Differentiation of mixtures of monovarietal olive oils by mid‐infrared spectroscopy and chemometrics

Fourier transform infrared (FT‐IR) spectroscopy in combination with chemometric techniques has become a useful tool for authenticity determination of extra‐virgin olive oils. Spectroscopic analysis of monovarietal extra‐virgin olive oils obtained from three different olive cultivars (Erkence, Ayvalik and Nizip) and mixtures (Erkence‐Nizip and Ayvalik‐Nizip) of monovarietal olive oils was performed with an FT‐IR spectrometer equipped with a ZnSe attenuated total reflection sample accessory and a deuterated tri‐glycine sulfate detector. Using spectral data, principal component analysis successfully classified each cultivar and differentiated the mixtures from pure monovarietal oils. Quantification of two different monovarietal oil mixtures (2–20%) is achieved using partial least square (PLS) regression models. Correlation coefficients (R²) of the proposed PLS regression models are 0.94 and 0.96 for the Erkence‐Nizip and Ayvalik‐Nizip mixtures, respectively. Cross‐validation was applied to check the goodness of fit for the PLS regression models, and R² of the cross‐validation was determined as 0.84 and 0.91, respectively, for the two mixtures.     

Near infrared spectral patterns of fatty acid analysis from fats and oils

A near infrared (NIR) spectral pattern of oil contains information about fatty acid composition, because NIR absorption bands around 1600–1800 nm and 2100–2200 nm are due to the straight carbon chain andcis double bonds, respectively. This study was undertaken to build a foundation for the rapid determination of the fatty acid composition in oil by an NIR method. First, NIR spectra of pure triglycerides were measured and characterized. Fatty acid compositions could be estimated roughly by comparing the spectra of fats and oils (butter fat, pig milk fat, soybean oil and palm oil) with those of pure triglycerides. Secondly, the NIR spectra of these fats and oils were reconstructed by summation of the triglyceride spectra, which are multiplied by factors corresponding to the fatty acid composition of the sample determined by gas chromatography. The calculated spectra agree with the originals, especially for that of soybean oil. However, in order to reconstruct spectra precisely, it may be necessary to reevaluate the loading weight of each triglyceride, which was equal in this study. Part of this study was presented at the 3rd International Conference on Near Infrared Spectroscopy on June 28, 1990, Brussels, Belgium.     

Piedmont olive oils: Compositional characterization and discrimination from oils from other regions

Piedmont olive oils collected in 2010 were characterized, for the first time, in terms of their fatty acid profile using GC and ¹H NMR and compared to other oils from five Italian regions. Applying NMR spectroscopy on the olive oil samples, without manipulation, it is possible to calculate the proportion of the different acyl groups in the oil samples. As the area of the signals is proportional to the number of each type of proton in the sample, saturated, monounsaturated (oleic acid) and polyunsaturated (linoleic and linolenic acids) fatty acids were determined. All analyzed samples can be categorized as virgin olive oil extra quality according to the oleic/linoleic ratio. Based on a preliminary geographical investigation, olive oils produced in the North of Italy show a good separation from those from Central and Southern regions. Practical applications : Oil characterization of new products is the basis for further nutritional and food technological investigations and the quality of edible oils is of great concern especially for products available on the market. The two adopted techniques show a remarkable agreement in the evaluation of fatty acid composition of oil samples. Also, this research, by means of ¹H NMR, provides information on geographical origin of the olive oils of Northern Italian regions with respect to Central and Southern regions.     

Phenolic profiles of Turkish olives and olive oils

Phenolic compound distribution of Turkish olive cultivars and their matching olive oils together with the influence of growing region were investigated. One hundred and one samples of olives from 18 cultivars were collected during two crop years from west, south and south‐east regions of Turkey. The olives were processed to oils and both olive and olive oil samples were evaluated for their phenolic compound distribution. The results have shown that main phenolics of Turkish olives were tyrosol, oleuropein, p‐coumaric acid, verbascoside, luteolin 7‐O‐glucoside, rutin, trans cinnamic acid, luteolin, apigenin, cyanidin 3‐O‐glucoside and cyanidin 3‐O‐rutinoside. Oleuropein and trans cinnamic acid were present in higher amounts among all phenolics. Principal component analyses showed that the growing region did not have drastic effect on phenolic profile of olives. The major phenolic compounds of olive oils were tyrosol, syringic acid, p‐coumaric acid, luteolin‐7‐O‐glucoside, trans cinnamic acid, luteolin and apigenin. Luteolin is a predominant phenolic compound in almost all oil samples. Total phenol concentrations of Southeast Anatolian oils were found to be lower than those of the other regions.     

