Developing FT-NIR and PLS1 Methodology for Predicting Adulteration in Representative Varieties/Blends of Extra Virgin Olive Oils

It was previously demonstrated that Fourier transform near infrared (FT‐NIR) spectroscopy and partial least squares (PLS1) were successfully used to assess whether an olive oil was extra virgin, and if adulterated, with which type of vegetable oil and by how much using previously developed PLS1 calibration models. This last prediction required an initial set of four PLS1 calibration models that were based on gravimetrically prepared mixtures of a specific variety of extra virgin olive oil (EVOO) spiked with adulterants. The current study was undertaken after obtaining a range of EVOO varieties grown in different countries. It was found that all the different types of EVOO varieties investigated belonged to four distinct groups, and each required the development of additional sets of specific PLS1 calibration models to ensure that they can be used to predict low concentrations of vegetable oils high in linoleic, oleic, or palmitic acid, and/or refined olive oil. These four distinct sets of PLS1 calibration models were required to cover the range of EVOO varieties with a linoleic acid content from 1.3 to 15.5 % of total fatty acids. An FT‐NIR library was established with 66 EVOO products obtained from California and Europe. The quality and/or purity of EVOO were assessed by determining the FT‐NIR Index, a measure of the volatile content of EVOO. The use of these PLS1 calibration models made it possible to predict the authenticity of EVOO and the identity and quantity of potential adulterant oils in minutes.     

Prediction of quality of intact olives by near infrared spectroscopy

In this work we investigated the intact olive fruit quality prediction parameters measured directly by visible and near infrared spectroscopy (Vis/NIRS); the usefulness of a portable spectrometer is also assessed. The analysed parameters of the olive fruits were moisture, dry matter, oil content, oil free acidity and fruit maturity index. It was also studied whether NIR prediction of dry matter on olives may be more useful than NIR moisture measurement. Likewise, the results from the NIR prediction of olive oil contents related to dry matter as well as to fresh weight, were compared. Models for oil content were developed using Soxhlet extraction from dried olive paste as the reference analysis. Results indicate a good prediction potential of the models for the olive quality parameters analysed, with RPD ratios from 2.51 to 3.18. The successful NIR predictions of these quality parameters are reported for the first time. Practical applications: The technique presented here can expedite the milling procedure by allowing early detection of the olive quality and a quick calculation of the economic returns to the producers becomes possible. Furthermore, since oil quality depends largely on the optimal harvesting date when the olives should be taken to the mill, techniques that enable the monitoring of the oil content in olive fruit at different stages of maturity, even while still on the tree, become a useful and practical tool. This technique could allow monitoring the quality attributes of large amounts of the olive fruit entering the mill without the need of laboratory analysis that can only be conducted on a small number of olive fruit samples.     

Novel,Rapid Identification,and Quantification of Adulterants in Extra Virgin Olive Oil Using Near‐Infrared Spectroscopy and Chemometrics

A new, rapid Fourier transform near infrared (FT‐NIR) spectroscopic procedure is described to screen for the authenticity of extra virgin olive oils (EVOO) and to determine the kind and amount of an adulterant in EVOO. To screen EVOO, a partial least squares (PLS1) calibration model was developed to estimate a newly created FT‐NIR index based mainly on the relative intensities of two unique carbonyl overtone absorptions in the FT‐NIR spectra of EVOO and other mixtures attributed to volatile (5280 cm^?1) and non‐volatile (5180 cm^?1) components. Spectra were also used to predict the fatty acid (FA) composition of EVOO or samples spiked with an adulterant using previously developed PLS1 calibration models. Some adulterated mixtures could be identified provided the FA profile was sufficiently different from those of EVOO. To identify the type and determine the quantity of an adulterant, gravimetric mixtures were prepared by spiking EVOO with different concentrations of each adulterant. Based on FT‐NIR spectra, four PLS1 calibration models were developed for four specific groups of adulterants, each with a characteristic FA composition. Using these different PLS1 calibration models for prediction, plots of predicted vs. gravimetric concentrations of an adulterant in EVOO yielded linear regression functions with four unique sets of slopes, one for each group of adulterants. Four corresponding slope rules were defined that allowed for the determination of the nature and concentration of an adulterant in EVOO products by applying these four calibration models. The standard addition technique was used for confirmation.     

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.     

