Color determination in olive oils

Color characterization of olive oil may be of great importance to the industry. To determine the color of a solution, it is necessary to accurately measure a series of tristimulus coordinates for which several methods exist. This study analyzes the errors in the calculation of tristimulus values of olive oil color based on methods, by using several selected ordinates and an increasing number of weighted ordinates, and how these errors affect the values of the chromatic parameters defined in the various chromatic systems. The above analysis shows that the use of a large number of ordinates will lead to better results in the color definition of oils. For its determination, we have used the CIE 1931, CIELUV 1976 and CIELAB 1976 spaces; the latter yields the best results.     

Lipoxygenase activity in olive (Olea europaea) fruit

The present work was designed to characterize lipoxygenase activity in olive fruit pulp, in order to determine its significance in the biosynthesis of virgin olive oil aroma. Lipoxygenase activity has been detected in particulate fractions of enzyme extracts from olive pulp subjected to differential centrifugation. The activity in different membrane fractions showed similar properties, with optimal pH in the range of 5.0–5.5 and a clear specificity for linolenic acid, which was oxidized at a rate double that of linoleic acid under the same reaction conditions. The enzyme preparations displayed very low activity with dilinoleoyl phosphatidylcholine, suggesting that olive lipoxygenase acts on nonesterified fatty acids. The enzyme showed regiospecificity for the Δ-13-position of both linoleic and linolenic acid, yielding 75–90% of Δ-13-fatty acid hydroperoxides. Olives showed the highest lipoxygenase activity about 15 wk after anthesis, with a steady decrease during the developmental and ripening periods. Olive lipoxygenase displayed properties that support its involvement in the biogenesis of six-carbon volatile aldehydes, which are major constituents of the aroma of virgin olive oil, during the process of oil extraction.     

The volatile composition of samples from the blend of monovarietal olive oils and from the processing of mixtures of olive fruits

The volatile fraction deriving from the lipoxygenase pathway of samples obtained by processing olive fruits of 2 cultivars in known proportions was compared with that of samples deriving from the blending of oils extracted from the same cultivars and in the same proportions. The varieties considered for the mixtures were Coratina and Koroneiki, Coratina and Frantoio, and Dritta and Bosana, respectively. The results confirmed that the accumulation of each volatile compound from the lipoxygenase pathway in the monovarietal oils was different and closely dependent on the genetic store of each variety. The concentrations of the mentioned compounds appeared to change in a way proportional to the percent of each monovarietal oil in the samples obtained by blending 2 monovarietal oils. Instead, the oils obtained by processing mixtures of fruits from the 2 corresponding cultivars showed a striking accumulation of volatile compounds, especially of C₆‐compounds, which reached higher concentration at different percentages depending on the cultivars processed.     

Phenolic acid content and sensory properties of two Spanish monovarietal virgin olive oils

In recent years, phenolic acids have received considerable attention as they are essential to olive oil quality and nutritional properties. This study aims to validate a rapid and sensitive method based on ultra‐performance liquid chromatography/time‐of‐flight mass spectrometry (UPLC–TOF‐MS) for analyzing the phenolic acid content of olive oil and assessing its impact on virgin olive oil (VOO) sensory attributes. Once this method was validated, we used it to evaluate the phenolic acid composition of several Spanish monovarietal virgin olive oils in relation to nine different olive ripening stages. The results obtained confirm that the methodology developed in this study is valid for extracting and analyzing phenolic acids from VOO. The phenolic acid content of the virgin olive oils sampled was proven to be influenced by the type of cultivar and olive harvest date. Therefore, phenolic acids might be used as potential markers for olive oil cultivar or ripening stage. Finally, the data obtained indicate that the sensory properties of VOO may be differently affected by its phenolic acid content depending on the type of cultivar. Practical applications: The method validated in the present study – based on UPLC‐TOF‐MS – allows experts to assess the phenolic acid content of different VOO cultivars (varieties). This application will probably be very useful to the olive oil industry. The reason is that our study revealed that phenolic acids have an impact on the sensory quality of VOO, which is essential to consumer preferences and choice. In addition, there are phenolic acids that are only found in a particular variety of olive oil obtained from fruits at a specific ripening stage. Consequently, phenolic acids could be used as potential markers for olive oil variety and harvest time.     

