Olive oil is the primary source of fat in the Mediterranean diet. Its consuming has been associated with a reduced risk of overall and cardiovascular mortality, cancer frequency, incidence of Parkinson and Alzheimer disease, leading to an improved life quality (Covas, Konstantinidou, & FitÙŽo, 2009).
Virgin olive oil is obtained from the fruit of the olive tree (Olea europaea L.) solely by mechanical or other physical means under conditions, particularly thermal conditions, that do not lead to alteration in the oil (Codex Alimentarius Commission, 2009; International Olive Oil Council, 2009). Pressing, centrifugation and percolation are usual methods for extraction of olive oil. Properly extracted olive oil from fruits with good quality can be consumed in the crude form, conserving the healthy components of the fruit.
World-wide production of olive oil during the last 20 years increased by almost 70% (from 1.7 to 2.8 million tons) (Zampounis, 2006). Olive oils make up a small proportion (<3.5%) of the volume in the world vegetable oil market. However, in terms of product value, olive oil has a 15% share of world trade (Luchetti, 2000). The price of olive oil can be two to five times higher than that of other vegetable oils depending on the country, category of the oil, and year (Luchetti, 2000).
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The authenticity of olive oil is an important issue from a commercial and health point of view (Garcia-Gonzalez, Aparicio-Ruiz, & Aparicio, 2008). Fraudulent addition of cheaper oils to extra virgin olive oil (EVOO), for example, can bring on the paradigm of the ''toxic oil syndrome", caused by the consumption of olive oil spiked with aniline-denatured rapeseed oil, that affected more than 20,000 people (World Health Organization, 1992).
Detection of olive oil adulteration with most other vegetable oils is not very difficult due to the differences in the fatty acid, triacylglycerol, or sterol composition of these oils (Aparicio & Aparicio-Ruiz, 2000). However, the adulteration of olive oil with some oils such as hazelnut oil is hard to detect with conventional methods at levels below 20% (Bøwadt & Aparicio, 2003). This is due to the similar chemical composition of the major and some minor components found in hazelnut and olive oils (Benitez-Sanchez, Len-Camacho, & Aparicio, 2003).
Some detection process is time consuming, and sometimes we have to run more than one analytical method for detection of adulteration. Therefore, a new detection method which will provide simple, fast and inexpensive identification of such adulteration is required.
Virgin olive oil is highly valued because it is traditionally obtained from olives without the use of heat and is regarded as better tasting and nutritionally favorable. Adulteration of olive oil can occur by mislabeling of less expensive products or by adding fewer expensive oils to increase the volume and increase profits. Adulteration in olive oil accomplish in three ways including:
Adulteration with other vegetable oils.
Adulteration with refined olive oil.
Adulteration with olive- pomace oil.
Usually, the authentication of vegetable oils is conducted by quantification of chemical components present in edible oils. Because of the numerous components of vegetable oils, many analytical procedures have been employed to identify and quantify them (Aparicio & Aparicio-Ruiz, 2000). Following traditional divisions, authentication studies were focused on two groups of compounds, the saponifiable and unsaponifiable matter. The saponifiable matter includes triglycerides, partial glycerides, esters of fatty acids with saturated fatty alcohols of linear chain, terpenic alcohols and free non-esterified fatty acids. The unsaponifiable matter, which makes up around 2% of all oils, includes many chemical substances of very different structure, such as alcohols of triterpenic structure, hydrocarbons, phytosterols and flavonoids, sterols, pigments, terpenic dialcohols, tocopherols and volatile compounds (Chen, et al., 2011).
Olive oil adulteration with most vegetable oils can be detected by conventional methods. For example, fatty acid composition is useful for the detection of adulteration of olive oil with the following vegetable oils: soybean, walnut, canola, rapeseed, peanut and mustard, even at levels of adulteration below 5% (Christopouloua, Lazarakia, Komaitisb, & Kaselimisb, 2004). Î”ECN42 (calculated from the difference between the theoretical and experimental equivalent carbon number 42 in triacylglycerols) can also be used to detect olive oil adulteration with the following vegetable oils: sunflower, soybean, cotton, corn, walnut, sesame, safflower, canola and rapeseed at levels as low as 1% (Christopouloua, et al., 2004).
