**4. Quality control of olive oil**

Olive oil is subject to enormous analytical and sensory controls to assess its overall quality. These analyses evaluate the freshness of the oil regarding hydrolytic and oxidative alterations to ensure the conformity of products to their labels. For example, extra VOO by simple routine analyses (free fatty acids, peroxide value, specific extinction (E270 along with E232) and/or purity blending with other oils and *Olive Oil: Extraction Technology, Chemical Composition, and Enrichment Using Natural… DOI: http://dx.doi.org/10.5772/intechopen.102701*

contaminants. These criteria require detailed analyses (triglycerides contents, fatty acids, sterols, tocopherols, etc. …). Organoleptic characteristics (taste, odor, color, etc. …) also have to be taken into account.

As for other vegetable oils, the olive oil oxidation leads to natural phenomena alteration [46, 47]. This can be controlled since fruit harvest until oil storage. Because of oxidation, physicochemical parameters such as acidity, peroxide value and extinction specific at wavelength 270 (λ270 or λ270) have been selected as the backbone of olive oil quality determination by the International Olive Council [12]. Also, acidity of olive oil is classified into four grades: extra-virgin (Acidity < 0.8 g/100 g), fine-virgin (0.8 < Acidity < 2 g/100 g), ordinary virgin (2 < acidity < 3.3 g/100 g), and lampante olive oil (Acidity > 3.3) (**Table 2**) [12].

The variability of the extra VOO, acid value according to various parameters has been studied [47]. Oil oxidative state is examined from peroxide value and specific extinction coefficients (K232 or K270). These indicate the presence of primary and secondary oxidation products [1, 48]. The peroxide value of extra VOO oil must be below 20 mEq O2/kg and specific extinction K232 < 2.5. The other two main indices used to evaluate the secondary oxidation products are the following: p-anisidine value and specific extinction K270 [1, 49]. The International Olive Council (IOC) has set 0.22 and 0.25 as a limit value for both the extra VOO and VOO, respectively [12].

Furthermore, along with oxidation and acidity concerns, the quantification of major compounds such as fatty acids (**Figure 3**), and minor compounds, like sterols (**Figure 4**), polyphenols, tocopherols, minerals elements, and other bioactive molecules, are also of great importance for the purity and for detection of olive oil adulteration, which is a complex problem. Owing to its high cost and demand, fraudsters blend VOO with cheaper edible oils (most often with sunflower and soybean oils) and sometimes with low-quality olive oil. Today, the problem exceeds the borders of the main producer countries and it tackles the international level market. In addition to known risks of commercializing a mixture of vegetable oils. There is another type of adulteration resulting from the mixing of relatively low and high-quality olive oil, and the outcome is a product, which is sold as "high quality extra VOO". The control of adulteration, and authentication is of a crucial importance for the olive oil quality control. Codex Alimentarius (fats and oils), International Olive Council, and European Union Commission are dealing with the monitoring along with the regulation of VOO [50]. These international organizations have described the official control methods and have specified olive oil quality limits. Generally, all analytical techniques (chromatography, spectrophotometry, voltametric, differential scanning calorimetry), as well as several analytical methods, have been used to detect the adulteration of olive oil. Gas


#### **Table 2.**

*Limits established for acidity, peroxide index and extinction specific (K232 and K270) for each olive oil category.*

chromatography (GC), which analyzes oil fatty acids profile, can be used to detect virgin oil purity by distinguishing it from other vegetable oils such as sunflower, soybean, walnut, rapeseed, and canola oils [51]. Moreover, HPLC-technique can be used, to calculate, the difference between the theoretical and experimental equivalent carbon number (ΔECN42th). Likewise, the determination of phytosterols composition (namely campesterol Δ7-stigmasterol) using gas chromatography can be used to detect olive oil adulteration with low levels of cotton, corn, sunflower, soybean, and rapeseed oils [51]. In addition, Vietina et al. reported that the polymerase chain reaction (PCR) technique was demonstrated to be an efficient technique to detect VOO adulteration with cheaper vegetable oils by comparing their DNA melting profiles [52]. MS has also been used to detect the fraudulent presence of vegetable oils. Also, a lot of different techniques involving MS have been significantly developed, such as LC–MS, GC–MS, and MALDI-TOF/MS, which are of highly accurate identification [51]. Indeed, many other studies have also outlined the application of fluorescence spectroscopy, UV–Vis spectroscopy, [50] Fourier transform infrared spectroscopy [53] mid-infrared (MID) or near-infrared spectroscopy (NIR) [54] and Raman spectroscopy [55] for authentication and detection of adulteration of vegetables oil present in VOO [50]. Otherwise, differential scanning calorimetry (DSC) has also been used to detect argan oil purity by discriminating it from sunflower, high oleic sunflower as well as refined hazelnut oil [50]. Apetrei and Apetrei have investigated the use of the voltametric method based on modified EO