Natural antioxidants and volatile compounds of virgin olive oils obtained by two or three‐phases centrifugal decanters

Research has been carried out to ascertain the influence of different centrifugal decanters employed in olive process on oil yields and qualitative characteristics and composition of volatile compounds of virgin olive oil. Tests were performed in an olive oil mill equipped with centrifugal decanters at two or three‐phases. Results show that oil yields were similar and oils extracted from good‐quality olives do not differ in free fatty acids, peroxide value, UV absorptions and organoleptic assessment. Total phenols and o‐diphenols content as well as induction time values are higher in oils obtained by the centrifugal decanter at two‐phases, because it requires less quantity of water added to olive paste in comparison to the three‐phases centrifugal decanter. The amount of water added determines the dilution of the aqueous phase and lowers the concentration of the phenolic substances more soluble in vegetable waste water. Due to the partition equilibrium law the concentration of the same substances consequently diminishes in the oil. In this research, the coefficient of the partition equilibrium of total phenols between oil and vegetable water has been calculated and discussed. No significant difference occurred, due to the different decanters employed, in the average values of the volatile components of the head‐space of oils.     

Effects of the cold percolation system on the quality of virgin olive oil

The effects of the cold percolation system on the quality of virgin olive oil from two different Italian cultivars (Coratina and Oliarola) were determined. The quality was also compared with that of oil extracted with the current centrifugation system using a two‐phases decanter. Tests were performed in an industrial oil mill equipped with the two extraction systems. The oils extracted with cold percolation system showed, in all cases, lower free acidity, peroxide value, and ultraviolet (UV) absorption (K₂₃₂ and K₂₇₀) and higher polyphenol contents in comparison to oils obtained by two‐phases centrifugation. These results were confirmed by the autoxidation stability of the oils examined.     

Influence of olive crushing methods on the yields and oil characteristics

In the last years, metallic crushers substituted granite stone mill with some variations in the organoleptic oil characteristics. To control the influence of the crushing method on the yield and oil quality, the olive pastes were obtained using three different ways: (i) new metallic crusher at mobile knives; (ii) granite stone mill; (iii) double olive crushing by the metallic crusher and the granite stone mill. With the aim to ascertain the useful use of a new metallic crusher (at mobile knives), experimental tests were carried out in an industrial oil mill. This oil mill is equipped by a centrifugal decanter generating two oil flows: first and second extraction (recovery) oils. The results showed that the yields obtained by different methods were satisfactory. No statistically significant differences have been observed in terms of oil yield and quality when different crushing devices were used. All first extracted oils are extra virgin with similar organoleptic characteristics, especially for the fruity intensity and for the bitter and pungent taste, as confirmed by the composition of volatile substances and the content of phenolic oil compounds. The recovery oils (second extraction oils) showed, in contrast to first extraction oils, a more intense green colour and a higher content of total phenols. Practical applications: Processing of sound olives with the right ripening grade and good quality allows to easily obtain an extra virgin olive oil, with commercial qualitative parameters according to the European Union requirements. However, different olive crushing systems affect the concentrations of some compounds responsible of aroma and taste (phenolic compounds). The use of the more violent metallic crushers facilitates obtaining oils with total phenol content higher than when using a stone mill. Here we used a particular metallic crusher (at knives) that, however, is suitable to replace the granite stone mill when a less pungent and bitter oil is required.     

Comparison of fatty acid profiles and mid‐infrared spectral data for classification of olive oils

The composition of olive oils may vary depending on environmental and technological factors. Fatty acid profiles and Fourier‐transform infrared (FT‐IR) spectroscopy data in combination with chemometric methods were used to classify extra‐virgin olive oils according to geographical origin and harvest year. Oils were obtained from 30 different areas of northern and southern parts of the Aegean Region of Turkey for two consecutive harvest years. Fatty acid composition data analyzed with principal component analysis was more successful in distinguishing northern olive oil samples from southern samples compared to spectral data. Both methods have the ability to differentiate olive oil samples with respect to harvest year. Partial least squares (PLS) analysis was also applied to detect a correlation between fatty acid profile and spectral data. Correlation coefficients (R²) of a calibration set for stearic, oleic, linoleic, arachidic and linolenic acids were determined as 0.83, 0.97, 0.97, 0.83 and 0.69, respectively. Fatty acid profiles were very effective in classification of oils with respect to geographic origin and harvest year. On the other hand, FT‐IR spectra in combination with PLS could be a useful and rapid tool for the determination of some of the fatty acids of olive oils.     

