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.     

Tocols in caneberry seed oils

The compositional analysis of tocols in oils extracted from Korean caneberry seeds was compared with commercial soybean, corn, olive, canola, perilla, and grape seed oils. The oils from caneberry seeds of six different species were extracted using either a chloroform–methanol–water system or hot hexane. Tocols from all of the oils were analysed using isocratic HPLC. The contents of total tocopherols in the caneberry seed oils were about 75–290 mg/100 g oil, whereas tocotrienols were not detected. γ-Tocopherol was the most abundant tocopherol (31.8–239 mg/100 g oil) in the caneberry seed oils, followed by α-tocopherol (7.6–58.2 mg/100 g oil). The contents of total tocols in soybean, corn, olive, canola, perilla, and grape seed oils were 99.9, 61.1, 28, 27, 45.4, and 52.2 mg/100 g oil, respectively. Total tocol content was higher in most of the caneberry seed oils including the refined ones than in the commercial vegetable oils.     

Thermal oxidative process in extra-virgin olive oils studied by FTIR,rheology and time-resolved luminescence

With the aim to characterise the antioxidant properties of different extra-virgin olive oils and to understand in more detail the mechanisms of oil degradation, we have made an experimental study on thermal induced oxidative processes of extra-virgin olive oils by using different techniques: Fourier Transform Infrared (FTIR) spectroscopy, rheology and time-resolved luminescence. The oxidation process was followed at three different heating temperatures (30, 60 and 90 °C) as a function of time up to 35 days. Thermal treatment induced changes in the FTIR spectra in the wavenumbers region 3100–3600 cm⁻¹: in particular, the absorption profiles show an initial formation of hydroperoxides and a subsequent increase of alcohols and secondary oxidation products. In agreement with the FTIR data, rheology measurements show that after thermal treatment all examined samples exhibit an increase in the viscosity values with respect to pristine ones, indicating that the heat treatment induces the formation of polar molecules with propensity to form hydrogen bonds, which has as a consequence a viscosity increase. Finally, a lifetime increase of luminescence of chlorophyll is observed in agreement with the viscosity rise. Indeed, the viscosity increase reduces the frequency of collisions between the chromophore and its environment, consequently lowering the non-radiative contribution to the luminescence decay.     

Determination of apolar and minor polar compounds and other chemical parameters for the discrimination of six different varieties of Tunisian extra-virgin olive oil cultivated in their traditional growing area

A study on the characterization of Tunisian extra-virgin olive oil varieties produced in their place of origin has been carried out. Due to the influence of the genotype and environmental, agronomic and technological factors on the chemical composition of olive oil and its quality, all the olives studied were collected on the same season, and the oil was obtained under the same processing technique. Several analyses were performed to characterize the different olive oils: free acidity, peroxide value, fatty acid composition, radical scavenging activity, Rancimat assay, pigments content and phenolic compounds by HPLC–MS. In order to evaluate all the results obtained (36 parameters for each variety), different statistical analyses were used to discriminate the extra-virgin olive oil varieties: one-way analysis of variance was performed to check significant differences among cultivars (p ≤ 0.05); PCA was applied to the data showing that variables such as oleic, linoleic, quinic and vanillic acids, apigenin, luteolin, taxifolin, oleuropein aglycon, pinoresinol acetate, elenolic acid and oxidative stability allowed discriminating among the different varieties of extra-virgin olive oil studied. Besides, LDA model was able to classify the samples depending on their geographical origin in Tunisia (North, Centre and South).     

Are virgin olive oils obtained below 27 °C better than those produced at higher temperatures?

