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Main Geographical features
Lebanon is a home to the oldest olive trees dating back centuries (at least 1,500 years). It has been renowned for its trade in crop products including olive and olive oil along the Mediterranean Basin (Mahfoud, 2007; Beayno et al., 2002; Thalman, 2000). The country’s topography consists of a coast and two mountains running in parallel and separated by an agricultural plateau called Bekaa. Although landscape variations may give a rise to differentiated climatic conditions, Lebanon is characterized by a moderate Mediterranean climate where the average rainfall of 2.2 billion cubic meter per year allows the growth of olive trees.
Olive trees, mainly rain fed, cover approximately 5.4 % of the Lebanese territory or 8 % of total agricultural lands in Lebanon. Olive groves are dispersed over the main five territories of Lebanon: North, Nabatiyeh, South, Bekaa and Mount Lebanon covering a range of altitude from 45 to 900 m above sea level (Figure 3) (IDAL, 2017b). The Lebanese olive germplasm is characterized by a high level of diversity. Five local varieties, namely, Aayrouni, Abou-Chawki, Baladi, Del and Soury, are the most cultivated in commercial plantations used for both oil and table olives (Table 4). The Soury variety is the most cultivated variety where it occupies 85% of the cultivation areas. It originated from Tyr, and it is used for both table olive and oil production (Chehade et al., 2016).
Imports and exports
Lebanese olive oil holds the highest commercial prospects amongst all the other crops covering about 21% of the total cultivated area and 69% of the land cultivated with fruits. Although Lebanon is considered a small-scale producer of olive oil as compared to other Mediterranean countries, it has the reputation of producing high-quality artisanal oils. Exports of Lebanese olive has been increasing since 2006 at a rate of 15 % in value each year (Figure 5) especially to the gulf region and United States. For instance, Lebanon exported about 904 t of olive oil in 2005 to GCC market, whereas in 2016, 13,587 t was exported to GCC. Although a substantial reduction was noted in exports in 2017, a clear tendency of increase in Lebanese olive oil shows the ability of producers to infiltrate the export market (IDAL, 2017b).
Fluctuation of EVOO/VOO components due to factors of different origins
A complex interaction exists between genetics, technological and agronomical factors (climate, soil, year, irrigation, growing area, fruit maturity) and the chemical composition of olive oil. Each of one of these factors and sub-factors affect oils’ characteristics in its own manner.
Agronomical variables
The choice of which cultivar to grow is one of the most important decisions and the following factors should be taken into consideration before selection:
• Tree vigor, alternate bearing, maturity index, oil content and extractability.
• Orchard profitability (olive oil yield).
• Environmental factors (resistance to drought, cold hardiness…).
• Market demand.
• Production costs.
• Chemical composition.
Each cultivar has its own chemical fingerprint. The triglyceride structure of olive oil is unique for each cultivar. For instance, 73 of the world’s most common cultivars were compared and differences in the fatty acid content were found. For example, palmitic fatty acid percent ranged from 8.49 to 16.46, palmitoleic from 0.41 to 2.26, stearic from 1.46 to 3.79, oleic from 56.12 to 78.34, linoleic from 4.44 to 13.34 (Lombardo et al., 2008; Mannina et al., 2003; Zarrouk et al., 2009)
Minor components such as sterols and polyphenols are also highly influenced by the cultivar. The polyphenol content of olive oil varies from 182 to 1240 ppm depending on the cultivar as long as the olives and the extraction process are in excellent conditions and following good manufacturing processes guidelines (García-González et al., 2010; Tura et al., 2007). As for sterols, it constitutes the majority of the unsaponifiable fraction where an increased interest in the latter has been noticed due to its importance in the quality regulation of olive oil. Each cultivar has its own fingerprint represented by the sterol profile. A study by Kyçyk et al. (2016) showed that each of the 43 olive cultivars has their own distinct sterol profile. Because of this variability, sterols can be used as a discrimination tool among monovarietal VOOs. It can also be used in olive breeding projects to obtain new olive cultivars with improved sterol fraction.
Climate and elevation
Olive oil is mainly composed of fatty acids, especially monounsaturated fatty acids (oleic acids) in addition to polyunsaturated fatty acids like linoleic and linolenic (Salvador et al., 2003). The fatty acids profile of oils produced from the same cultivar is the same in oils produced in similar climates and growing conditions. However, a difference in the climate or altitude between regions has led to cases where large differences have been observed in the fatty acids composition of oil (Aparicio et al., 1994). Çetinkaya et al. (2017) have found that a difference in altitude has an effect on oleic acid, palmitic acid, linoleic acid and stearic acid. Other authors like Nergiz and Ergönül (2009) also found out that olives planted in high-altitude locations are rich in monounsaturated fatty acids (MUFA), while olives planted in low-altitude locations are rich in saturated fatty acids (SFA).
