Aroma biogenesis and distribution between olive pulps and seeds with identification of aroma trends among cultivars

The two constitutive parts of four cultivars (Arbequina, Picual, Local and Manzanilla de Sevilla) grown in Spain were separately analysed in order to establish the role of pulp and seed in the biogenesis of extra virgin olive oil (EVOO) aroma through the lipoxygenase (LOX) pathway. C6 and C5 volatile compounds responsible of EVOO aroma were produced by endogenous enzymes in both parts of olive fruits and the differences can be attributed to different enzymes distribution in pulp and seed. According to results, C6 and C5 volatile compounds have mainly their biogenesis in pulp (80–90%) vs. seed (20–10%), independently of the cultivar considered. A linear discriminant analysis was used to establish discriminant aroma compounds between pulp and seed related to the maturity index. A decrease in trans-2-hexen-1-al and an increase in 1-hexanol with ripeness were observed independently of the cultivar considered. Finally, Partial Least Squares (PLS) regression analysis between pulp and seed aroma compounds allowed to establish those volatile compounds that better describe each cultivar.     

Predicting the end point of a blanching process

Thermal inactivation of peroxidase and lipoxygenase during blanching of a solid food with a finite cylinder shape (diameter=9 cm and heitght=20 cm) has been mathematically studied in order to evaluate the end point of the process. Predictions included thermal inactivation of peroxidase and lipoxygenase during heating in steam of a conventional blanching process, and thermal inactivation of lipoxygenase during an individual and quick blanching process. It was assumed an inactivation biphasic model to describe the inactivation first-order thermal kinetics of peroxidase and lipoxygenase. Heat transfer conditions, the total initial indicator enzyme activity, the proportion of resistant and labile isoenzymes, kinetic parameters and the end point that the analytical method to be used may detect are important factors to predict and optimize a blanching process. For the conditions evaluated the worst scenario was a total initial peroxidase or lipoxygenase activity of 500 UA/g, 10% of resistant isoenzyme, being 1060 and 180 s, respectively, the heating times necessary to reach an end point of 1 UA/g. Heating times can be significantly reduced if an individual quick blanching process is used.     

Improvement of oleuropein extractability by optimising steam blanching process as pre-treatment of olive leaf extraction via response surface methodology

Impact of steam, hot water blanching and UV-C irradiation as pre-treatments on extraction of oleuropein and related biophenols from olive leaves (OLs), was investigated. Moreover, particle size effect of olive leaves and steam blanching duration were selected as independent variables to optimise steam blanching process in terms of oleuropein content (OC) and antioxidant activity (AC) of ethanolic extracts, by using response surface methodology. Optimum conditions for OC and AC were 10 min steam blanching of 20–11 and 3–1 mm olive leaf fraction, respectively. Depending on the extraction procedure, at optimum conditions of steaming the results indicate that steam blanching of OL prior to extraction can significantly increase oleuropein yield from 25 to 35 times compared to non-steam blanched sample, whereas the antioxidant activity increased from 4 to 13 times. No significant UV-C effect was observed in OC and AC, while hot water blanched samples showed significantly higher oleuropein yields and antioxidant activity compared to untreated samples.     

Effect of storage temperatures on antioxidant capacity and aroma compounds in strawberry fruit

The antioxidant capacity (measured as oxygen radical absorbance capacity, ORAC), total anthocyanins, total phenolics, aroma compounds, and postharvest quality of strawberry fruit (Fragaria x ananassa cv. Chandler) kept at 0°C, 5°C, and 10°C were investigated. Strawberry fruit stored at 10°C or 5°C showed higher antioxidant capacity, total phenolics, and anthocyanins than those stored at 0°C. However, the postharvest life based on overall quality was longer at 0°C than at 5°C or 10°C. The production of aroma compounds was markedly influenced by storage time and temperature. Individual aroma compounds were affected differently. For example, ethyl hexanoate, hexyl acetate, methyl acetate, and butyl acetate increased, while 3-hexenyl acetate and methyl hexanoate decreased during storage. In general, strawberries stored at 10°C or 5°C produced higher levels of these volatiles than those stored at 0°C. In conclusion, strawberries stored at 0°C retained an acceptable overall quality for the longest storage duration; however, berries stored at temperatures higher than 0°C showed higher content of aroma compounds and antioxidant capacity during the postharvest period.     

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.     

