Gradual Changes of the Protective Effect of Phenols in Virgin Olive Oils Subjected to Storage and Controlled Stress by Mesh Cell Incubation.

The oxidation reactions that take place in virgin olive oil under moderate conditions involved the combined effect of antioxidant and prooxidant compounds. Given the complexity of oxidation processes of multicomponent matrices, there is still a need to develop new methods with a dynamic approach to study the persistence of the compounds with healthy properties. This work studied the joint evolution of them, including phenols and pheophytin a, modeling their tendency during a real storage. The regression equations performed with the total phenol concentration showed that around 2% of the concentration was lost every month. Simultaneously, the progress of oxidation was evaluated by mesh cell incubation and Fourier transform infrared analysis. This method pointed out that, in the presence of light, the prooxidant effect of pigments was able to mask the protective effect of phenols, until the pheophytin a concentration was lower than 1 mg/kg. The antioxidant effect of phenols was less remarkable when the concentration loss was 35% or more.

PhotooxidationEffect in Liquid Lipid Matrices: Answers from an Innovative FTIR Spectroscopy Strategy with "Mesh Cell" Incubation.

Developing new approaches to evaluate the stability of edible oils under moderate conditions is highly demanded today to avoid accelerated experiments that are not well correlated with actual shelf life. In particular, low intensity of visible light (photooxidation) needs to be integrated in stability studies, together with mild temperature. Thus, in this work, a strategy based on a "mesh cell"-FTIR to monitor chemical changes in lipid matrices using a combination of light and mild heating was applied. The results were compared with those obtained for the stability of triolein used as a molecular model. The study showed that the moderate light intensity (400 lx) at a low temperature (23 °C) has an early effect on the degradation of lipid matrices that is not observed when they are stored at 35 °C in the absence of light. Thus, the results proved that the exposure to light (400 lx) was more relevant than mild heating (35 °C) in monounsaturated lipid matrices, while polyunsaturated lipid matrices were more sensitive to mild heating.

In-depth assessment of analytical methods for olive oil purity, safety, and quality characterization.

This paper evaluates the performance of the current analytical methods (standard and widely used otherwise) that are used in olive oil for determining fatty acids, triacylglycerols, mono- and diacylglycerols, waxes, sterols, alkyl esters, erythrodiol and uvaol, tocopherols, pigments, volatiles, and phenols. Other indices that are commonly used, such as free acidity and peroxide value, are also discussed in relation to their actual utility in assessing quality and safety and their possible alternatives. The methods have been grouped on the basis of their applications: (i) purity and authenticity; (ii) sensory quality control; and (iii) unifying methods for different applications. The speed of the analysis, advantages and disadvantages, and multiple quality parameters are assessed. Sample pretreatment, physicochemical and data analysis, and evaluation of the results have been taken into consideration. Solutions based on new chromatographic methods or spectroscopic analysis and their analytical characteristics are also presented.

Time course analysis of fractionated thermoxidized virgin olive oil by FTIR spectroscopy.

FTIR spectroscopy has been used to examine the spectral changes taking place in the polar fraction of thermoxidized virgin olive oil and compared to those changes occurring in the neat oil and the nonpolar fraction. It was demonstrated that examination of the polar fraction provides additional and substantially better information of the chemical changes taking place as oxidation proceeds because this fraction concentrates the oxygenated compounds formed. Of particular interest is the enhancement of the OH component of the spectrum (3600-3200 cm(-1)) as well as tertiary alcohol formation (~1167 cm(-1)), including the region associated with epoxides. Time course spectral changes for neat virgin olive oil and its polar and nonpolar fractions are illustrated, compared, and contrasted, demonstrating that the interpretation of neat oil spectra is greatly enhanced by fractionation and may in fact be a preferred means of studying thermoxidation processes.

Quality characterization of the new virgin olive oil var. Sikitita by phenols and volatile compounds.