Furthermore, the change in altitude correspond to a decrease or increase in the environment temperature, relative humidity and thus the modification of the underlying physiological metabolic processes at the level of olive fruit, in particular, the process of fatty acid synthesis. Oleate desaturase, an enzyme responsible for desaturation of Oleoyl-ACP (precursor of longer-chain unsaturated fatty acids) into linoleate-ACP might be the reason behind the notable difference in the MUFA and PUFA concentrations between these two groups. This enzyme has been extensively discussed in seed oils. In sunflower seed, the low temperature lead to the activation of the desaturase enzymes and the level of desaturated fatty acids such as linoleic acid increase as a mechanism to tolerate low temperatures during pod filling. However, at high temperatures (30 oC), desaturases enzymes are partially and reversibly inhibited reducing the linoleic acid content in the oil. This mechanism, known in sunflower, and the information regarding the desaturase enzymes responses to change in climatic conditions in olive is limited (Hernandez et al., 2011) Several studies reported that the gradual decrease in temperature from October to January, as olive ripening advances, may increase the linoleic acid content in the olive fruit (Inglese et al., 2011; Gutiérrez et al., 1999). In addition, García-Inza et al. (2014) studied the effect of high temperature especially at the beginning of oil accumulation, by placing fruiting branches in transparent plastic chambers with individualized temperature control. The results showed that high temperatures could decrease the oleic acid content and increase palmitic, palmitoleic, linoleic, and linoleic acid. Micro-components also are affected by the climatic conditions. Several studies have shown that oil produced in warm coastal areas has fewer total polyphenols than those grown at higher altitudes and lower temperature regions (Osman, 1994). Sterols on the other hand are mostly related to fruit maturity and cultivar.
Fruit maturity
The effect of fruit maturity on olive oil chemical composition is significant. As olive fruit matures, the color of the fruit shifts from green at the beginning of the harvest period to small reddish-green spots to purple and lastly to black at the end of the harvest period (Motilva & Romero, 2010). Each stage imparts chemical variations on the level of metabolic processes of several compounds such as triglycerides, fatty acids, polyphenols, sterols and chlorophylls, which in turn have an impact on olive oil quality (Gargouri et al., 2016). These variations not only influence the quality but also the nutritional and organoleptic characteristics and the oxidative stability of olive oil (Maaitah et al., 2009). For instance, polyphenols and chlorophyll content decrease as fruit maturity increase especially when the olive fruit turns completely into black (last stage of fruit maturation).
As for fatty acids, Issaoui et al. (2010) related the increase in polyunsaturated fatty acids with fruit maturation. This is mainly due to continuing biosynthesis of triglycerides and to the actively desaturation of oleic acid into linoleic by oleate desaturase as the fruit ripens.
However, the variation based on the fruit maturity somehow depends on the cultivar. In some cases, the level of monosaturated fatty acids increases, whereas the level of saturated and polyunsaturated fatty acids increased as in the case of Barnea variety. Conversely, the delay of harvest has a detrimental effect on the quality of olive oil especially on the most widely spread cultivar in Lebanon, the Souri variety. Lodolini et al. (2017) have reported that the latter variety should be harvested early. As it ripens, oleic content declines and linoleic increases, quality indices especially free fatty acids are negatively affected, while polyphenol levels and oxidative stability drop sharply (Noorali et al., 2014). Also, it has been reported that the sterol content decreases sharply from 2850 g/kg to 1644 g/kg. Moreover, fruit maturation has also been shown to affect olive oil quality parameters such as free fatty acids, peroxide value, specific UV absorbances and sensory attributes (Dag et al., 2011; Famiani et al., 2002b; Gomez et al., 2011; Lazzez et al., 2008; Mailer et al., 2010; Varzakas et al., 2010).
Several methods have been recommended to determine the exact or ideal harvest time with respect to the quantity and quality of olive oil. These methods have been developed using organic acids such as malic and citric ratio (Donaire et al., 1975), degree brix (Migliorini et al., 2011), sugars such as mannitol (Marsilio et al., 2001), fruit respiration (Ranalli et al., 1998) or dry matter (Mickelbart & James, 2003). Other methods have related a connection between fruit maturity and specific fatty acids and sterols present in the pulp. However, the most common used method to determine fruit maturity, recommended by IOC, is the measurement of the fruit external and internal colors allowing the calculation of maturity index.
