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.     

Influence of seasonal conditions on the composition and quality parameters of monovarietal virgin olive oils

The aim of this work was to determine the effect of the climatological conditions of the olive crop season on the composition of monovarietal virgin olive oils obtained from the Arbequina cultivar with special emphasis on the phenolic fraction, its percent distribution, and related oil quality parameters such as oxidative stability and bitter index. The main differences were due to freeze injuries caused by low temperatures in December 2001. The levels of chlorophylls and carotenoids in olive oil or pulp from frost-damaged olive trees were lower as a consequence of faster ripening. The olive oil extracted from frost-damaged olive pulp had lower contents of secoiridoid and especially lower levels of 3,4-DHPEA-EDA (the dialdehydic form of elenolic acid linked to hydroxytyrosol). In the following crop seasons, a significant increase in phenolic compounds, especially in secoiridoid derivatives such as 3,4-DHPEA-EDA, was observed. This increase may be due to the fact that olive trees that suffered frost damage in December 2001 were more sensitive to stress caused by the water deficit during summer in the subsequent crop seasons, which is usual in this olive-growing region. Moreover, important correlation coefficients were observed between the main secoiridoid derivative compound (3,4-DHPEA-EDA) and oxidative stability and the bitter index.     

Profile of enzyme in drupe of oueslati's cv. olives during ripening phases: A support method implementation in the production of extra virgin olive oil

Quality of virgin olive oil (VOO) depends on phenolic molecules content, which depends on the biochemical characteristics of olive fruits, namely endogenous enzymes. In order to ascertain the influence of olive fruit ripening degree on the phenol content, enzyme activities in olive fruits, and the quality of the corresponding oils were studied during Oueslati olive ripening. In fact, three enzymes were studied: peroxidase (POX) in olive seeds, polyphenoloxidase (PPO), and β-glucosidase (β-GL) in olive fruits mesocarp. Each enzyme showed specific trend: POX activity increased gradually until reaching a maximum (17.061 ± 0.101 U g⁻¹ FW) at ripening index (RI) 3.6 and then decreased slowly at advanced ripening stage. However, the maximum of PPO activity (240.421 ± 0.949 U g⁻¹ FW) was observed earlier at RI of 0.7. Concerning β-glucosidase activity, its maximal was 60.857 ± 1.105 U g⁻¹ FW at RI 2.8, then, it decreased sharply to reach 17.096 ± 0.865 U g⁻¹ FW at RI 3.9. A significant increase of total phenol content as well as the antioxidant activity were observed during Oueslati olive ripening. Moreover, phenolic profile indicated that appropriate harvesting date of Oueslati olives coincided with RI 3.9 given that highest content of most important individuals phenolic compounds responsible for the main VOO biological properties achieved on this date. Furthermore, phenols amount of Oueslati VOO was principally due to PPO enzyme activity as the increase in total phenols coincides with the decrease in PPO activity.     

Characteristics and sensory assessment of extra virgin olive oils produced in two different zones of Brazil

The Brazilian olive oil production has been growing in recent decades and largest plantations are on two different zones, from Serra da Mantiqueira (states of Minas Gerais and São Paulo) and Campanha Gaúcha (state of Rio Grande do Sul). The total planted area, in 2022, reached approximately 6500 hectares. The aim of the present study was to characterize the sensory and analytical parameters of extra virgin olive oils (EVOO) from Southwestern (Serra da Mantiqueira) and Southern (Campanha Gaúcha) Brazil regions. Twenty-two EVOO samples were obtained from different cultivars of unlike regions. Quality parameters, oxidative stability, phenolic compounds ortho-diphenols and fatty acids were analyzed and relationships with olive variety or region. From the chemical perspective, the EVOO exhibited all parameters within the necessary to be qualified as extra virgin, according to international standard definitions. All samples showed a good quality of sensory perceptions and a high level of polyphenols, which are varied among samples but was more intense in Campanha Gaúcha olive oils.     

Susceptibility of water-emulsified extra virgin olive oils to oxidation

The effect of emulsion structure on the susceptibility to oxidation of emulsified olive oils was tested. Olive oil samples were emulsified by adding a certain quantity of water in different ways. The resulting water-in-oil emulsions were then oxidized with UV light. The results revealed that the emulsion structure played a significant role in the oxidation process of emulsified olive oils. A kinetic mechanism is discussed based on the PV determined experimentally. The susceptibility of water-emulsified extra virgin olive oils to oxidation was quantified by means of a dimensionless parameter that displayed a characteristic dependence on the specific surface area of the water dispersed phase.     

