Argan oil is a plant oil harvested from the seeds in the fruit of argan tree (Argania Spinosa ) a species native to Morroco. The argan tree belongs to Sapotaceae family which contains eight varieties namely Syderoxylon, Tsebona, Bumelia, Argania, Chrysophyllum, Pouteria, Calocapum and Pycnandra. The genus Argania consists of only one endemic species: Argania spinosa (syn. Argania syderoxylon L, Sideroxylon spinosum L Elaerandron argan Retz) (Khallouki et al,. 2005). It is protected by UNESCO 2007 and is extremely well adapted to drought and other harsh environmental typical conditions of southwestern Morocco (Gonzalvez et al,. 2009). The oil serves as a palatable or as a cosmetic agent. Edible argan oil is obtained from slightly roasted kernels, while the cosmetic grade oil is obtained from the unroasted kernels. Generally this oil composed of unsaturated fatty acid composition, particularly oleic and linoleic acids and rich in antioxidants compounds such as tocopherols which is just twice the amount to that present in olive oil. It consists of the presence of unique plant sterols such as spinasterol and schottenol and there are no other vegetable oils with a comparable phytosterol composition have been reported(Charrouf et al,. 1999). The Argan oil is a relatively new international product that nowadays is exported only by Morocco, although different companies in Europe and North America distribute it around the globe. The unique properties of the oil create a possibility that the export of such a product will increase in the near future (Cherki et.al., 2006). Also because of the low yield production and the time-consuming preparation method of the argan oil, which is responsible for its expensive nature (Oussama et al ., 2012). The average price of one bottle of argan oil in Europe is 100 euro per liter, which provides a good chance for the people to make it adulterated with some cheaper edible oil (olive oil, sunflower oil, soyabean oil and some other oils).Thus it is necessary to make the quality control of the oil by preventing the possible adulteration.
Adulteration usually refers to the process of addtion of certain foreign or harmful quality of substances in the food responsible for reducing the quality of substances and thus makes it unfit for consumption. The adulteration of high quality oil with cheap vegetable oils is a frequent problem from regulatory agencies, oil suppliers and consumers. The ability of the food industry and regulatory bodies to authenticate and control food constituents and check their origins is increasingly important (Gonzálvez et al., 2009). Many analytical techniques have been developed so far for adulteration detection in oils like as, by using HPLC (Hamdy et al., 2012), Gas chromatography (Hilali et al., 2007), Solid-Phase Microextraction Gas Chromatography with Flame Ionization Detection (SPME-GC-FID, Fluorescence (Poulli et.al., 2006) and the NMR spectroscopy (Fragaki et.al., 2005). Few studies has also been done in order for the revelation of argan oil adulteration using electronic nose and voltammetric electronic tongue (Bougrini et al., 2014), inductively coupled plasma optical emission spectrometry. But these studies are expensive, time-consuming and expensive in nature. Thus there is a need to develop a technique which will overcome all these drawbacks and useful for quality control and the food adulteration detection.
FT-IR spectroscopy provides a way for measuring the chemical bonds present in the molecule by the characteristic absorption of infrared radiation and its corresponding spectrum in the molecular vibrational spectrum. FT-IR spectroscopy offers both the qualitative and quantitative analysis of agricultural products and is used as an alternative to time-consuming, wet-chemical, and destructive techniques. As this technique is fast; a sample can be analyzed in a fraction of the minute, simultaneously collects all light frequencies that are transmitted or reflected back from the sample.Thus the technique has been used for the non-destructive estimation of the agricultural and food products.
A study has been done using FT-IR spectroscopy in conjugation with partial least squares regression analysis for the accurate determination of the percentage composition of the four essential oils (wintergreen, tea tree, rosemary, and lemon eucalyptus oils) adulterated with lemongrass essential oil or peppermint essential oil (Elzey et al., 2016). Further, FT-IR spectroscopy has been used to quantify adulteration of extra virgin olive oil with refined oils and different types of vegetable and nut oils (Kupper et al., 2001; Lai et al., 1995; Marigheto et al., 1998 and Tay et al., 2002). Also, the study has been done for the adulteration detection of avocado oil by the use of adulterants (sunflower, canola and canola oils) by the use of FT-IR spectroscopy in combination with Partial Least Squares (Islas et al., 2012).
PLSR analysis analysis method is a supervised classification method used for both classification and prediction. PLSR examines the essential contributing variables or features within the spectra and extracts the relevant information from the spectral data set. The first step is to develop a PLS regression model of the reference property values in a Y-variables set. The second step is to develop the PLS regression model to predict or classify new samples from the X-variables
This study focusses for checking the authenticity of argan oil blended with olive oil using FT-IR spectroscopy technique using PLS along with variable selection method. So the main objective of this study is to demonstrate the applicability of infrared spectroscopy as a rapid analytical method for the quantitative determination of argan oil adulteration with the olive oil in order to ensure the quality of oils.