Fluorescence spectroscopy
Fluorescence spectroscopy has been successfully used as a rapid, non-invasive and highly sensitive technique for analysis of olive oil quality and showed to be more cost-efficient compared to other analytical procedures (Lleo et al., 2016). This type of spectroscopy can be particularly useful as routine quality control since the analysis is carried out directly on the intact samples without any pre-treatment or usage of chemical reagents (Sikorska et al., 2004). These advantages have rendered front face fluorescence as an important tool in the evaluation of olive oils properties. So, what is fluorescence? In simple words, it is a phenomenon resulting from the emission of light by the matter after absorption of light. Upon absorption of light in the UV or Vis range, the analyte absorbs a photon or is activated and reaches a higher energy level called the excited state. Jablonski’s diagram (Figure 8), is often used to illustrate the processes occurring between absorption and emission of light (Szudy & Toruniu, 1998). Based on this diagram, a molecule resting at the ground state absorbs energy at an excitation wavelength (that is specific property to the molecule itself), and it gets excited. This will gradually transfer the molecule to a one or higher energy levels (S1). The next stage will be vibrational relaxation which permits the electron to return to its lowest energy level, from S1 to S0 (ground state).
The return to the ground state emits a photon, at a wavelength higher than that of the excitation state, thus producing the fluorescence phenomenon. This phenomenon which is called fluorescence takes about a few picoseconds or even a few nanoseconds. The only limitation to this phenomenon, is that it only works with fluorophore compounds mainly those consisting of aromatic molecules or into those having enough electronic density (high conjugated chemical structure).
Table of contents :
Chapter 1: Literature Review
1. A general overview on olive oil
1.1. Olive oil: an introduction
1.2. Geographic distribution of olive oil production and consumption
1.3. The rise of regulation
1.4. Chemical Composition
1.4.1. Fatty acids
1.4.2. Sterols
1.4.3. Polyphenols
1.4.4. Chlorophylls
1.4.5 Aromatic compounds
2. Lebanese olive oil sector overview
2.1. Main Geographical features
2.2. Olive oil production
2.3 Imports and exports
3. Fluctuation of EVOO/VOO components due to factors of different origins
3.1. Agronomical variables
3.1.2. Climate and elevation
3.1.3 Fruit maturity
3.1.4 Other agronomical factors
3.2. Technological variables
3.2.1. Olive transport and storage
3.2.2. Processing methods
3.2.3. Storage conditions
4. Rapid & non-destructive analysis techniques
4.1. Spectroscopy
4.1.1 Fluorescence spectroscopy
4.1.2. Fluorescence spectra
4.1.3. Application of fluorescence in olive oil analysis
4.2. Flash GC
4.2.1. Sampling
4.2.2. Chromatographic separation
4.2.3 Sensory and chemical characterization
5. Chemometrics
5.1 Principal component analysis
5.2 Parallel factor analysis
5.3 Independent components analysis
5.3 Regression
Chapter 2: Materials and Methods
1. Sampling
1.1. Olive fruit and oil sampling
1.2. Olive fruit sampling technique
1.3. Olive oil extraction
2. Conventional chemical analysis of olive oil
2.1. Quality Indices
2.1.1. Acidity
2.1.2. Peroxide value
2.1.3. UV spectrophotometric investigation
2.2. Pigments in olive oil
2.2.1. Total chlorophylls and β-carotene
2.2.2. Total polyphenols
2.3. Fatty acids analysis
2.3.1. Preparation of the fatty acid methyl esters from olive oil (acid value ≤ 2.0 %)
2.3.2. Preparation of the fatty acid methyl esters from olive oil (acid value > 2.0 %)
2.3.3. Analysis of FAME by GC-FID
2.3.4. Method of calculation
2.4. Sterol analysis
2.4.1. Preparation of the unsaponifiable matter
2.4.2. Preparation of the basic thin layer chromatography plates
2.4.3. Preparation of the trimethylsilyl ethers
2.4.4. Sterol analysis by GC-MS
2.4.5. Method of calculation
3. Rapid techniques for olive oil analysis
3.1. 3D front-face fluorescence spectroscopy
3.2. Flash-GC
4. Chemometrics prerequisites
4.1 Notation
4.2 Three-way arrays
4.3 Preprocessing
4.3.1. Unfolding
4.3.2. Scaling
4.3.3. Rayleigh scatter
4.3.4. Warping for chromatographic signal alignment (GC-FID)
4.3.5. Outlier detection
Chapter 3: Impact of Growing Area and Technological Aspects on Lebanese Olive Oil: Characterization by unsupervised methods
Chapter 4: Conventional and Ultra-fast Analysis Exposing the Harvest Date Impact on Lebanese Olive Oil: The Soury Variety
Chapter 5: Does Variability Affect the Performance of Front-Face Fluorescence Spectroscopy? A Study Case on Commercial Lebanese Olive Oil
Chapter 6: General Results and Discussion
1. Results
1.1. Impact of growing area and technological aspects on Lebanese olive oil
1.2 Harvest Date effect on the Lebanese Olive Oil from the Soury Variety
1.3 A rapid technique replacing the conventional analytical methods
2. Discussion
Conclusion & Perspectives
References .