Effects of the cold percolation system on the quality of virgin olive oil

The effects of the cold percolation system on the quality of virgin olive oil from two different Italian cultivars (Coratina and Oliarola) were determined. The quality was also compared with that of oil extracted with the current centrifugation system using a two‐phases decanter. Tests were performed in an industrial oil mill equipped with the two extraction systems. The oils extracted with cold percolation system showed, in all cases, lower free acidity, peroxide value, and ultraviolet (UV) absorption (K₂₃₂ and K₂₇₀) and higher polyphenol contents in comparison to oils obtained by two‐phases centrifugation. These results were confirmed by the autoxidation stability of the oils examined.     

Evaluation of the bitter taste in virgin olive oil

An analytical method has been developed to evaluate the intensity of the bitter taste in virgin olive oil. Results from the proposed method, based on extraction of the bitter constituents of virgin olive oil with methanol/water and measurement of the absorbance at 225 nm, show a significant correlation with the intensity of bitterness that had been evaluated in a sensorial manner by a panel. The developed method, therefore, offers a real alternative to the panel test for the evaluation of this attribute.     

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.     

Low molecular weight polypeptides in virgin and refined olive oils

Twenty-eight virgin olive oils—from different regions of Spain and prepared from olive drupes of different varieties—and six refined olive oils were analyzed to determine the presence of proteins in these oils. All oils studied showed the presence of proteins in the range of 7–51 μ/100 g of oil. There were no significant differences in protein content in oils from different varieties or between virgin or refined oils. In addition, all oils exhibited analogous amino acid patterns, suggesting a similarity among protein fractions obtained from different oils. A polypeptide with an apparent M.W. of 4600 Da was common to the isolated protein fractions. These results suggest that this polypeptide is a previously unknown minor component in olive oils. No clear influence of this component on oil stability was observed when oil stabilities were estimated as a function of phenol, tocopherol, phosphorus, and protein contents of the oils.     

Effect of extraction system, stage of ripeness, and kneading temperature on the sterol composition of virgin olive oils

Comparative extraction trials were carried out among a classical pressing, a dual-, and a three-phase centrifugation system using olive crops of Koroneiki variety. Two different kneading temperatures, 30 and 45°C, were tested at three stages of ripeness for two consecutive years of harvest, 1995–1996 and 1996–1997. Composition of the sterol fraction was determined in the resulting olive oil samples (n=72). Stigmasterol was found to be affected by the extraction system; it was obtained in the highest amount in the pressing system. The ratio campesterol/stigmasterol was significantly higher in oils extracted by dual- and three-phase centrifugation. Sterols were significantly affected by the ripening stage of the fruit. During December, the ratio campesterol/stigmasterol reached the maximal and β-sitosterol the minimal values; this appears to be the optimal period for harvesting the olives. Comparison of the different kneading temperatures showed that at 30°C, Δ⁵-avenasterol and campesterol/stigmasterol ratio reached higher values than at 45°C.     

Evolution of thermograph parameters during the oxidation of extra virgin olive oil

The modulated differential scanning calorimetry (M‐DSC) was used as a rapid and effective method to characterize the olive oil at different levels of oxidation. Thermograph parameters have been related to oxidative degradation of the triglycerides. In this study, their relation to the characteristic off‐flavor compounds, correlated to the oxidative degradation of the oil, was also investigated. Extra virgin olive oil samples were subjected to the following oxidation treatments: a) purged with air using glass washing bottles at two flow rate values, b) heated in a conventional oven at two area/oil mass ratios, and c) heated in a microwave oven also at two area/oil mass ratios. Samples were withdrawn and analyzed at predetermined intervals. Flavor and off‐flavor compounds were isolated using a dynamic thermal stripping apparatus and transferred into a gas chromatograph by using a thermal desorption unit. All oil samples were analyzed by M‐DSC during cooling from 25 °C to ?60 °C at 7 °C/min, and heating back to 40 °C at 10 °C/min. High correlation values were obtained between various M‐DSC thermograph parameters and certain volatile compounds. Results showed that M‐DSC could be used as a simple method to indicate compositional changes in olive oil during oxidation.     

