Nuclear magnetic resonance analysis of extra virgin olive oil: classification through secoiridoids.

BACKGROUND: Extra virgin olive oil (EVOO), a natural product with a multidisciplinary role, has been and is continuing to be studied from several points of view. Among them, its chemical analysis is of major importance and several methods have been used. Nuclear magnetic resonance (NMR) spectroscopy has inherent advantages, among them monitoring the chemical constituents without the need for a separation technique and without, for instance, possible carry-over effects. Additionally, several magnetic resonance spectroscopic techniques can provide a novel powered insight into the nature and properties of a sample under study. Moreover, -omics procedure can reveal new information and can lead to the classification of populations under study. The main objective of the present work was the possible classification of the EVOO samples based on their aldehyde content using a proposed unreferenced 1 H-NMR spectroscopic quantification method combined with a metabolomic approach. Moreover, the study of the impact of such elevated aldehyde content on several spectra regions of importance in the proton NMR spectra led to the proposal of a possible new isomer indicator. RESULTS: Univariate analysis of 12 EVOO samples showed that oleacein, oleocanthal, elenolic acid, hydroxytyrosol/hydroxytyrosol derivatives and tyrosol/tyrosol derivatives strongly differentiated two classes of EVOO: OEH (for high aldehyde EVOO content) and OE (for non-high aldehyde content). Moreover, we pointed out the 'impact' of such elevated secoiridoid and derivatives content, through their moieties' units, on a range of several resonances of the 1 H-NMR spectrum. The metabolomic approach demonstrated the classification of EVOO samples based on their secoiridoid and derivatives content. Multivariate analysis showed a strong influence on the discrimination of the EVOO classes based on the protons resonating at the aldehyde region of the 1 H-NMR spectrum; the aldehyde protons corresponding to 5S,4R-ligstrodial and 5S,4R-oleuropeindial, oleacein, oleocanthal, elenolic acid, p-HPEA-EA, 3,4-DHPEA-EA, 5S,4R- and 5S,4S-ligstrodial and the proton corresponding to a new compound were reported for the first time. This isomer compound, reported for the first time, could serve as a possible indicator for EVOO classification. CONCLUSIONS: An unreferenced quantification method was proposed and EVOO samples were classified into two classes: OEH and OE, according to their aldehyde content, gaining thus probably higher nutrient and possible pharmacological value. Moreover, we point out the 'impact' of such elevated aldehyde content on several spectral regions of the 1 H spectrum. Finally, a new compound was detected in the OEH samples and is reported for the first time. This compound could possibly be an indicator. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Development of Enriched Oil with Polyphenols Extracted from Olive Mill Wastewater.

The extraction of olive oil produces significant residual olive-mill wastewater (OMW). The composition of OMW varies according to the type of olive, the fruit's ripeness level, and the extraction method (traditional one-pressing system or continuous systems based on centrifugation of the olive pulp). In olive-producing countries, OMW is important for the environment and the economy and is also a low-cost source of polyphenolic compounds with high antioxidant properties. Olive oil's properties, such as its anti-atherogenic, anti-inflammatory, anti-aging, and immunological modulator effects, have been attributed to its polyphenols. In this study, the cloud point extraction (CPE) method was used to recover polyphenolic compounds from OMW. The total micellar phase of the three recoveries was 24.2% and the total polyphenols (after sonication) was 504 mg GAE/Kg. Furthermore, the addition of polyphenols recovered from OMW enhanced the olive oil and extended its shelf life without changing its organoleptic properties. There was a 42.2% change in polyphenols after 0.5% enrichment of micellar dispersions. Thus, it is suggested that the CPE method could lead to better waste management in the olive oil industry and improve the nutritional quality of food products.

Kappa-casein based electrochemical and surface plasmon resonance biosensors for the assessment of the clotting activity of rennet.

