Growing environment (climate, rainfall, humidity, altitude)

Growing environment and climatic factors such as rainfall, humidity, the duration of sunlight, temperature, altitude and latitude have a significant effect on plant physiology, and consequently on composition of the fruit and the oil extracted (Conde

et al., 2008; Ripaet al., 2008; Ryan & Robards, 1998). These factors are also known to have influence on the development of taste and the aroma characteristics of olive oil. For example, dry climates with a lot of sunshine produce oil of good flavour and oils produced in dry seasons are characteristically sharp and bitter (Kiritsakis, 1998b).

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The impact of growing climate on composition and sensory attributes of VOO has been vigorously investigated (Aguileraet al., 2005; Aparicioet al., 1994; Breneset al., 1999; Criadoet al., 2004; Giacometti & Milin, 2001; Guerfelet al., 2009; Issaouiet al., 2010; Kricheneet al., 2009; Mousaet al., 1996; Zarrouket al., 2008). Criado et al.

(2004) reported significant quantitative differences (P<0.01) in a wide number of

phenolic compounds in VOO from ‘Arbequina’ variety growing in three different areas in Spain (Jaén, Lleida and Tarragona). The VOO obtained from Jaén grown at higher altitude (899 m above sea level) had significantly higher contents of hydroxytyrosol and tyrosol than oils from Tarragona growing at low altitude (between 400 and 450 m above sea level). Criado et al. (2004) suggested the higher levels of simple phenols could be related to more advanced maturation indexes of olive drupes in the olives from Jaén. On the other hand, Tarragona oils had significant concentration of secoiridoid derivatives, DHPEA-EDA and DHPEA-EA, which they attributed to the bitter sensory attribute and oxidative stability of the oil. The oils from Tarragona region also had the highest total phenolic content (between 92 and 111 mg/kg), oxidative stability (8.80 h) and the highest bitterness values (0.158). In another related study, (Mousaet al., 1996) found olives grown in lower altitudes (100 m above sea level) produced VOO with higher phenolic contents than from oils at higher altitude (800 m above sea level).

Lower altitude has a more suitable temperature and sunlight intensity leading to an increase of carbohydrate biosynthesis and acyl building blocks for polyphenol biosynthesis (Criadoet al., 2004; Kiritsakis, 1998a). It also follows that within the same growing area, as the temperature decreases (higher elevation) the percentage of unsaturated fatty acids increases (Mousaet al., 1996). However, a recent study on the main Tunisian cultivars, ‘Chemlali’ and ‘Chétoui’, cultivated in North and South Tunisia with different climatic conditions found higher total phenolic content in the oils obtained at higher altitude rather than lower altitude. Oils obtained from ‘Chemlali’ cultivated in the North (at an altitude of about 222 m) had 3 times greater phenol contents (573 mg/kg) than those in the same cultivar cultivated from the South (13 m) (173 mg/kg). A similar trend was obtained for ‘Chétoui’ in which the olive oil from the North had twice the phenols value (551 mg/kg), compared to the same oil from the South (274 mg/ kg). The oils from the North with higher phenolic content also had higher oxidative stability,

a finding similar to what other researchers have reported (Aguilera et al., 2005;

Aparicio et al., 1999). The high content of total phenolics and the secoiridoids, 3,4- DHPEA-EDA and 3,4-DHPEA-EA found in the VOOs at high altitude was similar to

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another recent study in Tunisia using VOO from the ‘Sigoise’ variety (Dabbou et al.,

2010a).

Another influence of growing environment on olive oil phenolics was illustrated by Aguilera et al. (2005) when they characterised ‘Frantoio’ and ‘Leccino’ virgin olive oil grown in two different locations, Mengibar in the open (280 m above sea level) and Cabra close to the hills (440 m above sea level), both locations in Andalusia, Spain. Their study found that the level of phenolics in both ‘Leccino’ and ‘Frantoio’ was hugely influenced by the growing environment with both cultivars responding in different ways; ‘Frantoio’ had a higher phenolic content in Cabra while ‘Leccino’ had a higher phenolic content in Mengibar. Sensorial characteristics also showed significant differences between the oils from each cultivar and location. Other than variation in phenolics, Aguilera et al. (2005) reported the oils at higher altitude, showed a greater content of oleic acid and higher stability, while from trees grown in the open the oils had higher tocopherol and linoleic acid contents.

The impact of growing environment seems to be more important for certain classes of phenolics and less important for others. Lignans and flavonoids have been reported as the group of phenolic compounds greatly affected by growing environment (Aparicio et al., 1994; Criado et al., 2004; Dabbou et al., 2009a; Giacometti & Milin, 2001; Morelloet al., 2006; Mousaet al., 1996; Tovaret al., 2001). Criado et al.(2004) found significant differences in the concentrations of flavonoids among the different growing regions, they obtained p-HPEA-EDA/lignans ratio of 1.4 in Lleida region olive oils whereas the ratio in oils from Jaén and Tarragona regions was 0.7. Lignans are thus suggested important for olive characterisation based on growing region and as a

varietal marker in VOO produced from different regions (Carrasco-Pancorbo et al.,

2006b; Criadoet al., 2004; Mulinacciet al., 2006; Oliveras-Lopezet al., 2007; Owenet al., 2000a). Vinhaet al.(2005) showed the impact of geographical location on phenolic composition in olives when they reported the phenolic profiles of Portuguese olive fruit using high performance liquid chromatography (HPLC). Their study found considerable variations in hydroxytyrosol, oleuropein and flavonoids in the olives obtained from different regions.

The above findings on the effect of growing environments on phenolic profiles have prompted the suggestion that phenolic profiles can potentially be used as markers

of geographical origins (Guerfel et al., 2009). Other authors have already suggested

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(Gomez-Alonso et al., 2002; Salvadoret al., 2003). These studies acknowledge that

climate and growing region has an impact on phenolic composition of VOO (Aguileraet

al., 2005; Aparicioet al., 1994; Criadoet al., 2004; Dabbouet al., 2009b; Giacometti & Milin, 2001; Guerfelet al., 2009; Mousaet al., 1996; Vinhaet al., 2005).