Chromatic evolution of virgin olive oils submitted to an accelerated oxidation test

Six samples of virgin olive oil obtained from several varieties of olive fruits (Picual, Manzanilla, Lechín, and Arbequina) were submitted to an accelerated oxidation process during a 63-h period under the conditions of the oil stability index (OSI), as measured by a Rancimat (100°C) apparatus. Spectra were measured every 3 h, and chlorophyll and carotenoid indexes and CIFLAB color ordinates were calculated. As oxidation time increased, remarkable changes in the spectral characteristics and color ordinates were observed. Oxidation provoked less vivid colors (lower values for chroma, C _* ^ab ) in all the samples; however, only some varieties became darker (lower values for lightness, L^*). The pigment loss calculated for oxidized oils was 67% for the carotenoid index and 58% for the chlorophyll index. Mathematical models are offered to predict color changes with time of storage at 20°C.     

Natural antioxidants and volatile compounds of virgin olive oils obtained by two or three‐phases centrifugal decanters

Research has been carried out to ascertain the influence of different centrifugal decanters employed in olive process on oil yields and qualitative characteristics and composition of volatile compounds of virgin olive oil. Tests were performed in an olive oil mill equipped with centrifugal decanters at two or three‐phases. Results show that oil yields were similar and oils extracted from good‐quality olives do not differ in free fatty acids, peroxide value, UV absorptions and organoleptic assessment. Total phenols and o‐diphenols content as well as induction time values are higher in oils obtained by the centrifugal decanter at two‐phases, because it requires less quantity of water added to olive paste in comparison to the three‐phases centrifugal decanter. The amount of water added determines the dilution of the aqueous phase and lowers the concentration of the phenolic substances more soluble in vegetable waste water. Due to the partition equilibrium law the concentration of the same substances consequently diminishes in the oil. In this research, the coefficient of the partition equilibrium of total phenols between oil and vegetable water has been calculated and discussed. No significant difference occurred, due to the different decanters employed, in the average values of the volatile components of the head‐space of oils.     

Effect of growing area on pigment and phenolic fractions of virgin olive oils of the arbequina variety in Spain

The purpose of this investigation was to study differences in the chlorophyll, carotenoid, and phenolic fractions of virgin olive oils from the Arbequina variety cultivated in different olive growing areas of Spain. Virgin olive oil from Lleida was less heavily pigmented, and these oils showed more negative values for the ordinate a^* (of the CIELAB colorimetric system). Pheophytin a was the major chlorophyll pigment, and lutein was the major component of the carotenoid fraction in all oils analyzed. The chlorophyll a concentration in virgin olive oils from Lleida was 700 μg kg⁻¹, but was 175 μg kg⁻¹ in oils from Jaén, and 200 μg kg⁻¹ in oils from Tarragona. Finally, the chlorophyll a/chlorophyll b ratio was 9 in oils from Lleida and around 0.6 in the other two Arbequina olive oils. In relation to the phenolic fraction, the hydroxytyrosol and tyrosol contents were significantly higher in olive oils from Jaén (grown at higher altitude and precipitation rates). The secoiridoid derivatives showed a significantly higher concentration in olive oils from Tarragona, probably due to the low altitude where they grow, and finally the ratio of (dialdehydic form of elenolic acid linked to tyrosol)/lignans had a value of 1.4 in olive oils from Lleida, whereas this value was around 0.7 in the other Arbequina olive oils.     

Reliability of the bromthymol blue method for color in virgin olive oils

The bromthymol blue (BTB) method is currently used for the assessment of color in olive and seed oils by visual comparison with standard solutions. Two BTB scales were prepared with 2 yr difference and compared, and the recent one was used to analyze 502 virgin olive oil samples, obtained by the Abencor® technique reproducing the industrial procedure. The temporal chromatic degradation of the BTB samples after 2 yr [3.93 Commission Internationale de l’Eclairage (CIE) 1976-(L*a*b*) (CIELAB) units, on the average], as well as the small percentage of virgin olive oils matching the colors of the samples provided by the BTB scales (13.1% with a suprathreshold color tolerance of 1.52 CIELAB units), indicates the limitations of the BTB method. Linear regression models are proposed in order to compute with acceptable accuracy the BTB indices from chromaticparameters. The use of CIELAB for the specification and future studies on color in virgin olive oils is recommended.     