Endogenous microflora in turbid virgin olive oils and the physicochemical characteristics of these oils

Cloudy olive oil, the fresh olive juice, is an intermediate form before full precipitation of freshly produced olive oil. Some consumers prefer it because they consider it as more natural and less processed. The cloudy form can persist for several months. The oil is a sort of dispersion/suspension system which can be also described as a micro‐emulsion/suspension. Water micro‐droplets were found to have a size ranging from 1 to 5 µm. Cloudiness is due to the low water content and the presence of natural emulsifiers in the oil. The suspension is formed by solid particles (5–60 µm) deriving from the olive fruit. They are present in small amounts (12–460 mg/kg oil). In the newly produced olive oil, containing 0.17–0.49% water, a number of microorganisms of different types (bacteria, yeasts, moulds) were found to survive, but at very low concentrations (<3 log cfu/mL oil). They originate from the exterior of the fruit (epiphytic microflora) and their presence is considered natural. Their enzyme activities do not seem to affect the quality of the final product.     

The contents of proteins and phospholipids in cloudy (veiled) virgin olive oils

Extra virgin olive oil is produced in the form of a “suspension–dispersion” which can persist for several months before full deposition of a residue. Many consumers and chefs prefer unfiltered raw olive oil because it looks thicker and richer in flavors. The nature of the material in the suspension–dispersion is poorly described. The presence of proteins has been connected with the appearance of the “veiled” oil and also with its oxidative stability, although there are discrepancies in the literature with regard to their levels. The level of phosphorus, a measure of phospholipids, is also poorly studied. This work aims at quantifying proteins and phospholipids in cloudy olive oil. For the analysis of proteins, a practical method is used that can be applied for routine analysis. The proteins are precipitated with acetone and determined colorimetrically using the Bradford method suitably modified to measure protein dye‐binding at low concentrations. Twenty three virgin and one refined olive oil samples from different places in Greece were all found to have protein levels below 2.5 mg/kg. In most of the samples, values were lower after filtration of the cloudy oils. In the refined oil samples, protein was hardly determined (value ≤0.1 mg/kg). Phosphorus levels ranged from 0.8 to 4.8 mg/kg. These correspond to approximately 21–124 mg/kg of phospholipids. The results are discussed in relation to the oxidative and physicochemical stability of the veiled oils.     

Characteristics of tea seed oil in comparison with sunflower and olive oils and its effect as a natural antioxidant

A comparison of iodine values showed that the degree of saturation of tea seed oil (Lahjan variety) was intermediate between the oils of sunflowerseed (Fars variety) and olive (Gilezeytoon variety), and the saponification values of these three oils were similar. Tea seed oil consisted of 56% oleic acid (C18∶1), 22% linoleic acid (C18∶2), 0.3% linolenic acid (C18∶3), and therefore, on the basis of oleic acid, occupied a place between sunflower and olive oil. In studies at 63°C, the shelf life of tea seed oil was higher than that of sunflower oil and similar to olive oil. Tea seed oil was found to have a natural antioxidant effect, and it enhanced the shelf life of sunflower oil at a 5% level. In this study, tea seed oil was found to be a stable oil, to have suitable nutritional properties (high-oleic, medium-linoleic, and lowlinolenic acid contents), and to be useful in human foods.     

Separation of wax esters from olive oils by high-performance liquid chromatography

To detect adulteration of olive oil with solvent-extracted oils, the determination of the wax ester content has become more important during recent years. Hence, a greater number of wax ester analyses need to be performed by quality control laboratories. The most common method in use requires a liquid chromatographic (LC) separation of the less polar fraction, which contains the wax esters, from the glyceride matter on a hand-filled silica gel column. The aim of this project was to verify the possibility of replacing LC with high-performance liquid chromatography by taking advantage of the greater reliability and repeatability of this technique, as well as of the possibility of making the separation automatic. The paper describes how to perform the analysis and the statistical test that was carried out; furthermore, a comparison has been made with the usual method and results are in good agreement.     

Chemometric criteria for the characterisation of Italian Protected Denomination of Origin (DOP) olive oils from their metabolic profiles

This study was conducted and carried out as a consequence of the European directives n°2081/92 and n°2037/93 in which regulations for the protection of denomination of origin of food commodities were established. The research work was intended to investigate if monovarietal oils may be differentiated by their basic chemical composition. A positive outcome of this pilot study would hopefully permit extension to the characterisation of Italian DOP (Protected Denomination of Origin) olive oils. In the olive, long‐chain alcohols, triterpenes and fatty acids, formed in distinct biosynthetic compartments, provide characteristic compositional data of an olive cultivar. The three classes of compounds were qualitatively and quantitatively determined by GC in six Italian olive cultivars, Coratina and Provenzale from Puglia, Frantoio and Moraiolo from Toscana, Bosana from Sardegna and Dritta from Abruzzo. Basic statistics and multivariate methods were first applied to the GC data of each class of compounds and then to the complete set of data with the aim of obtaining a clear discrimination of the cultivars. When Principal Components Analysis (PCA) was applied to the whole set of data consisting of alcohols, triterpenes and acids, the PCA revealed that the compounds (variables) that gave the better class distinction were: cycloartenol for Coratina, acids C20:0, C17:0, C18:0 for Dritta, citrostadienol for Frantoio and β‐sitosterol for Moraiolo. Bosana and Provenzale correlated with erythrodiol and uvaol. A correct assignment of each oil sample to its monovarietal group was obtained.     

