A Systematic Chemometric Approach to Identify the Geographical Origin of Olive Oils

Abstract

The verification of the geographical origin of olive oils by analytical techniques is still a challenge. The goal of this work is to explore the application and accuracy of different chemometric tools combined with near infrared spectroscopy (NIR) based analytical methods in the field of geographical authenticity of olive oils. As olive oils associated with different geographical origins are mainly characterized by different fatty acid (FA) and triacylglycerol (TAG) compositions, NIR methods for the fast and reliable determination of these parameters are developed. Next, these NIR methods are used to characterize a comprehensive set of olive oils (n > 5000) derived from 19 different countries. This set of data is used to build a statistical workflow, which allows the determination of the geographical origin of unknown olive oil samples. First of all, the untreated data set is pretreated by k‐means clustering and the selection of the relevant analytical variables by principal component analysis (PCA) and linear discriminant analysis (LDA) and min/max normalization of all parameters. Subsequently, classification is performed with a reduced sample set of the 200 most similar samples identified by k‐nearest neighbor tool (kNN). For classification purpose kNN, LDA, naïve Bayes classifier, and logit regression are applied. Practical Applications: The established statistical workflow can be used to verify the geographical origin of olive oils. The application and usage of up to four different statistical models for classification purpose results in a superior probability of the predicted origin in comparison to the application of only one single statistical classification test. As standardized methods are used as reference methods for building the NIR methods, the FA and TAG composition and the iodine value can be either determined by the standard methods or by the described NIR method. The presented statistical approach will help to build up a system for the verification of the geographical origin of olive oils.

Development of Chemometric Models Based on a LC-qToF-MS Approach to Verify the Geographic Origin of Virgin Olive Oil

“…As a consequence, the National Reference Centre for Authentic Food (NRZ-Authent) in Germany was established in 2017 [ 2 , 3 ]. Moreover, the search for reliable and robust methods for the detection of food fraud is an ongoing story and many research groups dedicate a lot of time to this topic [ 5 , 6 , 7 , 8 , 9 ].…”

“…Recently, several papers on the differentiation of olive oil from different regions using different analytical methods combined with multivariate techniques have been published. Such methods are MS-based techniques [ 16 , 17 ], HPLC [ 18 ], genomics [ 19 ], stable isotope ratio analysis [ 5 , 20 ], NMR [ 9 , 21 , 22 ], NIR [ 7 ] or two-dimensional GC-MS [ 23 ]. Regarding the application of NMR in questions of origin verification there are only few studies available, mostly based on 1H-NMR as the generation of quantitative data is faster and simpler in comparison to 13C-NMR [ 21 ].…”

“…The presented model based on the developed extraction protocol allowed to differentiate olive oils from Italy, Greece and Spain with a correct classification of 96% during cross-validation [ 9 ]. Another analytical technique used for origin determination of olive oils is NIR [ 7 , 24 ]. The advantages of NIR spectroscopy are that no sample preparation is needed and the time for analysis per sample is short which makes it feasible to analyze a huge set of samples as needed for the development of reliable chemometric models.…”

“…Moreover, once the calibration for typical identity and quality parameters, like fatty acid and triacylglycerol composition, free fatty acids or peroxide value is established a multitude of parameters can be determined within one single analysis. As a result, the chemometric model build for origin verification can not only be based on the spectra but also on the classical parameters determined by NIR, as suggested by Gertz et al [ 7 ] who presented an approach based on the analysis of more than 5000 olive oil samples and different statistical approaches to identify the origin of olive oils by NIR.…”

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

“…Many methods have been developed to identify these changes. Targeted methods [ 1–4 ] 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.…”