Oxidative stability of olive oil and its polyphenolic compounds after boiling vegetable process

The changes in the stability and phenolic content of an extra-virgin olive oil and an olive oil following boiling operation in the presence of vegetables have been studied. After the boiling process, none of the olive oil samples was oxidized, independently of the olive oil quality used. However, in contrast with tocopherols, all polyphenolic components decreased in concentration with the thermal treatment and this decrease was dramatic in the presence of vegetables, probably because of their high content in metals such as iron and copper. The addition of olive oil only 15 min before the end of the boiling process was shown to bring benefits in general for the content of both elenolic acid derivatives, 3,4-DHPEA-EA and 4-HPEA-EA, and hydroxytyrosol acetate in the processed oils. Moreover, less destruction of the vegetables polyphenols was also observed when processing olive oils only 15 min before the end of the boiling process. Interestingly, and besides the use of EVOO instead of OO did not bring benefits to the stability of samples or a higher polyphenolic content in the samples after processing, an higher radical scavenging capacity of phenolic extracts obtained from EVOO samples could be observed.     

橄榄油在高温条件下的稳定性研究

对橄榄油进行煎炸和加热试验,考察高温下橄榄油的稳定性。通过取样检测发现,煎炸橄榄油15 min或加热橄榄油3 min内,橄榄油的酸价、过氧化值和角鲨烯含量的变化较小,性质较为稳定,由此可见,橄榄油可适用于短时间烹调。     

Looking through the qualities of a fluorimetric assay for the total phenol content estimation in virgin olive oil,olive fruit or leaf polar extract

As an alternate to the Folin-Ciocalteu assay (F-C) we propose a fluorimetric estimation of the total phenol content in virgin olive oil (VOO), olive fruit and leaf polar extracts. Phenol content was determined at excitation/emission wavelengths set at 280/320 nm. Standard operational procedures (slit widths, temperature, pH) and method validation were carried out according to Eurachem guidelines. The qualities of the proposed assay are better than those of the F-C one, as the procedure is more sensitive (LOD and LOQ values 10-fold lower), three times faster, needs no reagents and most importantly, is not destructive for the sample that can be further used in HPLC or other assays. Data for VOO extracts correlated well with the colorimetric ones (r = 0.69, n = 65). HPLC coupled with diode array and fluorescence detectors supported the above findings. Good correlations were also found between the respective data for olive fruit and leaf extracts (r = 0.96, n = 18).     

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.     

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.     

The detection of the presence of hazelnut oil in olive oil by free and esterified sterols

Genuine olive and hazelnut oils from diverse geographical origins, as single varieties and blends, were mixed at different percentages and analysed by the method based on the quantification of free and esterified sterols. Two formulas based on three sterols (Campesterol, Δ⁷-stigmastenol and Δ⁷-avenasterol) together with empirical decision rules were able to detect the presence of hazelnut oil in olive oil when the percentage of the former was more than 6–8%, although this figure was much lower in the most of the adulterations. Results of univariate and multivariate statistical procedures based on the analysis of 116 samples are presented in support of the method efficiency.     

Effect of repeated frying on the viscosity, density and dynamic interfacial tension of palm and olive oil

The effect of deep-fat frying on the viscosity, density and dynamic interfacial tension (against air and water) of palm oil and olive oil was investigated. Repeated frying (up to 40 batches) at two different potato-to-oil ratios (1/7, 1/35 kg_potatoes/L_oil) was examined. Results were compared to those from simple heating the oils at the same temperatures. Viscosity increased during repeated frying for both oils. However, only palm oil viscosity was sensitive to potato-to-oil ratio. Due to the novelty of dynamic interfacial characterization of such systems a discussion was made about the appropriate timescales and deformation types for interfacial measurements. Significant effects of repeated frying on the dynamic interfacial tension at the oil/water interface were observed. Contrarily, changes in density were not significant. Results were assessed with respect to the evolving chemical profile of the oils determined in previous works. Possible implications of the determined properties on the frying process were discussed.     

Detection of olive oil using the Evagreen real-time PCR method

A sensitive real-time PCR method using the novel fluorescence stain Evagreen was established for detection of olive oil. First, a comparative study was made of two different methods for the recovery of high quality DNA from oil samples. Thereby, the Promega wizard DPSF kit proved to be the most suitable for recovery of DNA from oil samples. Second, an olive-specific pair of primers was designed based on the sequence of an olive plasma intrinsic protein cDNA sequence. Experiments with 13 samples including olive, soybean, sesame, sunflower seed, pumpkinseed, walnut, rapeseed, rice, peanut, maize, pig, chicken and fish confirmed that this pair of primers is highly specific for olive. Additional experiments indicated that the absolute detection limit of our test is 0.07 ng olive DNA and that 0.5% olive DNA can be detected against background of 2 ng/μl sesame DNA.     