A laboratory study of the bleaching process in stigmasta-3,5-diene concentration in olive oils

The bleaching effect was simulated in pilot plant by measuring the influence of temperature (40, 50, 60, 70, 80, and 90°C), time (5, 10, 15, 20, 25, and 30 min), and concentration of solid adsorbent [1.5 and 8% (w/w) of Tonsil supreme NFF] on stigmasta-3,5-diene (STIG) obtained by dehydration of steroidal compounds. Conditions were chosen to simulate those used in industrial operations. The presence of refined oils in extra virgin olive oil can be detected by these newly formed steroid hydrocarbons. Experimental results indicated that STIG did not exceed an imposed limit of 0.15 mg/kg in extra virgin olive oil, when oils were bleached with 1.5% earth at temperatures ≤80°C for 30 min in admixed to oils sold as virgin. A large proportion of the adulterations were not detectable by the official methods. Color determinations (CIE-1931) chromatic coordinates) were replicated on a refined oil and in admixed extra virgin olive oil. Color of olive oil was not significantly affected by mixing with refined oil (≤20%).     

Fatty acid esters with short‐chain alcohols in two‐phase olive pomace oils

Two‐phase decanter olive pomace (TPOP) is the by‐product of a centrifugation system, used to produce olive oil, that separates olive oil and moist pomace. The water content in these olive pomaces is about 70%, while it was 45‐50% in the olive pomace stemming from three‐phase systems (oil, water, and pomace) and 30% in the old press system. The aim of this work is focused on quantification and changes undergone during olive pomace storage in ponds of esters of fatty acids with short‐chain linear alcohols, which can be considered as a refining loss. The results indicate that oil deterioration increases very rapidly, in particular when oil is extracted from the TPOP surface. Special attention should be paid to the storage of TPOP, establishing a maximum of 2 months in all cases.     

Predicting temperature-dependence viscosity of vegetable oils from fatty acid composition

The viscosities of 12 vegetable oils were experimentally determined as a function of temperature (5 to 95°C) by means of a temperature-controlled rheometer. Viscosities of the oil samples decreased exponentially with temperature. Of the three models [modified Williams-Landel-Ferry (WLF), power law and Arrhenius] that were used to describe the effects of temperature on viscosity, the modified WLF model gave the best fit. The amounts of monounsaturated FA or polyunsaturated fatty acids (PUFA) highly correlated (R ²>0.82) with the viscosities of the oil samples whereas and the amounts of saturated or unsaturated FA. An exponential equation was therefore used to relate the viscosity of these vegetable oil samples to the amounts of monounsaturated FA or PUFA. The models developed are valuable for designing or evaluating systems and equipment that are involved in the storage, handling, and processing of vegetable oils.     

从中药材女贞子中提取药效成分齐墩果酸最佳工艺研究

本文研究了从女贞子中提取药效成分齐墩果酸的最佳工艺。利用超声波破碎法使皮仁分离并提取、经酸沉碱溶盐析、酸处理脱色脱脂、纯化结晶等步骤研究提取工艺条件。结果表明,从女贞子中提取齐墩果酸的最佳条件为：液固比为20∶1;超声波的功率为200W;提取温度为60℃;乙醇体积分数为70%;提取时间为50min,提取率为92%。结论该工艺简便易行、提取率高、能耗小、溶剂损失小,有推广应用价值。     

Effects of neutralization with lime on the quality of acid olive oil

The technique described in this study makes it possible to neutralize olive oils having very high acidities. The neutralization is carried out in a solid-liquid biphasic medium, which is slightly hydrated, by substituting lime (calcium hydroxide, an inexpensive and locally manufactured product) for soda (sodium hydroxide) as the neutralizing agent. Neutralization by lime limits TAG hydrolysis. The use of lime as a neutralizing agent makes it possible to preserve almost 80% of the α-tocopherol. Oils neutralized with lime have higher temperatures of thermal decomposition than oils neutralized with soda. Oils neutralized with lime had better oxidative stability because natural antioxidants were preserved. Oils neutralized by lime conformed with international olive oil standards.     