Influence of the type of olive‐crusher used on the quality of extra virgin olive oils

An experimental investigation was carried out to evaluate the quality of virgin olive oils obtained when either a hammer‐crusher or a disk‐crusher were used for the olive paste preparation; the effect of the temperature rise caused by rapid olive crushing was also assessed. Oxidative degradation in the oils obtained from hammer‐crushed olives was significantly higher than in those obtained from disk‐crushed olives as shown by the levels of oxidised triacylglycerols and the results of the oven test. A significant inverse correlation (p <0.001) was found between the Rancimat induction time values and the amounts of oxidised triacylglycerols as determined by the high‐performance size exclusion chromatography analysis of polar compounds. These findings suggested that polar compound analyses, just as routine analyses, may be used as a suitable analytical tool to effectively evaluate the quality of virgin olive oils.     

Effect of extra virgin olive oil on glycaemia in healthy young subjects

In this approach we studied the glycaemia levels in 20 healthy young volunteers (26 ± 2 years), before and after a 30‐day intake of 50 mL of extra virgin olive oil (EVOO). We selected an oil rich in phenolic compounds (523 mg/L) with a high content of secoiridoidic derivatives (over 94.5%). The findings from our study reveal a significant decrease of glycaemia from 89.6 ± 6.8 to 82.7 ± 10.3 mg/dL (p<0.05), related to a long term daily intake of the study EVOO, as the only added fat. A significant increment of the HDL cholesterol, from 68.7 ± 11.5 to 75.2 ± 4.9 mg/dL, was also highlighted. Total cholesterol, LDL, VLDL, triglycerides, and blood pressure did not show significant variation after the 30‐day consumption of this EVOO. So far, few articles have described the influence of EVOO consumption, on plasma glucose levels in humans. This effect is observed in a group of healthy young humans. Moreover, we confirm that the level of free hydroxytyrosol (OH‐Tyr) in plasma increased up to fourfold (p<0.05) after the 30‐day intake of this EVOO. In addition, the excretion in urine of the main metabolite of OH‐Tyr, homovanillic acid (HVA), significantly increased.     

A rapid estimation of pigment content in virgin olive oils by a solvent-free method

In this work, a fast method was proposed for estimating the virgin olive oils (VOOs) carotenoids and chlorophylls concentration using color measurement. The pigment content by conventional spectrophotometry method and CIELAB color (L*, a*, and b*) at different degree of sample thickness (from 5 to 50 mm) of one hundred VOOs were measured. Oil carotenoids and chlorophylls content were correlated with the color parameters for the different oil thickness studied to design the prediction models of the new method. The best regression coefficients (R²) were obtained for multiple linear regression model using the three independent variables (L*, a*, and b*) together measured at 5 mm of oil thickness. The R² were 0.9679, 0.9515, and 0.9644 for predicting carotenoids, chlorophylls, and total pigments, respectively. External validation of these prediction models was satisfactory (relative error < 0.1). Therefore, this new solvent-free colorimetric method is a useful method for determination of carotenoids and chlorophylls content in VOOs. Practical applications: The simple colorimetric method developed in this study offers a fast and accurate alternative to current methods published in the literature to estimate the pigment content in VOOs. It is a rapid (less than 1 min) and cheap method, with the advantage of ease of operation, no sample pretreatment and solvent-free, thus environmentally friendly. This methodology can potentially be used by trained “nonprofessional analytical skilled” people in small laboratories or olive oil mills with limited technical facilities. Therefore, the technique is highly plausible as an alternative to determine the pigment content in VOOs. Finally, future works with this methodology could be carried out to online control of VOOs pigments content in the oil extraction process.     

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.     

Characterization of virgin olive oil from Southern Tunisia

Fruits from three Tunisian cultivars of Olea europea L. grown in the southeast of Tunisia were harvested at the maturity stage of ripeness and immediately processed with a laboratory mill. There are as yet no data on the chemical composition of virgin olive oils from the southeast of Tunisia, an area characterized by an arid condition of growth for olive trees. Our results showed significant differences in the analytical parameters examined for the three cultivars such as fatty acid composition, total phenols and o‐diphenols, and the content of chlorophylls and carotenoids, confirming the importance of genetic factors in the chemical characteristics of the oil. Headspace solid‐phase microextraction (HS‐SPME) was applied to the analysis of volatile compounds of virgin olive oils. Forty‐eight compounds were isolated and characterized by GC‐RI and GC‐MS, representing 94.1–98.1% of the total amount. (E)‐Hex‐2‐enal, the main compound extracted by SPME, characterized the olive oil headspace for all samples. So, it was clearly shown that there were qualitative and quantitative differences in the proportion of volatile constituents from oils of the various cultivars.