A spectroscopic and chemometric study of virgin olive oils subjected to thermal stress

Application of vibrational spectroscopic techniques for determination of thermal degradation of frying oils and fats: a review

Deep fried foods are popular among consumers due to their unique taste and texture. During the process of deep-frying, oil is subjected to a high temperature that results into the generation of harmful compounds. The repeated usage of frying oil is a common exercise and associated with various health hazards. Thus, determination of frying oil quality is a critical practice to follow. The chemical methods employed to determine the quality of frying oil are destructive and require large amount of harmful chemical, thus researchers are exploring the application of various vibrational spectroscopic techniques for this purpose. The first part of this review provides a detailed insight into fundamental theoretical aspects of two main vibrational spectroscopic techniques (infrared and Raman spectroscopy) and chemical alteration in frying oils under thermal stress. While in the following parts, the application of near-infrared (NIR) and Fourier transform infrared (FTIR) and Raman spectroscopy for evaluating the quality of various frying oils and fats under thermal stress has been discussed. It is anticipated that this review paper can serve as a reference source for impending research in this field.

Getting inside on virgin olive oil (VOO) photooxidation kinetics through combined generalized 2D correlation analysis and moving window 2D correlation analysis of ATR-FTIR spectra

The generalized two-dimensional correlation spectroscopy (g2D-COR spectroscopy) analysis combined with its extended version moving-window 2D-COR (MW-2D-COR) was performed on a set of kinetic ATR-FTIR spectral data. The former is a mathematical method that is applied to a set of spectra collected for a sample exposed to an external perturbation (e.g. storage time). Virgin olive oils (VOOs) of similar fatty acid composition, chlorophyll, and a-tocopherol content were photooxidized (10,912 Lx, no headspace, 24 h). The proposed approach revealed hidden information under specific ATR-FTIR bands and the order of events was established using appropriate rules. MW-2D-COR analysis displayed the evolution of changes during storage. In this way, the detection of the time interval upon which spectral changes are observed was evidenced. As an overview, MW plots of the analyzed samples revealed three time-zones in which changes tend to maximize, with the first one to reach a peak at ~2.5 h. The area around 2850-2930 cm^-1 including bands assigned to the symmetric and asymmetric stretching vibration of the aliphatic -CH₂- bonds, was the one found to be affected in all VOOs. The time interval upon which spectral changes are first detected in the corresponding area could serve as an index for the commencement of the loss of freshness. Present findings highlight the need to combine the two types of correlation analyses to obtain meaningful information on VOO photooxidation kinetics. Lipid scientists may gain an extra tool in their efforts to understand oxidation phenomena.

Chemometric study of Andalusian extra virgin olive oils Raman spectra: Qualitative and quantitative information

Authentication of extra virgin olive oil (EVOO) is an important topic for olive oil industry. The fraudulent practices in this sector are a major problem affecting both producers and consumers. This study analyzes the capability of FT-Raman combined with chemometric treatments of prediction of the fatty acid contents (quantitative information), using gas chromatography as the reference technique, and classification of diverse EVOOs as a function of the harvest year, olive variety, geographical origin and Andalusian PDO (qualitative information). The optimal number of PLS components that summarizes the spectral information was introduced progressively. For the estimation of the fatty acid composition, the lowest error (both in fitting and prediction) corresponded to MUFA, followed by SAFA and PUFA though such errors were close to zero in all cases. As regards the qualitative variables, discriminant analysis allowed a correct classification of 94.3%, 84.0%, 89.0% and 86.6% of samples for harvest year, olive variety, geographical origin and PDO, respectively.

Chemometric applications to assess quality and critical parameters of virgin and extra-virgin olive oil. A review

Today virgin and extra-virgin olive oil (VOO and EVOO) are food with a large number of analytical tests planned to ensure its quality and genuineness. Almost all official methods demand high use of reagents and manpower. Because of that, analytical development in this area is continuously evolving. Therefore, this review focuses on analytical methods for EVOO/VOO which use fast and smart approaches based on chemometric techniques in order to reduce time of analysis, reagent consumption, high cost equipment and manpower. Experimental approaches of chemometrics coupled with fast analytical techniques such as UV-Vis spectroscopy, fluorescence, vibrational spectroscopies (NIR, MIR and Raman fluorescence), NMR spectroscopy, and other more complex techniques like chromatography, calorimetry and electrochemical techniques applied to EVOO/VOO production and analysis have been discussed throughout this work. The advantages and drawbacks of this association have also been highlighted. Chemometrics has been evidenced as a powerful tool for the oil industry. In fact, it has been shown how chemometrics can be implemented all along the different steps of EVOO/VOO production: raw material input control, monitoring during process and quality control of final product.

Rapid determination of olive oil oxidative stability and its major quality parameters using vis/NIR transmittance spectroscopy

This paper reports the determination of the olive oil stability index (OSI) by multivariate models from the visible and near-infrared spectrum. The technique proposed is rapid and nondestructive and can be used as a multiparametric method. Moreover, it does not require specific instrumentation, and it is environmentally friendly. The determination of the OSI using the Rancimat instrument was used as a reference method. Predictive visible and near-infrared (vis/NIRS) models were obtained from partial least squares (PLS) for the OSI, showing satisfactory performance in independent tests as proven by the R(2) values of 0.93 and 0.94 from the calibration and the residual predictive deviation (RPD) of the external validations of 3.30 and 3.00, respectively. Predictive models for the determination of free fatty acids, peroxide value, and conjugated dienes were also developed, and their satisfactory performances were demonstrated by RPDs of 3.14, 2.84, and 2.56; hence, its multiparametric determination together with OSI would be possible.

New filtration systems for extra-virgin olive oil: effect on antioxidant compounds, oxidative stability, and physicochemical and sensory properties

The purpose of this work was to evaluate some new filtration systems in relation to the quality of extra-virgin olive oil (EVOO). Filtration processes were undertaken using a polypropylene filter bag and two different inert gas flows as filter aids (argon and nitrogen). Qualitative and quantitative variations of the glyceride composition, antioxidant and pro-oxidant compounds, and water content were correlated with the oxidative stability to establish the effect on EVOO shelf life. The influence on physicochemical and sensorial properties was also evaluated. After filtration, the oxidative stability was reduced. The behavior of the polyphenols and water content on the filtration process could explain the lowest oxidative stability of filtered EVOO. Moreover, the results of the sensorial analysis confirmed that filtration using inert gases did not decrease the intensity of the main positive sensory attributes. The results could help olive-oil producers to improve EVOO quality and establish optimal storage conditions.