 2008).

techniques, storage and packaging conditions of the oil.

profiles, which are responsible for aroma and taste, respectively.

presented.

EVOO.

**sensory perceptions** 

acetoxypinoresinol), phenyl-ethyl alcohols (hydroxytyrosol, tyrosol) and secoiridoids (aglycon derivatives of oleuropein and ligstroside). The latter are characteristic of EVOOs.

Several investigations (Gutiérrez-Rosales et al., 2003; Mateos et al., 2004) have demonstrated that some phenols, and in particular secoiridoid derivatives of hydroxytyrosol, are the main contributors to the bitterness of olive oil; other phenolic molecules such as decarboxymethyl-ligstroside aglycone, which seems to be a key source of the burning sensation, can stimulate the free endings of the trigeminal nerve located in the palate and gustative buds giving rise to the chemesthetic perceptions of pungency and astringency (Andrewes et al., 2003). Using a trained olive oil sensory panel, some investigators (Sinesio et al., 2005) have studied the temporal perception of bitterness and pungency with a time-intensity (TI) evaluation technique. It has been shown that the bitterness curves had a faster rate of increase and decline than the pungency curves. It was also demonstrated that differences in kinetic perception are linked to the slower signal transmission of thermal nociceptors compared to other neurons.

On the other hand, approximately 180 compounds belonging to several chemical classes (aldehydes, alcohols, esters, ketones, hydrocarbons, acids) have been separated from the volatile fractions of EVOOs of different quality. Typical flavours and off-flavour compounds that affect the volatile fraction of an oil obtained from olives originate by different mechanisms: positive odours are due to molecules that are produced enzymatically by the so-called lipoxygenase (LOX) pathway. Specifically both C6 aldehydes, alcohols and their corresponding esters and minor amounts of C5 carbonyl compounds, alcohols and pentene dimers are responsible for pleasant notes. In contrast, the main defects or off-flavours are due to sugar fermentation (*winey*), amino acid (leucine, isoleucine, and valine) conversion (*fusty*), enzymatic activities of moulds (*musty*) or anaerobic microorganisms (*muddy*), and to auto-oxidative processes (*rancid*).

Volatile molecules can be perceived in very small amounts (micrograms per kilogram or ppb) and these compounds do not have the same contribution to the global aroma of EVOO; in fact, their influence must be evaluated not only on the basis of concentration, but also on their sensory threshold values (Angerosa et al., 2004; Kalua et al., 2007). In addition, antagonism and/or synergism among different molecules can occur, affecting the global flavour of EVOO. Chemical factors of molecules (volatility, hydrophobic character, size, shape, conformational structure), type and position of functional groups appear to affect the odour and taste intensity more than their concentration due to their importance in establishing bonds with receptor proteins (Angerosa et al., 2004).

In general, it is correct to surmise that from healthy olives, picked at the right degree of ripening and properly processed, it is always possible to obtain an EVOO, independent of the olive variety. However, from unhealthy olives or from those harvested off the ground it is inevitable to produce an olive oil characterized by unpleasant flavours and sensory defects. Thus, both natural (olive variety, environmental conditions, degree of ripening and health status of olives) and extrinsic (technological processing by olive farmer/mill worker) factors may profoundly influence olfactory and gustative notes.

Several agronomic and climatic parameters can affect the volatile and phenolic composition of VOOs. The genetic characteristics of the olive cultivar are some of the most important

Sensory Analysis of Virgin Olive Oil 113

in extraction of phenolic compounds due to more intense tissue breaking; therefore, a more vigorous milling system should be used to process olive varieties that are naturally low in phenolic compounds, and permit enrichment of bitter and pungency intensities. The use of more violent milling systems also produces a significant increase in olive paste temperature and a corresponding decrease of the activity of enzymes that play a key role in the production of volatile compounds responsible for fruity and other green notes (Salas &

Concerning the malaxation phase, which consists in a slow kneading of the olive paste, the time-temperature pair should be carefully controlled to obtain a high quality EVOO. The lipoxygenase pathway is triggered by milling of olives and is active during malaxation. The volatile compounds produced are incorporated into the oil phase to confer its characteristic aroma. Specifically, a temperature above 28°C for more than 45 min should be avoided; in fact, these conditions can lead to the deactivation of enzymes that produce both positive volatile compounds and oxidize the phenolic compounds causing changes in oil flavour (Salas & Sanchez 1999; Kalua et al., 2007). The reduced concentration of oxygen in paste, obtained by replacing air with nitrogen in the headspace of malaxer during processing, can inhibit these enzymes and minimize the oxidative degradation of phenolic compounds during processing (Servili et al., 1999; Servili et al., 2003). Malaxation under erroneous conditions is responsible for the unpleasant flavor known as a "*heated defect*" due to the

One of the main disadvantages of discontinuous mill systems is the possible fermentation and/or degradation phenomena of residues of pulp and vegetation waters on filtering diaphragms; these reactions give rise to a defect termed "*pressing mats*", but also promote winey and fusty defects (Angerosa et al., 2004). It is well known that among continuous systems, discontinuous mill systems with a three-phase decanter need lukewarm water to dilute olive paste in contrast to a two-phase decanter, which has two exits producing oil and pomace and separates the oil phase from the olive paste This latter system has advantages in terms of water reduction and major transfer of phenols from the olive paste to the oil, with a

The amount of water added determines the dilution of the aqueous phase and lowers the concentration of phenolic substances that are more soluble in vegetable waste water. Consequently, a large amount of antioxidants is lost with the wastewater during processing. In addition to phenolic compounds, some volatile compounds accumulate more in oil from a dual-phase decanter than in oils extracted with three-phase decanters. Therefore, the use of a two-phase decanter promotes greater accumulation of volatile and phenolic compounds that are not lost in the additional water as in a three phase decanter. The higher concentrations of these compounds are related to the high intensities of bitter, pungent, green fruity, freshly cut lawn, almond and tomato perceptions (Angerosa et al., 2000;

In unfiltered oil, the low amounts of sugars or proteins that remain for extended times in oil can be fermented or degraded by specific anaerobic microrganisms of the *Clostridium* genus,

formation of specific volatile compounds (Angerosa et al., 2004).

consequent increase in oxidative stability, bitterness and pungency.

The application of different oil separation systems

Angerosa et al., 2004; Kalua et al., 2007).

Storage of oil under suitable conditions

Sanchez, 1999; Servili et al., 2002).

aspects that determine the level of enzymes in fruit (Angerosa et al., 1999) that are involved in synthesis of volatile molecules (LOX pathway) and phenol compounds (biosynthetic pathways via PPO and -glucosidase) present in VOOs.

Even if enzymatic activity depends on the stage of ripeness (Morales et al., 1996; Aparicio & Morales 1998) agronomic (fertilization, irrigation) and climatic (temperature and rainfall) conditions also play an important role.
