Comparative trials and an empirical model to assess throughput indices in olive oil extraction by decanter centrifuge

Interesting performance indices for a decanter centrifuge used in oil extraction from olive paste were found through an empirical black box approach to oil extraction using a decanter centrifuge validated with experimental data. The performance indices identified were: oil recovery efficiency, the separation coefficient and husk water content.     

Salt improves physical extraction of olive oil

The use of two concentrations of common salt (0.6 and 1.2%) as coadjuvant for the physical extraction of olive oil has been tested at a laboratory scale and compared with those tests which did not use a coadjuvant or used talc, the only coadjuvant that is allowed according to EC regulations, using the fruits of six different olive varieties (Olea europaea L. cvs. Arbequina, Hojiblanca, Lechín, Manzanilla, Picual, and Verdial). Common salt systematically allowed a higher oil yield than the controlled extraction without coadjuvants, with similar recovery rates to those values obtained when using the more expensive alternative of talc. Physico-chemical quality parameters of the virgin olive oils were not significantly affected by the use of this coadjuvant. However, the levels of oil stability, pigment content or intensity of bitterness were slightly increased. Salt addition seems to be a feasible alternative for the improvement of oil extraction. No appreciable advantages were observed when using the higher concentration of salt tested.     

Horizontal centrifuge with screw conveyor (decanter): Optimization of oil/water levels and differential speed during olive oil extraction

Olive oil extraction using a horizontal centrifuge with a screw conveyor is an essential operation to reduce production costs. However, proper control of the plant is required to maintain a high level of extraction yield and olive oil quality. Rheological characteristics of the olive paste, which change in relation to water content, fruit variety, maturity level and seasonal temperature variations, greatly affect the efficiency of centrifugal extraction. If olive paste is fed to a decanter without automatic control, then non-optimal extraction is performed.     

Acephate and buprofezin residues in olives and olive oil

Field trials were carried out to study the persistence of acephate and buprofezin on olives. Two cultivars, pizz'e carroga and pendolino, with very large and small fruits respectively were used. After treatment, no difference was found between the two pesticide deposits on the olives. The disappearance rates, calculated as pseudo first order kinetics, were similar for both pesticides (on average 12 days). Methamidophos, the acephate metabolite, was always present on all olives, and in some pendolino samples it showed higher residues than the maximum residue limit (MRL). During washing, the first step of olive processing, the residue level of both pesticides on the olives did not decrease. After processing of the olives into oil, no residues of acephate or methamidophos were found in the olive oil, while the residues of buprofezin were on average four times higher than on olives.     

Estimation of olive oil acidity using FT-IR and partial least squares regression

Olive oil characteristics are directly related to olive quality. Information about olive quality is of paramount importance to olive and olive oil producers, in order to establish its price. Real-time characterization of the olives avoids mixtures of high quality with low quality fruits, and allows improvement of olive oil quality. This work describes an indirect determination of olive acidity and that allows a rapid evaluation of olive oil quality. The applied method combines chemical analysis (30 min Soxhlet olive pomace extraction) in tandem with a spectroscopic technique (FT-IR) and multivariate regression (PLS1). The most suitable calibration model found used SNV pre-processing and was built with 4 Latent Variables giving a RMSECV of 8.7% and a Q² of 0.97. This accurate calibration model allows the estimation of olive acidity using a FT-IR spectrum of the corresponding Soxhlet oil dry extract and therefore is a suitable method for indirect determination of FFA in olives.     

High throughput flow injection bioluminometric method for olive oil antioxidant capacity

This paper describes a rapid flow injection automated method for the determination of olive oil total antioxidant capacity. The chemistry involved is the horseradish peroxidase (HRP) catalysed oxidation of luminol by hydrogen peroxide. Oxidation results in light emission (bioluminescence) that is enhanced using p-iodophenol sensitizer. Olive oil (0.7 mL) is extracted with two 0.7 mL aliquots of 80–20% (v/v) methanol–water solvent. A 17 μL aliquot of the extract containing hydrophilic antioxidants is injected in a phosphate buffer channel that subsequently merges with a luminol–HRP–p-iodophenol reagent stream. Bioluminescence resulting after merging the mixture with a hydrogen peroxide stream is suppressed upon increasing antioxidants’ concentration resulting in negative peaks due to hydrogen peroxide consumption by antioxidants. The method has been optimized on (a) number of manifold channels, (b) flow rates, (c) coil length and (d) HRP, hydrogen peroxide and p-iodophenol concentrations. Detection limit is calculated at 1.5 × 10⁻⁷ M gallic acid, linear range is between 1.0 × 10⁻⁶ and 1 × 10⁻⁴ M and precision is better than 2.8% RSD (n = 4). The fully automated method is achieving a rate of sampling equal 180 probes per hour. The proposed method is applied for the assessment of 50 extra-virgin olive oil samples of different Greek cultivars and regions.     