New cultivars with greater adaptability to modern irrigated (super-) high-density orchards and producing good sensory quality oils are highly demanded by an olive oil industry in continuous change. This work analyzes olive oil sensory quality, in terms of phenols and volatiles that are responsible for virgin olive oil flavor, for three cultivars: Picual, which is used for >15% of world olive oil production; Arbequina, which is cultivated worldwide; and the new progeny Sikitita, which is derived from the other two. The availability of data at three different levels of ripeness allowed quantifying the genetic and olive maturity effects on the oil composition by means of the analysis of variance (ANOVA) and principal component analysis (PCA). Phenols and volatiles varied greatly both with genotype and, to a lesser extent, with olive maturity. With regard to the phenol profile, the crossbred cultivar Sikitita showed a higher degree of similarity with the Arbequina variety. The volatile composition of var. Sikitita, however, varies significantly from that of Arbequina, in the first stages of the olive ripeness, and becomes more similar to that of Picual as the level of ripeness increases.

Evaluation of virgin olive oil thermal deterioration by fluorescence spectroscopy.

The evolution of the fluorescent compounds during the thermal deterioration of virgin olive oil is not yet well-known. Samples of heated virgin olive oils collected from a fryer every 2 h up to 94 h were analyzed to study their fluorescence spectra as well as the evolution of the concentrations of alpha-tocopherol and individual phenols by high-performance liquid chromatography (HPLC). The regions of the fluorescence spectra of the heated oils, diluted in hexane at 1%, were explained by the content of these compounds with regression coefficients higher than 0.90 (R2 adjusted). The fluorescence intensity recorded at 350 nm and the wavelength of the spectrum maximum in the range of 390-630 nm also allowed for the explanation of the increase of the percentage of polar compounds during the experiment. On the other hand, the spectra of the undiluted heated oils indicated that the maximum of the spectrum of any undiluted oil at 490 nm or beyond is related to a percentage of the polar compounds higher than 25%, which is the maximum percentage accepted for edible oils used in frying processes.

Thermal deterioration of virgin olive oil monitored by ATR-FTIR analysis of trans content.

The monitoring of frying oils by an effective and rapid method is one of the demands of food companies and small food retailers. In this work, a method based on ATR-FTIR has been developed for monitoring the oil degradation in frying procedures. The IR bands changing during frying in sunflower, soybean, and virgin olive oils have been examined in their linear relationship with the content of total polar compounds, which is a preferred parameter for frying control. The bands assigned to conjugated and isolated trans double bonds that are commonly used for the determination of trans content provided the best relationships. Then, the area covering 978-960 cm(-1) was chosen to build a model for predicting polar material content for the particular case of virgin olive oil. A virgin olive oil was heated up to 94 h, and samples collected every 2 h constituted the training set. These samples were analyzed to obtain their FTIR spectra and to determine the composition of fatty acids and the content of total polar compounds. The excellent results predicting the polar material content (adjusted R(2) 0.997) was successfully validated with an external set of samples. The analysis of the fatty acid composition confirmed the relationship between the trans content and the content of total polar compounds.

Volatile compounds characterizing Tunisian Chemlali and Chétoui virgin olive oils.

A total of 33 virgin olive oil samples of the two main Tunisian cultivars, Chemlali and Chétoui, were characterized by their volatile compounds. The olive oil samples were obtained from olives harvested at four stages of ripeness in costal and inland farms of different geographical places. Major volatiles, mostly C6 and C5 compounds produced from linolenic and linoleic acids through the lipoxygenase cascade, were quantified by solid-phase microextraction-gas chromatography. Mathematical procedures allowed for the determination of the volatiles that not only are able to discriminate the olive oils by their olive cultivar (hexanal, E-2-hexenal, and total ketones) and ripeness (pentanal and 1-penten-3-one) but also contribute to their distinctive aroma. Finally, an electronic nose based on metal oxide sensors was checked for a rapid and at-line implementation of Tunisian olive oil varietal traceability. The classification of the samples by the sensors was explained by their sensitivity to volatiles E-2-hexanal, hexanal, 1-penten-3-one, ethanol, and Z-3-hexenol. Multivariate procedures of discriminant analysis and principal component analysis were used in the study.