#### **Table 3.**

*Organoleptic attributes of olive oil.*

*Olive Oil: Extraction Technology, Chemical Composition, and Enrichment Using Natural… DOI: http://dx.doi.org/10.5772/intechopen.102701*

carbon paste-based sensors to determine the adulteration of VOO with soybean and sunflower oils [56].

On the other hand, identification of contaminants is one of the multiple checks that must be performed on oils. Vegetable oils have limited values for aromatic hydrocarbons polycyclics (PAHs), heavy metals, mycotoxins, phthalates, and pesticides. Although, the physicochemical characterization of olive oil is an essential step, it is not sufficient and organoleptic characteristics along with the above-mentioned supplementary analyses are required for a full picture of olive oil quality [1].

To satisfy consumers, organoleptic characteristics (color, taste, smell, etc.) must be taken into account. This is particularly important for olive oil. The organoleptic analysis is an essential step for successful food marketing. It is an integral part of evaluating olive oil. IOC has established a procedure to evaluate the organoleptic characteristics of VOO according to COI/T.20/Doc. [12] No 15/Rev. 102,018. It has classified such characteristics into positive and negative attributes as highlighted in **Tables 2** and **3**.

## **5. Olive oil enrichment with natural additives**

Oxidation of lipids including oils is a major concern to food industries [57, 58]. While, vegetable oils are endowed with a wide variety of endogenous antioxidants (pigments, vitamins, tocols, phenols, etc.), the use of exogenous antioxidants is widely practiced to enhance oxidative stability. In this regard, synthetic antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary butylhydroquinone (TBHQ ), as well propyl gallate are commercially used to extend oils' shelf life by delaying or even hindering lipids degradation. These molecules are considered as Generally Recognized as Safe (GRAS) preservatives with a concentration limit of 0.02% in oils and fats [59]. In contrast, some reports associated these molecules with health risks because of carcinogenesis, leading to a restriction of the use of the GRAS list and a reduction of their utilization in different countries [59]. For this reason, natural antioxidants are a good alternative to replace the synthetic ones in preserving vegetable oils including olive oil [59–61]. An overview of factors involved in the balance of antioxidants and pro-oxidants as well as synthetic and natural antioxidants are summarized in **Figure 7**.

Natural extracts sourced from various plant parts (peel, fruit, leaf, flower, and root) from different aromatic and medicinal herbs, agri-food residues and by-products were investigated for their antioxidant power as well as their use for the enrichment of olive oil with an emphasis on improving oxidative stability. Such natural extracts were proved to have a wide range of bioactive compounds were identified. These are mainly carotenoids and phenols [62, 63]. Promising results were obtained regarding the improvement of oxidative stability and shelf life of olive oil. Regarding the antioxidant activity of synthetic and natural additives, several mechanisms are involved. They act as free radical scavengers, inactivators of peroxides as well as other reactive oxygen species (ROS), singlet oxygen quenchers, metal ion chelators, quenchers of secondary oxidation products, and inhibitors of pro-oxidative enzymes, among other compounds [64]. Following these authors, antioxidants can be classified, based on their mode of action, into primary antioxidants. These break the oxidation chain reaction through scavenging free radical intermediates, however secondary antioxidants delay or even prevent oxidation through suppression of oxidation initiator, accelerators or regeneration of primary antioxidants.

**Figure 7.**

*An overview of factors involved in olive oil oxidative stability as well as natural and synthetic antioxidants. BHA, butylated hydroxyanisole; BHT, butylated hydrolxytoluene; TBHQ, tertiary butylhydroquinone; MUFA, monounsaturated fatty acids, and PUFA, polyunsaturated fatty acids.*