Near‐infrared spectroscopy for analysis of oil content and fatty acid profile in almond flour

Almond kernels show large variability for oil content and fatty acid profile. The objective of this research was to evaluate the potential of near infrared (NIR) reflectance spectroscopy (NIRS) for the analysis of these traits in almond flour. Ground kernels of 181 accessions collected in 2009 were used for developing calibration equations for oil content and concentrations of individual fatty acids. Calibration equations were developed using second derivative transformation and modified partial least squares regression. They were validated with samples from 179 accessions collected in 2010. The accuracy of calibration equations was measured through the coefficient of determination (r²) in external validation and the ratio of the SD in the validation set to the standard error of prediction (RPD). Both r² and RPD were high for oil content (r² = 0.99; RPD = 9.24) and concentrations of oleic (r² = 0.97; RPD = 5.37) and linoleic acids (r² = 0.98; RPD = 7.35), revealing that calibration equations for these traits are highly accurate. Conversely, the accuracy of the calibration equations for palmitic (r² = 0.54; RPD = 1.41) and stearic acids (r² = 0.52; RPD = 1.44) was too low for allowing their application in practice. NIRS discrimination of oil content and concentrations of oleic and linoleic acids was mainly based on the spectral region from 2240 to 2380 nm. Practical applications : NIRS is a high‐throughput analytical technique that allows fast measurement of several traits in a single analysis without using chemical reagents. We evaluated the feasibility of analyzing oil content and concentrations of palmitic, stearic, oleic, and linoleic acids in almond flour using fruits collected during 2 years from a world germplasm collection. The fruits collected in 2009 were used for NIRS calibration, whereas the fruits collected in 2010 were used for validation. NIRS equations were highly accurate for measuring oil content and concentrations of oleic and linoleic acids, which are important traits defining the quality of almond flour for specific uses in the food industry. These results have applications both in the research laboratory and the food industry, where NIRS is becoming a widely used technique for quality control.     

Using lipid profiles and genotypes for the characterization of Corsican olive oils

In 2004, the Corsican producers of olive oils obtained a French protected designation of origin (PDO) “huile d'olive de Corse”, but up to now specifications of Corsican oil production do not clearly indicate the oil attributes related to the territory of production. That is why the fatty acid and triacylglycerol (TAG) compositions of olive oils from the nine main cultivars used to produce oils under PDO were determined and related to the olive variety. The results showed (i) that the nine cultivars covered only four olive varieties, as revealed by random‐amplified polymorphic DNA markers, (ii) that the lipid composition of oils is strongly dependent on the variety, and (iii) that the lipid composition of the four varieties is completely discriminated on the basis of the proportions of four TAG (OOO, OOL, PoOO, OOL) and one fatty acid (18:0). These results clearly establish the relationships between some characteristics of oils and the area of production (Corsica) for at least three varieties that are originated from Corsica. For the fourth variety, other investigations on minor compounds and on sensory attributes of oils must be undertaken to link some oil traits to the territory of production.     

Calculating the lodine value for marine oils from fatty acid profiles

The iodine values of marine oils were directly calculated from fatty acid profiles by using reacting ratios (calculation factors) between I₂ (iodine) and either the fatty acids bound to a triglyceride or the free fatty acids. A total of 20 factors were incorporated from C14:1 to C24:1, placed into an Excel® spreadsheet, and used to calculate the iodine values. The calculated values were then compared to the oil’s iodine value obtained by the traditional titration method. The results indicate that this method can be used to obtain the iodine value of marine oils directly from the oil’s fatty acid composition, thus giving two results from one analysis.     

