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

Abstract

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. R 2 : coefficient of determination; d) RMSEP: root mean square error of prediction; e) MD: limit of Mahalanobis distances.

Near UV-Vis and NMR Spectroscopic Methods for Rapid Screening of Antioxidant Molecules in Extra-Virgin Olive Oil

“…Among the different spectroscopic techniques, infrared (IR) [ 15 , 16 ] and near infrared (near-IR) spectroscopies [ 17 ] have recently attracted much attention due to the very fast analyses and to the development of specific multivariate mathematical tools to rapidly detect typical olive oil adulterations [ 18 ]. These techniques are mostly centered on the identification and quantification of the fatty acid components and their derivatives [ 16 , 19 ].…”

Olive oil mixtures. Part two: Detection of soft deodorized oil in extra virgin olive oil through diacylglycerol determination. Relationship with free acidity

“…It is a fact that other authors have proposed interesting approaches through which lower percentages (20 %) of soft deodorized olive oils might be detected. Such is the case of Gerzt and colleagues (Gertz, Matthäus, and Willenberg, 2020) who developed a statistical model based on twelve analytical parameters to verify the authenticity of EVOO, including that mixed with soft deodorized oil. The results are different equations combining the analyzed parameters, which can be either determined by the Official Methods or by NIR.…”

“…We chose such approach following our trend of using well-known, widely established routine parameters, avoiding in this way more complicated strategies, e.g. chemometric methodologies, that although widely used in the field of olive oil authentication (Bosque-Sendra, Cuadros-Rodríguez, Ruiz-Samblás, and de la De la Mata, Domínguez-Vidal, Bosque-Sendra, Ruiz-Medina, Cuadros-Rodríguez, and Ayora-Cañada, 2012;Avramidou, Doullis, and Petrakis, 2018;Gertz, Matthäus and Willenberg, 2020), normally requires a more specific personnel training and laboratory equipment. Therefore, we hypothesize that, since there is a relationship between free acidity and DAG concentration (both of them come from triacylglyceride hydrolysis and/or biosynthesis), and that such relationship disappears once the oil has gone through a refining process (free fatty acids are removed during the deodorization step), it will be possible to detect the presence of soft deodorized oil in EVOO by using a mathematical combination of both measurements at least to a certain extent.…”

Clarifications of the Carbonyl and Water Absorptions in Fourier Transform Near Infrared Spectra from Extra Virgin Olive Oil

“…[12] The former permits the identification of samples based on the availability of reliable authentic samples, or by comparison to samples that have been accurately analyzed using traditional chemical methods. [4,6,10,11] The latter emphasizes the fact that each FT-NIR spectrum represents the overtone and combination absorptions of all components present in the sample in question. For most publications in which spectroscopic techniques were used, calibration models were developed based on sets of samples that had been extensively investigated using traditional chemical methods, but generally no attempt was made to make these models universal.…”

“…Many methods have been developed to identify these changes. Targeted methods [1][2][3][4] are generally limited because of great varietal differences in composition [5] and because specific mixtures can easily mimic the fatty acid (FA) composition of EVOO by clever manipulation. Therefore, to ensure the authenticity of EVOO, multiple targeted tests are generally conducted which are both costly and time-consuming.…”