On the importance of total polar phenols to monitor the stability of Greek virgin olive oil

A large number of virgin olive oil samples obtained from different areas in Greece were analyzed for various quality parameters. The work focuses on the colorimetric determination of total phenols with the Folin‐Ciocalteu reagent and its importance in predicting shelf life of virgin olive oil. The results indicate a good correlation of total polar phenol content with the stability of the oil. Colorimetric determination of ortho‐diphenol content does not seem to be a better means for predicting virgin olive oil stability. RP‐HPLC quantification of hydroxytyrosol and tyrosol in their free form gives poor results in the case of freshly extracted oils. It is concluded that until an easy‐to‐manage HPLC method will be available, which will quantify accurately both free and bound forms of hydroxytyrosol and other phenolics, the colorimetric method for the determination of total polar phenols remains a good practical means to evaluate the stability of virgin olive oil.     

Detection of Soft‐Deodorized Olive Oil and Refined Vegetable Oils in Virgin Olive Oil Using Near Infrared Spectroscopy and Traditional Analytical Parameters

The European Parliament identifies virgin olive oil (VOO) as one of the foods which are often subject to fraudulent activities. Possibilities of adulteration are the application of illegal soft deodorization of extra virgin olive oil (EVOO) or the commercialization of blends of EVOO with soft‐deodorized EVOO or refined vegetable oils. Despite the search for possibilities to prove the illegal soft deodorization of EVOO or the addition of cheaper vegetable oils to EVOO, suitable methods are still missing. Therefore, the aim of the study is to develop a new analytical and statistical approach addressing detection of mild deodorization or addition of refined foreign oils. For this purpose, VOOs are treated in lab‐scale for 1 h up to 28 days at different temperatures (20, 50, 60, 80,100, 110, and 170 °C) in order to simulate and study the effect of heat treatment on known analytical parameters by near infrared spectroscopy (NIR). A logit regression model enabling the calculation of the probability for a heat treatment is developed. This new methodology allows detecting both soft deodorized olive oils and blends of EVOO with cheaper full refined vegetable oils. Adding only 10% of full refined oil could be detected in extra VOO. Practical Applications: NIR methods combined with chemometrics have become one of the most attractive analytical tools to control quality of food. It is a simple, precise, and rapid method. All relevant analytical parameters of oxidative and thermal fat degradation can be determined in a single run and be used to detect adulterated virgin olive oils (VOOs). The use of a simple equation developed from the logistic regression using peroxide value, K‐values, p‐anisidine value, pyropheophytine, 1,2‐diacylglycerols, total polar compounds and monomeric oxidized triacylglycerols, and other well‐known parameters allows to detect mild deodorized olive oils or also blends of VOO with soft‐deodorized ones or the addition of low amounts of foreign vegetable oils. This technique has potential to be used as a screening method for the detection of adulterated olive oils using both the traditional laboratory methods and the corresponding NIR‐methods.     

Determination of the SiH content of hydrogen silicone oil by a combination of the fourier transform near infrared,attenuated total reflectance–fourier transform infrared,and partial least squares regression models

To verify the feasibility of the determination of the Si?H content (HC) of hydrogen silicone oil (HS‐oil) with Fourier transform near infrared (FT‐NIR) spectroscopy and attenuated total reflectance (ATR)–Fourier transform infrared (FTIR) spectroscopy combined with the partial least squares regression (PLS‐R) model, HS‐oil samples were synthesized from concentrated hydrosilicone oil (HC = 1.4 wt %), octamethylcyclotetrasiloxane, and hexamethyldisiloxane or prepared by the dilution of concentrated hydrosilicone oil with octamethylcyclotetrasiloxane. The FT‐NIR PLS‐R model (8695–4000 cm^?1, two principal components) was developed from the FT‐NIR spectral data, and the coefficient of determination for cross‐validation (R²) and the coefficient of determination for external validation (r²) were 0.992 and 0.995, respectively. The ATR–FTIR PLS‐R model (2302–2040 cm^?1, one principal component) was developed from the ATR–FTIR spectral data; it produced an R² of 0.995 and an r² of 0.996. This study demonstrated that the combination of FT‐NIR and ATR–FTIR spectroscopy with the PLS‐R model were successfully used to determine the HC of the HS‐oil. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40694.     