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Detection of adulteration with refined oil usually is accomplished by official methods including:
Absorbency in ultraviolet
Trans fatty acids
Mechanical extraction and lack of elevated heat in the extraction process of virgin olive oil are the causes of low trans fatty acids in virgin olive oil. The maximum trans fatty acids in edible virgin olive oils are maximum 0.05% for C18:1 T and 0.05 for sum of both C18:2 T and C18:3 T, therefore detection of adulteration by heated oils (refined oils) can be done by trans fatty acids(Christopouloua, et al., 2004).
The sterol composition especially amount of campesterol and presence of steroidal hydrocarbons (sterenes) which are produced by the action of activated bleaching earths on sterols during the refining process of vegetable oils, were proposed for detection of frauds in oils. Since the stigmastadienes does not occur in olive , therefore, For oils sold as no refined, a limit of 0.15 mg/kg of stigmasta-3,5-diene (STIG) was applied, adopted by the International Olive Oil Council (Bonveh, Torrent, & F. Coll, 2001; International Olive Oil Council, 2009; Ranalli, Costantini, Mattia, & Ferrante, 2000).while, the amount of campesterol should not be more than 4% of total sterols(International Olive Oil Council, 2009). However, using stigmastadienes as an indicator for olive oil adulteration is reliable only when their concentration lies between 0.01 and 4 mg/kg. Furthermore, the campesterol content in some olive oils exceeds the 4% set by the EC regulation (Salvador, Aranda, & Fregapane, 1998). These two facts limit the use of these two sterols in detecting the presence of refined vegetable oils in olive oil.
Among vegetable oils, hazelnut oil has been used to adulterate olive oil due to its similar composition of triacylglycerols, fatty acids and major sterols (Mannina, et al., 2009). It is estimated that in the European Union, 4 million Euros per year are lost because of this adulteration (Ozen & Mauer, 2002). It is difficult to detect olive oil adulteration with hazelnut oil at levels below 20% using conventional methods for detecting the adulteration with other vegetable oils(Bøwadt & Aparicio, 2003).
Olive pomace is one of the main by-products of oil fruit processing. It contains fragments of skin, pulp, pieces of kernels and some oil. The oil present in the olive pomace undergoes rapid deterioration due to the moisture content that speeds up triacylglycerol hydrolysis. Refined olive-pomace oil is obtained from olive pomace after an extraction with authorized solvents and a refining process, which includes neutralization, deodorization and decolorization (Guimet, Ferre, & Boque, 2005). Several techniques such as determination of Erythrodiol and uvaol, aliphatic alcohols and wax content can be used to detect olive-pomace oil in virgin olive oil. However, they may be time-consuming and require sample manipulation. To overcome these handicaps other techniques have been applied.
As a conclusion, because there is not a standard method for detection of adulteration hazelnut oil in olive oil, and Level of Detection with current methods is high. Some detection process such as determination of wax content or sterol composition are time consuming, and sometimes more than one analytical method have to be run such as âˆ†ECN4, in which fatty acid composition by GC and triacylglycerols composition by HPLC have to be determined, Therefore a new detection method which will provide simple, fast and inexpensive identification of such adulteration is required.
Objective (s) of the Research
To compare the standard methods that have been used in detection process with rapid or non- standard methods in same condition.
To optimize the screened method for detection of adulteration in virgin olive oil.
To validate the performance of optimized method for detection of adulteration in virgin olive oil.
Virgin olive oil
Virgin olive oil, refined olive oil and olive-pomace oil will be purchased from olive oil mill or from a certified company. Other vegetable oils will be purchased from a local market.
Olive oil adulteration
Virgin olive oil will be adulterated by refined olive oil, olive-pomace oil and other vegetable oils in different percents.
Detection of adulteration
Detection process will be carried out on each sample by standard methods and with rapid or non- standard methods depend on adulterant oil.
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The best method for each adulterant regarding to level of detection will be selected.
For decreasing the level of detection the screened method will be changed.
The developed method shall be validated with spiked samples and after that by market samples.