Logit modeling for classification of monocultivar olive oils from southwest Spain: A preliminary study

A characterization study of the main olive oil cultivars of southwest Spain (Picual, Arbequina, and Verdial) has been performed in order to establish logistic regression models. Several quality characteristics (free acidity, peroxide value, K₂₃₂, K₂₇₀, oxidative stability index) and chemical data (fatty acids, sterols, erythrodiol–uvaol composition) were measured. Logit regressions were used to evaluate the correlation of the parameters and to create models that allow saving costs on identifying oils as Arbequina, Picual, or Verdial type. Multiple logit regression models were developed: one for Arbequina, three models for Picual, and two models for Verdial cultivar, allowing in this way to minimize the cost for classifying oil samples. Practical application: The olive oil marketing is increasingly focused on the chemical differentiation and characterization of the product because the chemical composition of these virgin oils is responsible for their valuable sensory and nutritional properties. Here we present a characterization study (quality characteristics and chemical data) from the main olive oil cultivars of southwest Spain, Picual, Arbequina, and Verdial, as a first step for the traceability of these three types of monocultivar virgin olive oils. The results may be used as a training to create models for other olive oil cultivars.     

Characterization and chemometric study of crude and refined oils from table olive by‐products

Table olive processing produces defective fruits and the conditioning operations give rise to solid by‐products which are processed to obtain oil. In this study, the most relevant characteristics of crude oils extracted from table olive by‐products were high average acidity values (4.5%, green olives; 8.1%, ripe olives), ECN42 values of 0.34 (green olives) and 0.10 (ripe olives), while 2‐mono‐palmitin averaged 0.92%. The overall content of sterols was 2257 mg/kg (green olives) and 1746 mg/kg (ripe olives), while the concentration of cholesterol was 36 mg/kg (green olives) and 19 mg/kg (ripe olives). The effect of refining was mainly reflected by a decrease in acidity and sterols. Although most characteristics were in agreement with the established regulation for olive oil, the overall trans fatty acid content, the low apparent β‐sitosterol content, and the relatively high cholesterol content prevented their inclusion into classes of crude or refined lampante or pomace olive oils, not even into the vegetable oil category. Therefore, the oils analyzed should be considered for non‐edible purposes. The physicochemical characteristics used for chemometric discrimination permitted discrimination among types of oils (crude, 100%; physically refined, 90%; chemically refined, 100%), elaboration styles (green and ripe olives, 100%) and cultivars (Gordal, Manzanilla, Hojiblanca and Cacereña, 100%), with the sterol composition being the most useful parameter for discrimination.     

Chemical and sensorial changes of Croatian monovarietal olive oils during ripening

The aim of this investigation was to determine the impact of fruit ripening on chemical and sensorial changes in monovarietal olive oils obtained from two important olive cultivars grown in Croatia, Bu?a and ?rna. In Bu?a oils peroxide value, K₂₃₂ and K₂₇₀ increased during ripening, while no differences among three ripening stages in ?rna oils were observed. Oils of both cultivars at the later ripening stages had higher free acidity level and lower sensory score followed by mild loss in almost all positive sensory characteristics. Total phenols and antioxidant capacity decreased in Bu?a oils during fruit ripening, while in ?rna oils reached maximum level in purple stage and then progressively decreased in the black ripening stage. Oleic acid level slightly increased during ripening in both cultivar oils. Linoleic acid decreased in Bu?a oils obtained from black fruits while palmitic acid decreased in ?rna oils during ripening. In both monovarietal oils chlorophyll and carotenoids concentrations decreased during ripening. The two cultivars had different course of total aldehydes, total esters and total ketones during ripening, while total alcohols were the highest in oils from purple ripening stage and then decreased as ripening progress. Practical applications: During the ripening, the chemical composition of olive fruit changes influencing the quality grade, oxidative stability, sensory characteristics and nutritional value of the obtained products. The cultivars characterized by a similar trend of ripening process could have different course of chemical and sensorial changes in oil during fruit ripening. Therefore, knowledge about these changes is important for determination of proper harvest time of single cultivar to achieve optimum of its potential regarding desirable characteristics of obtained oil.     

Application of principal-component analysis on near-infrared spectroscopic data of vegetable oils for their classification

In the near-infrared (NIR) spectra of oil, information about fatty acid composition is concentrated in the range of 1600–2200 nm. Principal-component analysis (PCA) was applied on the standardized full NIR spectral data of this region for vegetable oils to totally capture the NIR spectral pattern. Nine varieties of vegetable oils (soybean, corn, cottonseed, olive, rice bran, peanut, rapeseed, sesame and coconut oil) could be successfully classified from their PCA scores. Examining the contribution of wavelengths to PCA scores showed that wavelengths with a high loading weight were assigned to characteristic absorption regions that correspond to specific fatty acid moieties. This classification is related to the fatty acid composition of an oil, and it can be carried out rapidly and easily after eigenvectors were obtained.     

