Cultivar discrimination and prediction of mixtures of Tunisian extra virgin olive oils by FTIR

Application of the FTIR technique as a non-invasive tool to discriminate Portuguese olive oils with Protected Designation of Origin

Three Portuguese olive oils with PDO ('Azeite do Alentejo Interior', 'Azeites da Beira Interior' and 'Azeite de Trás-os-Montes') were studied considering their physicochemical quality, antioxidant capacity, oxidative stability, total phenols content, gustatory sensory sensations and Fourier transform infrared (FTIR) spectra. All oils fulfilled the legal thresholds of EVOOs and the PDO's specifications. Olive oils from 'Azeite da Beira Interior' and 'Azeite de Trás-os-Montes' showed greater total phenols contents and antioxidant capacities, while 'Azeites da Beira Interior' presented higher oxidative stabilities. Linear discriminant models were developed using FTIR spectra (transmittance and the 1st and 2nd derivatives), allowing the correct identification of the oils' PDO (100 % sensitivity and specificity, repeated K-fold-CV). This study also revealed that multiple linear regression models, based on FTIR transmittance data, could predict the sweet, bitter, and pungent intensities of the PDO oils (R2 ≥0.979±0.016; RMSE≤0.26±0.05, repeated K-fold-CV). This demonstrates the potential of using FTIR as a non-destructive technique for authenticating oils with PDO.

Discrimination of botanical origin of olive oil from selected Greek cultivars by SPME-GC-MS and ATR-FTIR spectroscopy combined with chemometrics

BACKGROUND

Consumers today wish to know the botanical origin of the olive oil they purchase. The objective of the present study was the development of robust chemometric models based on gas chromatography-mass spectrometry (GC-MS) and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) for the purpose of botanical differentiation of three commercial Greek olive oil cultivars.

RESULTS

Using the solid-phase microextraction technique (SPME), volatile compounds (VC) were obtained and analyzed by GC-MS. Five hydrocarbons and one ester were selected by the forward stepwise algorithm, which best discriminated the olive oil samples. From ATR-FTIR analysis, the spectral regions chosen from the forward stepwise algorithm were associated with CO stretching vibration of the esters of triglycerides and the CH bending vibrations of the CH₂ aliphatic group and double bonds. Application of the supervised methods of linear and quadratic discriminant cross-validation analysis, based on VC data, provided a correct classification score of 97.4% and 100.0%, respectively. Corresponding statistical analyses were used in the mid-infrared spectra, by which 96.1% of samples were discriminated correctly.

CONCLUSION

ATR-FTIR and SPME-GC-MS techniques in conjunction with the appropriate feature selection algorithm and classification methods proved to be powerful tools for the authentication of Greek olive oil. The proposed methodology could be used in an industrial setting for determination of the botanical origin of Greek olive oil. © 2020 Society of Chemical Industry.

Mid-Infrared Spectroscopy as a Valuable Tool to Tackle Food Analysis: A Literature Review on Coffee, Dairies, Honey, Olive Oil and Wine

Nowadays, food adulteration and authentication are topics of utmost importance for consumers, food producers, business operators and regulatory agencies. Therefore, there is an increasing search for rapid, robust and accurate analytical techniques to determine the authenticity and to detect adulteration and misrepresentation. Mid-infrared spectroscopy (MIR), often associated with chemometric techniques, offers a fast and accurate method to detect and predict food adulteration based on the fingerprint characteristics of the food matrix. In the first part of this review the basic concepts of infrared spectroscopy, sampling techniques, as well as an overview of chemometric tools are summarized. In the second part, recent applications of MIR spectroscopy to the analysis of foods such as coffee, dairy products, honey, olive oil and wine are discussed, covering a timespan from 2010 to mid-2020. The literature gathered in this article clearly reveals that the MIR spectroscopy associated with attenuated total reflection acquisition mode and different chemometric tools have been broadly applied to address quality, authenticity and adulteration issues. This technique has the advantages of being simple, fast and easy to use, non-destructive, environmentally friendly and, in the future, it can be applied in routine analyses and official food control.