浙江山核桃油脂香气萃取条件优化及组分分析

采用HS-SPME-GC-MS方法对浙江山核桃香气成分进行定性定量分析.通过单因素试验和正交试验,优化固相微萃取的条件,建立山核桃油脂香气组分分析的方法.结果表明:采用50 μm/30 mm DVB/CAR-PDMS萃取头,加入2 g 样品量,在50 ℃条件下萃取40 min,GC-MS色谱图峰面积最大;经HS-SPME-GC-MS分析,从浙江山核桃油中共检测出香气成分42种,主要包括醛类、醇类、烯类、酯类、酮类以及其他一些化合物.     

Microwave heating of different commercial categories of olive oil: Part II. Effect on thermal properties

The effect of microwave heating of commercial categories of olive oil for human consumption (extra virgin olive oil [EVOo], olive–pomace oil [Po] and olive oil [Oo]) on DSC thermal properties was evaluated at different times of microwave treatment.     

Coupling MOS sensors and gas chromatography to interpret the sensor responses to complex food aroma: Application to virgin olive oil

This paper describes a novel approach to determine the individual contribution of volatile compounds to the overall sensor responses of metal oxide semiconductor (MOS) sensors when they are applied to a complex mixture of compounds such as food aroma. A methodology entailing the use of a sensor array or electronic nose (EN) as non-destructive detector in-parallel with the flame ionization detector of a gas chromatograph (GC) is described and illustrated in the context of virgin olive oil aroma analysis. Aspects related to the experimental set up and data processing are examined. The capability of gas chromatography for obtaining qualitative and quantitative information of the volatile compounds present in virgin olive oil was used to find relationships between these compounds and the sensor responses by means of a coupled system GC–EN. The sensor responses that resulted from this coupling (sensorgrams) served to prove the sensor sensitivity to alcohols, aldehydes, and those compounds that are responsible to sensory defects in virgin olive oil (e.g. aldehydes and acids).     

Impact of olive oil phenolic concentration on human plasmatic phenolic metabolites

Three different functional phenol-enriched virgin olive oils (FVOO) were prepared with a phenolic content of 250 (L-FVOO), 500 (M-FVOO), and 750 mg (H-FVOO) total phenols/kg. In a randomised, cross-over study with 12 healthy volunteers, the pharmacokinetics of phenolic biological metabolites was assessed. An increasing linear trend was observed for hydroxytyrosol sulfate, the main phenolic metabolite quantified in plasma, with C_max values of 1.35, 3.32, and 4.09 μmol/l, and AUC mean values of 263.7, 581.4, and 724.4 μmol/min for L-FVOO, M-FVOO, and H-FVOO, respectively. From our data an acute intake of phenol-enriched olive oils promotes a dose-dependent response of phenol conjugate metabolites in human plasma. Also, we point out for the first time hydroxytyrosol acetate sulfate as a main biological metabolite of hydroxytyrosol from olive oil ingestion.     

Application of real-time PCR on the development of molecular markers and to evaluate critical aspects for olive oil authentication

Olive oil authentication using DNA-based markers is becoming very important. qRT-PCR was an efficient tool in investigating the utility of PCR primers for olive oil authentication allowing to discard primers with low PCR efficiency. It also allows investigating of the relative effectiveness among four DNA isolation methods and therefore qRT-PCR would be useful for further optimisation of the DNA extraction protocols. The number of target molecules for the amplification of 80 bp amplicons was higher than that of 200 bp. Therefore the amplicon size should be optimised for olive oil authentication since the higher the number of templates the greater the probability of successful amplification. On conclusion, qRT-PCR is a useful tool in the development of molecular markers for olive oil authentication and it should be used for the optimisation of critical parameters such as the amplicon size and the DNA extraction method.     

Biosensors for monitoring the isothermal breakdown kinetics of peanut oil heated at 180 °C. Comparison with results obtained for extra virgin olive oil

The present research was devoted to studying the kinetics of the artificial rancidification of peanut oil (PO) when a sample of this oil was isothermally heated at 180 °C in an air stream. The formation of radical species due to heating was evaluated using a radical index whose value was determined using a biosensor method based on a superoxide dismutase (SOD), while the increasing toxicity was monitored using a suitable toxicity measuring probe based on the Clark electrode and immobilized yeast cells.