Phenolic composition of virgin olive oils from cross breeding segregating populations

The evaluation and characterization of segregating populations is a critical step in olive breeding programs. In this work, phenolic profiles of virgin olive oils (VOOs) from segregating populations obtained by cross breeding in Cordoba (Spain) have been evaluated. Genotypes obtained from open pollination of the cultivar Manzanilla de Sevilla, and from crosses between the cultivars Arbequina × Arbosana, Picual × Koroneiki and Sikitita × Arbosana were tested. The phenolic composition was determined after liquid–liquid extraction with 60:40 v/v methanol–water and subsequent chromatographic analysis with ultraviolet (UV) detection of both absorption and fluorescence in a sequential configuration. Results for all studied compounds showed high degree of variability between genotypes, with a higher range of variation than the observed for the genitors. Most of the observed variability was attributable to differences in genotypes within crosses rather than among crosses. Some issues related to breeding strategies are discussed. Practical applications: Phenolic compounds are considered to be of paramount importance for the assessment of virgin olive oil quality due to their contribution to the nutraceutical and sensory profile of this natural food. This study focuses on the evaluation of the content of phenolic compounds in olive oils originated from cross breeding in an olive breeding program (Cordoba, Spain). This step is crucial to determine the range of variation of phenolic compounds and the selection of interesting genotypes with higher composition in total phenols or in an individual phenol targeted at a breeding program.     

Antioxidant capacity of extra-virgin olive oils

In this study, the oxygen radical absorbance capacity (ORAC) of vegetable oils was investigated using a spectrofluorometric method, which measures the protection of the phenolic substances of the oil on the β-phycoerythrin fluorescence decay in comparison with Trolox. More than 97% of the phenolic substances was extracted from the oil using methanol, and the methanolic extract was then used for the ORAC and the total phenolics assay. We found a significant correlation between ORAC values of different olive oils and the total amount of phenolics. For extra-virgin olive oils, maximal ORAC values reached 6.20±0.31 μmol Trolox equivalent/g, while refined and seed oils showed values in the 1–1.5 μmol Trolox equivalent/g range. Our method is useful to assess the quality of olive oils and to predict, in combination with the rancidity tests, their stability against oxidation.     

Study of the enantiomeric composition of chiral constituents in edible oils by simultaneous distillation-extraction. Detection of adulterated olive oils

A method is proposed for detecting adulterations of olive oil with hazelnut oil at percentages as low as 5%. The method is based on the identification of R- and S-enantiomers of E-5-methylhept-2-en-4-one (filbertone) and involves the use of simultaneous distillation-solvent extraction in the sample preparation step and subsequent gas chromatographic analysis with a chiral stationary phase. Relative standard deviation values obtained from three replicates of adulterated mixtures of olive oil and hazelnut oil (95:5) were less than 9% for both R-and S-filbertone.     

Evaluation of olive oils through the fatty alcohols,the sterols and their esters by coupled LC-GC

The analysis of the fatty alcohols, the wax esters, the free and the esterified sterols, as well as that of minor components provides a wealth of information about the quality of an oil or fat, its pretreatment and admixture with other oils. Some results obtained by an easy, nearly fully-automated method are shown for olive oils. More specific information is obtained than by the previous saponification methods.     

Classification of virgin olive oils of the two major cretan cultivars based on their fatty acid composition

Fatty acid composition was determined for 105 virgin olive oil samples of the two dominant Cretan olive cultivars, Koroneiki and Mastoides, harvested from different producing areas at different maturity stages. The oils of the Koroneiki cultivar were characterized by lower concentrations of oleic and decaheptanoic and higher concentrations of linoleic and palmitic acids. Oils obtained from high-altitude locations were rich in monounsaturated fatty acids, while oils obtained from low-altitude locations had higher content of saturated fatty acids. Palmitic and palmitoleic acids increased with increasing altitude in both cultivars examined. The statistical analysis of the compositional data showed significant potential for the classification of the samples according to cultivar and location of origin.     

High-performance liquid chromatography of selected phenolic compounds in olive oils

A reverse-phase high-performance liquid chromatographic technique with isocratic elution has been developed to separate and quantitate the major phenolic compounds of the hydroalcoholic extracts of olive oils. Hydroxytyrosol, tyrosol, caffeic acid,p-hydroxyphenylacetic acid and homovanillic acid were analyzed on a μBonapak C18 column with an acetonitrile/water/acetic acid (20:90:0.18, vol/vol/vol) mixture as a mobile phase. Electrochemical detection provided selectivity as well as sensitivity. The method was applied to the analysis of the most important phenolic compounds in olive oils.