A multivariate study of the relationship between fatty acids and volatile flavor components in olive and walnut oils

The relationships between FA and the volatile profiles of olive and walnut oils from Argentina were studied using GC and solid-phase microextraction coupled with GC-MS. The major volatiles were aldehydes and hydrocarbons, produced mainly through the oxidative pathways. n-Pentane, nonanal, and 2,4-decadienal were predominant in walnut oils, whereas nonanal, 2-decenal, and 2-undecenal were the most abundant components in olive oils. A multivariate analysis applied to the chemical data emphasized the differences between the oils and allowed us to see a pattern of covariation among the FA and the volatile compounds. The main differences between walnut and olive oils were the presence of larger amounts of short-chain (C₅–C₆) saturated hydrocarbons and aldehydes in the former and the greater quantities of medium-chain (C₇–C₁₁) compounds in olive oil. This can be explained by their different origins, mainly from the linoleic acid in walnut oil or almost exclusively from the oleic acid in olive oil.     

Use of chlorophyll and carotenoid pigment composition to determine authenticity of virgin olive oil

The chlorophyll and carotenoid pigment profile of 50 mono-variety virgin olive oils was used to develop an index of authenticity for the product. The presence of carotenoids other than those described, or chlorophyll derivatives at another level of degradation, were found to be determing elements of this index for “virgin” olive oil quality. In addition, the ratio of chlorophyll/carotenoid should be around 1, and the ratio of minor carotenoids/lutein should be about 0.5, with a limited variability. These characteristics may be expected of virgin olive oil in general and are independent of variety. Finally, the percentage of lutein, violaxanthin, and total pigment content may be used to distinguish between mono-variety virgin olive oils.     

Determination of olive oil free fatty acid by fourier transform infrared spectroscopy

A new procedure for determining free fatty acids (FFA) in olive oil based on spectroscopic Fourier transform infrared-attenuated total reflectance spectroscopy measurements is proposed. The range of FFA contents of samples was extended by adding oleic acid to several virgin and pure olive oils, from 0.1 to 2.1%. Calibration models were constructed using partial least-squares regression (PLSR). Two wavenumber ranges (1775–1689 cm⁻¹ and 1480–1050 cm⁻¹) and several pretreatments [first and second derivative; standard normal variate (SNV)] were tested. To obtain good results, splitting of the calibration range into two concentration intervals (0.1 to 0.5% and 0.5 to 2.1%) was needed. The use of SNV as a pretreatment allows one to analyze samples of different origins. The best results were those obtained in the 1775–1689 cm⁻¹ range, using 3 PLSR components. In both concentration ranges, at a confidence interval of α = 0.05, no significant differences between the reference values and the calculated values were observed. Reliability of the calibration vs. stressed oil samples was tested, obtaining satisfactory results. The developed method was rapid, with a total analysis time of 5 min; it is environment-friendly, and it is applicable to samples of different categories (extra virgin, virgin, pure, and pomace oil).     

Effect of extraction systems on the quality of virgin olive oil

Research has been carried out to ascertai the effects of different processing systems on olive oil quality. Tests were performed in industrial oil mills that were equipped with both pressure and centrifugation systems. Results show that oils extracted from good-quality olives do not differ in free fatty acids, peroxide value, ultraviolet absorption and organoleptic properties. Polyphenols ando-diphenols contents and induction times are higher in oils obtained from good-quality olives by the pressure system because it does not require addition of water to the olive paste. The centrifugation system requires the addition of warm water to the olive paste and helps to obtain oils with a lower content of natural antioxidants. Oils obtained from poorquality or from ripe olives in continuous centrifugal plants are lower in free fatty acids than those obtained by the pressure system. Dr. Mario Solinas is deceased—May 23, 1993.     

Pigment parameters determining spanish virgin olive oil authenticity: Stability during storage

The chlorophyll and carotenoid pigment composition in 12 mono-variety virgin olive oils was examined every 30 d during 1 yr of storage at 15°C in darkness. The oil authenticity parameters, as defined by the ratio of chlorophylls/carotenoids and the ratio of minor carotenoids/lutein, remained stable throughout storage, irrespective of the variety and degree of ripeness of the source fruit. The percent of violaxanthin, percent of lutein, and total pigment content, the classifying variables chosen as the best possible discriminators among olive varieties, also remained stable during storage. The prediction model for olive variety, which was based on a discriminant multivariate analysis of the observed values of these variables, gave a correct classification in 99.6% of the oils analyzed. The discriminant criterion established remained valid after 1 yr of oil storage. The detection of chlorophyll derivatives other than those associated with the physical extraction process was seen as a quality index, as small, analytically detectable transformations in the structure of pigments were indicative of oil storage.     

Influence of ecological cultivation on virgin olive oil quality

The quality of oil extracted from ecologically cultivated olives of the Picual variety was compared with oil extracted from Picual olives cultivated using conventional methods. Olive trees were grown in a two-section plot. Fruits from each plot were harvested at various stages of ripeness, and acidity value, peroxide index, ultraviolet absorption at 232 and 270 nm, stability to oxidation, sensory analysis, fatty composition, and contents of tocopherols, phenolic compounds, and sterols were determined on oil extracted from each treatment. The results showed that the organic virgin olive oil was of a superior quality to the conventional virgin olive oil in all the quality parameters analyzed.     

A high-field1H nuclear magnetic resonance study of the minor components in virgin olive oils

High-field (600 MHz) nuclear magnetic resonance (NMR) spectroscopy was applied to the direct analysis of virgin olive oil. Minor components were studied to assess oil quality and genuineness. Unsaturated and saturated aldehyde resonances, as well as those related to other volatile compounds, were identified in the low-field region of the spectrum by two-dimensional techniques. Unsaturated aldehydes can be related to the sensory quality of oils. Other unidentified peaks are due to volatile components, because they disappear after nitrogen fluxing. The statistical analysis performed on the intensity of these peaks in several oil samples, obtained from different olive varieties, allows clustering and identification of oils arising from the same olive variety. Diacylglycerols, linolenic acid, other volatile components, water, acetic acid, phenols, and sterols can be detected simulteneously, suggesting a useful application of high-field NMR in the authentication and quality assessment of virgin olive oil.     

Use of nitrogen to improve stability of virgin olive oil during storage

Experiments were carried out to study the possibility of improving the stability of extra virgin olive oil by using nitrogen as a conditioner gas during storage. With this aim, virgin olive oil samples, obtained from Leccino and Coratina cultivars, were stored in the dark, in closed bottles conditioned with air or nitrogen at 12–20 and 40°C. Results indicated that the FFA percentage increased over 1% only when oils were stored at 40°C. The PV and the K ₂₃₂ value (light absorbance at 232 nm) of oils increased over the limit value allowed by European Union law when the bottles were only partly filled and air was the conditioner gas. The use of nitrogen as conditioner gas helped to avoid this risk during 24 mon of storage at 12–20°C. The total phenolic content of both cultivars oils decreased during storage because their oxidation protected the oils from autoxidation. The content of total volatile compounds in oils decreased continuously during storage at 12–20°C, whereas it increased over 10 (Coratina cv.) and 15 (Leccino cv.) mon and then diminished when the storage temperature was 40°C. The same behavior, i.e., increase then decrease, was ascertained for trans-2-hexenal. The hexanal content of oils increased continuously during storage because this compound is formed by the decomposition of the 13-hydroperoxide of linoleic acid.