Composition of total sterols (4-desmethyl-sterols) in extravirgin olive oils obtained with different extraction technologies and their influence on the oil oxidative stability

The composition and antioxidant activity of total sterols in extravirgin olive oils obtained with different extraction technologies from olives harvested at two ripening stages, were studied. The antioxidant activity was evaluated with an oxidative stability instrument (OSI), by using a model system (made of a mixture of treated/untreated commercial refined peanut oil) enriched with the total sterol fractions of the extravirgin olive oils. No correlation was found between the OSI time and the extraction technologies, the ripening stages or the actual amount of sterols added. No significant differences were observed in the percent composition of sterols of extravirgin olive oils produced with different technologies during the same harvesting period. The latter, however, had a significant effect on the percent of β-sitosterol and 5-avenasterol in extravirgin olive oils produced with the same technology.     

Comparative study of different extraction techniques for the analysis of virgin olive oil aroma

Headspace solid-phase microextraction (HS-SPME), simultaneous distillation/extraction (SDE) and closed-loop stripping analysis (CLSA) coupled to gas chromatography/mass spectrometry (GC/MS) were used to study virgin olive oil, with the goal of detecting large numbers of characteristic volatile and semi-volatile compounds. More than one hundred compounds were detected in the olive oil extracts, and their percent amounts obtained by each technique were calculated. Qualitative and quantitative differences of virgin olive oil volatile profiles were observed applying the three extraction techniques. SPME showed a higher affinity for alcohols and ketones, while CLSA achieved the highest percentages of esters and hydrocarbons. Finally, the highest extraction of total terpenoid compounds occurred with SDE and CLSA, where CLSA allowed extracting the highest percentages of the most of them. SDE extraction caused the thermal degradation of the oil sample, which resulted in a high percentage of aldehydic compounds.     

Distribution of dimorphic yeast species in commercial extra virgin olive oil

Recent microbiological research has demonstrated the presence of a rich microflora mainly composed of yeasts in the suspended fraction of freshly produced olive oil. Some of the yeasts are considered useful as they improve the organoleptic characteristics of the oil during preservation, whereas others are considered harmful as they can damage the quality of the oil through the hydrolysis of the triglycerides. However, some dimorphic species can also be found among the unwanted yeasts present in the oil, considered to be opportunistic pathogens to man as they have often been isolated from immunocompromised hospital patients. Present research demonstrates the presence of dimorphic yeast forms in 26% of the commercial extra virgin olive oil originating from different geographical areas, where the dimorphic yeasts are represented by 3–99.5% of the total yeasts. The classified isolates belonged to the opportunistic pathogen species Candida parapsilosis and Candida guilliermondii, while among the dimorphic yeasts considered not pathogenic to man, the Candida diddensiae species was highlighted for the first time in olive oil. The majority of the studied yeast strains resulted lipase positive, and can consequently negatively influence the oil quality through the hydrolysis of the triglycerides. Furthermore, all the strains showed a high level of affinity with some organic solvents and a differing production of biofilm in “vitro” corresponded to a greater or lesser hydrophobia of their cells. Laboratory trials indicated that the dimorphic yeasts studied are sensitive towards some components of the oil among which oleic acid, linoleic acid and triolein, whereas a less inhibiting effect was observed with tricaprilin or when the total polyphenols extracted from the oil were used. The observations carried out on a scanning electron microscope (SEM), demonstrated the production of long un-branched pseudohyphae in all the tested dimorphic yeasts when cultivated on nutrient-deficient substrates.     

溶剂浸取法提取麻疯果仁油的工艺研究

采用溶剂浸取法提取麻疯果仁油,考察了浸取温度、浸取次数、液料比、浸取时间等因素对提油效果的影响。实验得到的最佳逆流浸取工艺条件为:浸取温度60℃,浸取级数5级,液料比8∶1,单级浸取时间1 h。在该工艺条件下,麻疯果仁油的提取率可达99.1%,脱溶后所得毛油酸值(KOH)在2.8~4.2 mg/g之间,可直接用作制备生物柴油的原料油。     

南瓜籽油提取工艺优化及油脂氧化稳定性研究

以南瓜籽为原料,研究溶剂浸提法提取南瓜籽油最佳工艺。研究了温度、时间和料液比3个因素对提取率影响,并且通过正交试验对溶剂浸提法提取南瓜籽油工艺流程进行了优化。最佳提取条件:提取温度55℃,时间3 h,料液比1∶10时,提取率可达93.4%。     

酶的选择对水酶法提取核桃油的影响

研究了中性蛋白酶(PR)、中温淀粉酶(α-AM)、果胶酶(PE)和纤维素酶(CE)单独使用和两种复配使用、3种复配使用对总油和清油提取率的影响。结果显示,蛋白酶对清油提取率效果最好,纤维素酶作用次之;两种酶复配使用时,蛋白酶和纤维素酶复配清油提取率可达40%以上,淀粉酶与纤维素酶复配效果也较好;3种酶复配使用时,蛋白酶、纤维素酶与果胶酶的复配效果最好,淀粉酶、蛋白酶与纤维素酶的复配效果次之,但对清油提取率提高作用不大。     