Characterisation of virgin olive oils from European olive cultivars introduced in Tunisia

The behaviour of three European olive varieties, Ascolana Tenera, Koroneiki and Picholine, cultivated in the north of Tunisia, was compared to an autochthonous variety, Chétoui. Most of the quality indices and the fatty acid composition showed significant variations between the olive oils. Among the introduced varieties, the Picholine cultivar had the highest value of oleic acid (61%) whereas the Ascolana Tenera cultivar was noteworthy for its lowest content of phenolic compounds (175 mg/kg) and presented the highest level of palmitic acid. The Chétoui variety presented a high content of oleic and linoleic acids. But all samples, both the autochthonous Chétoui and the introduced cultivars, have similar levels of antioxidant compounds, with the exception of phenols. The aroma composition showed significant differences between the oils from the foreign cultivars. The major volatile component was the C‐6 aldehyde fraction whose content varied greatly between the different varieties studied: The E‐2‐hexenal content ranged from 1.6 mg/kg of oil in the Ascolana Tenera variety to >5 mg/kg for the Picholine and Koroneiki cultivars, whereas the Chétoui variety had the lowest levels of volatile compounds, with the exception of the hexanal level which was tenfold higher than in the foreign cultivars. Therefore, our results showed that two of the introduced varieties, Koroneiki and Picholine, showed good adaptation to the Tunisian cultivation conditions. So far, we claim the possibility to develop the successful cultivation of these latter imported varieties in the country.     

Quality characteristics of olive leaf‐olive oil preparations

Olive leaf‐olive oil preparations were obtained by vigorous mixing at various levels of addition (5, 10, 15%w/w) of new or mature leaves. After removal of the plant material via centrifugation, quality and sensory characteristics of the preparations were determined. Oxidative stability (120°C, 20 L/h) and DPPH radical scavenging were increased ～2–7 fold depending on the level of leaves used due to enrichment with polar phenols, mainly oleuropein, and a‐tocopherol. The extraction process affected the chlorophyll content and organoleptic traits as indicated by acceptability and preference tests (n = 50). Forty‐four % of the panelists identified a strong pungency in preparations with 15% w/w new leaves. Fifty‐four % of them identified a bitter taste in those with 15% w/w mature leaves, which was attributed to high levels of oleuropein (～200 mg/kg oil). Olive leaf‐olive oil preparations had interesting properties regarding antioxidants present that can attract the interest of a functional product market. Practical applications: The wider use of olive oil and derived products is highly desirable. In this sense, the current study presents data that support introduction to the market of a new specialty olive oil based solely on olive tree products (olive oil and leaves). Thus, in addition to olive oil and olive paste, a new product, that is an olive oil enriched with olive leaf antioxidants, especially oleuropein produced via a “green” technique (mechanical means instead of extraction with organic solvent) can be made available for consumers.     

Calorimetry of edible oils: Isothermal freezing curve for assessing extra‐virgin olive oil storage history

The calorimetric method described here investigates the solid‐liquid phase transitions in a Tuscan extra‐virgin olive oil in order to evaluate the changes induced by light exposition. The parameters of the freezing and the melting curves show high sensitivity to oil quality degradation, in agreement with the data from routine tests at disposal. Possible applications of the method are discussed.     

Predicting temperature-dependence viscosity of vegetable oils from fatty acid composition

The viscosities of 12 vegetable oils were experimentally determined as a function of temperature (5 to 95°C) by means of a temperature-controlled rheometer. Viscosities of the oil samples decreased exponentially with temperature. Of the three models [modified Williams-Landel-Ferry (WLF), power law and Arrhenius] that were used to describe the effects of temperature on viscosity, the modified WLF model gave the best fit. The amounts of monounsaturated FA or polyunsaturated fatty acids (PUFA) highly correlated (R ²>0.82) with the viscosities of the oil samples whereas and the amounts of saturated or unsaturated FA. An exponential equation was therefore used to relate the viscosity of these vegetable oil samples to the amounts of monounsaturated FA or PUFA. The models developed are valuable for designing or evaluating systems and equipment that are involved in the storage, handling, and processing of vegetable oils.