We report for the first time the development of kappa-casein (κ-CN)-based electrochemical and surface plasmon resonance (SPR) biosensors for the assessment of the clotting activity of rennet. Electrochemical biosensors were developed over gold electrodes modified with a self-assembled monolayer of dithiobis-N-succinimidyl propionate, while SPR measurements were performed on regenerated carboxymethylated dextran gold surfaces. In both types of biosensor, κ-CN molecules were immobilized onto modified gold surfaces through covalent bonding. In electrochemical biosensors, interactions between the immobilized κ-CN molecules and chymosin (the active component of rennet) were studied by performing cyclic voltammetry, differential pulsed voltammetry, and electrochemical impedance spectroscopy (EIS) measurements, using hexacyanoferrate(II)/(III) couple as a redox probe. κ-CN is cleaved by rennet at the Phe105-Met106 bond, producing a soluble glycomacropeptide, which is released to the electrolyte, and the positively charged insoluble para-κ-casein molecule, which remains attached to the surface of the electrode. This induced reduction of the net negative charge of the sensing surface, along with the partial degradation of the sensing layer, results in an increase of the flux of the redox probe, which exists in the solution, and consequently, to signal variations, which are associated with the increased electrocatalysis of the hexacyanoferrate(II)/(III) couple on the gold surface. SPR experiments were performed in the absence of the redox probe and the observed SPR angle alterations were solely attributed to the cleavage of the immobilized κ-CN molecules. Various experimental variables were investigated and under the selected conditions the proposed biosensors were successfully tried to real samples. The ratios of the clotting power units in various commercial solid or liquid samples, as they are calculated by the EIS-based data, were almost identical to those obtained with a reference method. In addition, EIS measurements showed an excellent reproducibility, lower than 5%.

Impedimetric biosensor for the assessment of the clotting activity of rennet.

Cheese production is relied upon the action of rennet (a mixture of chymosin and pepsin) onto casein micelles of milk. For the first time, the monitoring of this interaction with electrochemical impedance spectroscopy (EIS) was used to develop a faradic impedimetric biosensor for the assessment of the clotting activity of rennet, using hexacyanoferrate(II)/(III) couple as a redox probe. Gold electrodes were modified with self-assembled monolayers of different thiols (thioctic acid, dithiobis-N-succinimidyl propionate, and cysteamine), and (artificial) casein micelles were immobilized on the modified gold surfaces. The proposed method is based on the measurement of charge-transfer resistance (R(ct)) changes attributed to the degradation of the negatively charged immobilized casein micelles by rennet to neutral biostructures. This action results in the increase of the flux of the redox probe, which exists in the bulk solution, to the surface of the electrode and, consequently, in the decrease of R(ct). Experimental parameters such as the micelle loading, the reaction time, the concentration of rennet, and the working pH, were optimized. Besides EIS measurements, cyclic voltammetry, FT-IR, and atomic force microscopy (AFM) experiments were also performed before and after the interaction of the immobilized micelles with rennet. Finally, the proposed biosensors were successfully tried for various commercial samples.

Decrease of heat shock protein levels and cell populations by wine phenolic extracts.

The effect of red and white wine total extracts and phenolic fractions on heat shock protein (Hsp) levels in tumor cells and on tumor and endothelial cell populations in vitro has been investigated. Total extracts of red wines decreased Hsp70 and Hsp27 levels and the numbers of tumor and endothelial cells. Several red and white wine fractions significantly decreased Hsp27 levels, and some of them had also an effect on Hsp70 levels. A red wine fraction rich in polymeric flavanols and a white wine one rich in phenolic acids, flavonols, and tyrosol strongly lowered Hsp27 levels. Some red and white wine fractions strongly reduced tumor cell numbers, whereas most of them decreased endothelial cell numbers to variable extents. The present results indicate that wine phenolics decrease Hsp levels in tumor cells and tumor and endothelial cell populations. These properties may be important in the potent anticarcinogenic action of wine phenolics.