Effect of storage on the original pigment profile of spanish virgin olive oil

The present study was carried out on 12 virgin olive oils to determine whether one year's storage under mild conditions of 15°C and darkness affected the initial pigment composition of recently extracted virgin olive oil. Although the total pigment content remained constant, the individual contribution of each pigment changed. The acid compounds liberated from the fruits during the oil extraction process promote the beginning of chlorophyll pheophytinization and the isomerization of the 5,6-epoxide groups of the minor xanthophylls. During the first 3 mon of storage, there was a generalized increase in pheophytinization that was different for each oil (P<0.01, Duncan test) but was not correlated with the free acidity measured in them. At the same time, isomerized xanthophylls and allomerized pheophytins increased slightly. Following this stage, pyropheophytin a (a pigment not present in the initial oils), was detected; its concentration increased during storage. There were no significant differences in the final percentages of pyropheophytin a among the 12 oils, and the concentration of this new compound represented around 3% of the chlorophyll fraction. The pheophytin a/pyropheophytin a ratio always exceeded 20. All these small pigment transformations were signs that the oil had been stored. The content and class of pigments present in virgin olive oil are authentic indicators of its history prior to marketing.     

Enhancement of Bioactive Phenols and Quality Values of Olive Oil by Recycling Olive Mill Waste Water

Mature ‘Chondrolia Chalkidikis’ olives were processed in an industrial olive oil mill equipped with a three‐phase decanter. Water was added to the decanter at a 1:2 water‐to‐paste ratio. Olive mill waste water (ΟΜWW) was used to replace the added water at a rate of 50 or 100%. Following the final separation, the obtained oil was used for chemical analysis and sensory evaluation. All oils had similar acidity, peroxide and Κ values. OMWW‐treated olive oils presented higher total phenolic content and higher antioxidant activity based on DPPH and oven tests, but lower chlorophyll and carotenoids content. However, there was no significant difference between the 50 and 100% replacement. The phenolic profile of the treated olive oils analyzed by quantitative ¹Η NMR revealed more than twofold oleocanthal and oleacein as well as oleuropein and ligstroside aglycone contents than in the control. Sensory evaluation of treated oils also showed an enhancement of fruity, bitter and pungent attributes compared to the control.     

Influence of a new crushing technique on the composition of the volatile compounds and related sensory quality of virgin olive oil

The influence of a new crusher i.e. blade crusher on the quality of virgin olive oil from two different italian cultivars (Coratina and Oliarola) was determined. In addition the quality of this oil was compared with that of olive oil extracted with the traditional hammer crusher. Tests were performed in an industrial oil mill using the two different crushing instruments. Results obtained showed that quality parameters i.e. free fatty acids, peroxide value, UV absorption and total phenols content as well as the phenolic composition of oils were not significantly affected by the two different crushers used. On the contrary, the use of the blade crusher influenced the composition of the volatile compounds. In particular, the oils obtained using the blade crusher showed significant increases of some aldehydes such as 1‐hexanal and trans‐2‐hexenal, esters such as hexyl acetate and 3‐hexenyl acetate and a reduction of alcohols such as 1‐hexanol. Moreover, the identified pigments of the oils produced using the blade crusher were found at concentrations slightly lower than those in oils obtained after using the hammer crusher. Finally, results of the sensory analysis showed an improved organoleptic quality for the oils obtained using the blade crusher due to an increase of the cut‐grass and floral sensory notes.     

Automated ultrasound‐assisted method for the determination of the oxidative stability of virgin olive oil

A fast and automated method is proposed for determining the oxidative stability of virgin olive oil by using ultrasound. The ultrasound microprobe (3 mm in diameter) was directly immersed into the olive oil sample contained in a test tube. The most influential variables in the oxidation process, namely pulse amplitude, duty cycle, irradiation time, and sample amount, were optimized. The oil absorbance at 270 nm was continuously monitored by oil recirculation through a 0.1‐mm path length flow cell connected to a fiber optic microspectrometer. This short path length allowed the direct monitoring of absorbance without needing any sample dilution. The ultrasound energy was applied during 35 min, and the resulting increase in absorbance was continuously monitored. The difference between the final and the initial absorbance at 270 nm of a set of virgin olive oil samples was closely correlated with their oxidative stability calculated by the Rancimat method (R² = 0.9915). The resulting equation enabled the prediction of the oxidative stability of virgin olive oil in a short period of time (35 min), by using a simple, inexpensive, automatic and easy‐to‐use system.     