Enzymatic hydrolysis and pressing conditions effect on borage oil extraction by cold pressing

Borage seed oil extraction using cold pressing produces a good oil quality, but it has a low-yield. In a previous study on a borage oil extraction process by cold pressing using commercial enzymes, the oil yield was enhanced in comparison to the control without enzymes. The aim of this work was to further evaluate the effect of temperature, moisture and time of enzymatic hydrolysis; and the effect of this treatment under selected conditions on the pressing stage and on product qualities. The best treatment condition with Olivex–Celluclast was 45 °C, 20% moisture over 9 h of treatment. When the extraction of the pre-treated borage meal was carried out by double pressing (20 min each) on preheated matter, 95% of the oil was recovered. The enzymatic treatment did not affect the oil quality and the residual meal was more valuable due to its lower fibre content.     

Phenolic and antioxidant potential of olive oil mill wastes

Olive oil mill waste was subjected to conventional liquid solvent extraction and supercritical fluid extraction using different solvents and carbon dioxide, respectively. The optimum solvent extraction conditions of phenols were 180 min using ethanol, at a solvent to sample ratio 5:1 v/w, and at pH 2. Solvent and SFE extracts were tested for their antioxidant activity by the DPPH radical scavenging method and by determination of peroxide value on virgin olive oil and sunflower oil. The ethanol extract exhibited the highest antiradical activity, and no correlation was found between antiradical activity and phenol content. The SFE extract exerted good antioxidant capacity although its phenolic yield was not quite high. Moreover, the ethanol extract appeared to be a stronger antioxidant than BHT, ascorbyl palmitate and vitamin E by the Rancimat method on sunflower oil. HPLC analysis of the extracts showed that the predominant phenolic compound was hydroxytyrosol. Various phenolic acids and flavonoids were also identified.     

Melatonin is a phytochemical in olive oil

Given the numerous observations regarding the positive effects of olive oil consumption and the presence of melatonin in edible plants, we addressed for the first time the question of melatonin determination in virgin olive oil. All the extra virgin olive oil registered designation of origins from Spain and commercial samples of refined olive and sunflower oil were used. Immunoprecipitation and ELISA were combined for melatonin determination. Melatonin is present in olive oil at higher levels in extra virgin olive oil than in refined olive or sunflower oil samples. We concluded that melatonin is part of the phytochemical profile of the olive oil. Particularly, extra virgin olive oil had almost double the melatonin contents of the other refined oils analysed. Thus, melatonin may account for the healthy effects of the Mediterranean diet in which olive oil is the main source of fat.     

Direct analysis of glucuronidated metabolites of main olive oil phenols in human urine after dietary consumption of virgin olive oil

In the present study we report on a UPLC-MRM validated method for the simultaneous direct analysis of main glucuronidated metabolites of olive oil phenols: tyrosol, hydroxytyrosol and its O-methyl metabolite homovanillyl alcohol in human urine after dietary olive oil ingestion. The developed method was linear within the concentration range 20–2000 ng/mL with adequate recovery of analytes (>86%). Intra- and inter-day precision and accuracy were according to standard requirements for method validation criteria. Using the developed method, urinary concentrations and excretion rates of glucuronides of olive oil phenols were successfully estimated in an intervention study with 11 healthy volunteers supplemented with a dietary dose of virgin olive oil (VOO) (50 mL). Therefore, about 13% of the consumed olive oil polyphenols were recovered in 24-h urine, where 75% of them were in the form of glucuronides (3′- and 4′-O-hydroxytyrosol glucuronides, 4′-O-glucuronides of tyrosol and homovanillyl alcohol) and 25% as free compounds.     

Expert system based on computer vision to estimate the content of impurities in olive oil samples

The determination of the content of impurities is a very frequent analysis performed on virgin olive oil samples, but the official method is quite work-intensive, and it would be convenient to have an alternative approximate method to evaluate the performance of the impurity removal process. In this work we develop a system based on computer vision and pattern recognition to classify the content of impurities of the olive oil samples in three sets, indicative of the goodness of the separation process of olive oil after its extraction from the paste. Starting from the histograms of the channels of the Red–Green–Blue (RGB), CIELAB and Hue-Saturation-Value (HSV) color spaces, we construct an initial input parameter vector and perform a feature extraction previous to the classification. Several linear and non-linear feature extraction techniques were evaluated, and the classifiers used were Support Vector Machines (SVMs) and Artificial Neural Networks (ANNs). The best classification rate achieved was 87.66%, obtained using Kernel Principal Components Analysis (KPCA) and a grade-3-polynomial kernel SVM. The best result using ANNs was 82.38%, yielded by the use of Principal Component Analysis (PCA) with the Perceptron.