Determination of the Si?H content of hydrogen silicone oil by a combination of the fourier transform near infrared,attenuated total reflectance–fourier transform infrared,and partial least squares regression models

To verify the feasibility of the determination of the Si? H content (HC) of hydrogen silicone oil (HS‐oil) with Fourier transform near infrared (FT‐NIR) spectroscopy and attenuated total reflectance (ATR)–Fourier transform infrared (FTIR) spectroscopy combined with the partial least squares regression (PLS‐R) model, HS‐oil samples were synthesized from concentrated hydrosilicone oil (HC = 1.4 wt %), octamethylcyclotetrasiloxane, and hexamethyldisiloxane or prepared by the dilution of concentrated hydrosilicone oil with octamethylcyclotetrasiloxane. The FT‐NIR PLS‐R model (8695–4000 cm^?1, two principal components) was developed from the FT‐NIR spectral data, and the coefficient of determination for cross‐validation (R²) and the coefficient of determination for external validation (r²) were 0.992 and 0.995, respectively. The ATR–FTIR PLS‐R model (2302–2040 cm^?1, one principal component) was developed from the ATR–FTIR spectral data; it produced an R² of 0.995 and an r² of 0.996. This study demonstrated that the combination of FT‐NIR and ATR–FTIR spectroscopy with the PLS‐R model were successfully used to determine the HC of the HS‐oil. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40694.     

Effect of olive fruit freezing on oxidative stability of virgin olive oil

Several studies have suggested that the phenolic fraction plays an important role during storage and therefore in the shelf life of virgin olive oil. This investigation examines the effect of freezing olives (–18 °C) before processing into oil on the transfer of the phenolic compounds into the subsequent oil, and the consequential changes in oxidative stability. Oil samples obtained from frozen olives (24 h at –18 °C), crushed with and without preliminary thawing, were compared to a control sample; both oils were obtained using a two‐phase low‐scale mill. The oxidative stability in different samples was assessed in terms of primary and secondary oxidation products as measured by peroxide values and oxidative stability index times, respectively. The quality of the oil samples was also checked through the percentage of free acidity and the phenolic content. Phenols were determined by both spectrophotometric assays (total phenols and o‐diphenols) and HPLC‐DAD/MSD. The antiradical capacity of the phenolic fraction was determined by DPPH and ABTS spectrophotometric tests. These analyses showed that thawing of olives before oil extraction led to a significant loss of oxidative stability and phenols; in contrast, samples obtained from frozen olives that were not thawed before crushing showed qualitative characteristics similar to control samples.     

Characterization of virgin olive oil from Southern Tunisia

Fruits from three Tunisian cultivars of Olea europea L. grown in the southeast of Tunisia were harvested at the maturity stage of ripeness and immediately processed with a laboratory mill. There are as yet no data on the chemical composition of virgin olive oils from the southeast of Tunisia, an area characterized by an arid condition of growth for olive trees. Our results showed significant differences in the analytical parameters examined for the three cultivars such as fatty acid composition, total phenols and o‐diphenols, and the content of chlorophylls and carotenoids, confirming the importance of genetic factors in the chemical characteristics of the oil. Headspace solid‐phase microextraction (HS‐SPME) was applied to the analysis of volatile compounds of virgin olive oils. Forty‐eight compounds were isolated and characterized by GC‐RI and GC‐MS, representing 94.1–98.1% of the total amount. (E)‐Hex‐2‐enal, the main compound extracted by SPME, characterized the olive oil headspace for all samples. So, it was clearly shown that there were qualitative and quantitative differences in the proportion of volatile constituents from oils of the various cultivars.     

Chemical Composition of Turkish Olive Oil––Ayvalik

Although large amounts of olive oil are produced in Turkey, not much information on its chemical composition is available in the literature to date. The aim of this study was to evaluate the chemical composition of commercial olive oils produced from the Ayvalik olive cultivar in Canakkale, Turkey. Five different samples corresponding to the olive oil categories of extra virgin (conventional, extra virgin olive oil (EVOO), and organic extra virgin olive oil (OGOO) production), virgin olive oil (OO-1), ordinary virgin olive oil (OO-2) and refined olive oil (RFOO) were evaluated. Olive oils were collected from two consecutive production years. According to the free fatty acids, the absorbance values (K₂₃₂ and K₂₇₀), and peroxide values of all the samples conformed to the European standards for olive oil. The level of oleic acid was in the range of 68–73%; while the linoleic acid content was significantly lower in the refined olive oils. The tocopherol and polyphenol content was in the lower range of some European olive oils. However, pinoresinol was a major phenolic compound (5–77 mg/kg depending on the oil category). Its content was markedly higher than in many other oils, which would be a useful finding for olive oil authentication purposes.