Within the European Union, indications of ‘first cold pressing’ and ‘cold extraction’ can only be used for virgin olive oil (VOO) obtained below 27 °C from mechanical processing. Three different malaxing temperatures (25, 35 and 45 °C) are here evaluated for the quality of the VOO obtained in a continuous industrial plant. The oils were stored at room temperature in the dark for 12 months. Initially, oil obtained from a blend of Frantoio/Leccino cultivars (F/L) had higher acidity and peroxide levels and lower phenolic content than a Coratina cultivar (Cor). The oxidative stability of the oils positively correlated with malaxation temperature (F/L, R² = 0.818; Cor, R² = 0.987) as the phenolic content was directly proportional to the temperature (F/L, R² = 0.887; Cor, R² = 0.992). Only oils obtained at 45 °C were rejected because of ‘heated or burnt’ off-flavour. Decarboxymethylation of secoiridoids and further hydrolysis of phenolic esters occurred during storage. The oxidation products of derivatives of tyrosol and hydroxytyrosol were detected after nine months in both the F/L and Cor samples. Thus, VOO obtained at a processing temperature lower than 27 °C does not show higher chemical and sensory qualities than VOO obtained at 35 °C.     

Effect of storage on refined and husk olive oils composition: Stabilization by addition of natural antioxidants from Chemlali olive leaves

Two samples of refined olive and husk oils have been analysed in order to evaluate the influence of storage time on their quality. The following parameters were determined: peroxide values, absorption coefficients K270 and K232, Rancimat induction time, sterols and fatty acid contents. Six months storage at 50 °C in the dark revealed a loss in oil stability. This finding was reflected by the greater increase in peroxide value and a decrease of Rancimat induction time and sterol content. The enrichment of refined olive and husk oils with olive leaves and its hydrolysate extract resulted in an appreciable resistance to oxidative deterioration due to its phenolic antioxidants content. Oleuropein and hydroxytyrosol were the major compounds in Chemlali olive leaves extract and hydrolysate solution, respectively. The antiradical activity of leaves extract as well as its hydrolysate solution was evaluated and compared to that of the BHT. The antioxidant activity of the enriched refined olive and husk oils with leaves and hydrolysate extracts at 400 ppm showed that the latter had the highest protective effect against oil oxidation. Oils with added hydrolysate extract had the lower peroxide value and the higher stability measured with a Rancimat method. After six months of storage the induction time increased from 23.3 to 83.5 h for refined olive oil and from 16.6 to 49 h for husk oil. Furthermore, during oil storage, there was no significant variation in fatty acid composition. However, the total sterol concentration of the oils treated with hydrolysate extract increased. The results suggested that hydrolysate and leaves extracts are excellent antioxidants and can serve as substitutes for synthetic antioxidants.     

Influence of filtering of cold pressed berry seed oils on their antioxidant profile and quality characteristics

The quality, composition and colour of 11 oils from six different berries were evaluated before and after filtering of the cold-pressed oils. The filtering did not lead to significant compositional or quality differences, except a minor reduction in oxidative stability. Due to their high degree of unsaturation, the peroxide and p-anisidine values were high for all oils. However, the high level of tocopherols and tocotrienols appears to protect the oils during the oil stability test (significant correlation; r = 0.803; p = 0.003). Tocopherol contents between 138 mg/kg (kiwi seed oil, filtered) and 1639 mg/kg (blackberry seed oil, non-filtered) were found. Phenolic compounds, identified and quantified by HPLC, ranged from 90 mg/kg (blackberry seed oil, filtered) to 15,810 mg/kg (strawberry seed oil, filtered). No correlation was found between the quantified phenolic compounds and the oxidative stability of the oils, suggesting that in these oils the tocopherols were the main antioxidants protecting the lipids during storage.     

Fatty acid composition,oxidative stability,antioxidant and antiproliferative properties of selected cold-pressed grape seed oils and flours

Cold-pressed chardonnay, muscadine, ruby red, and concord grape seed oils and their defatted flours were studied for their fatty acid composition, oxidative stability and antioxidant and antiproliferative activities. The phenolic profiles of the seed flours were also measured. The most abundant fatty acid in the oils was linoleic acid, ranging from 66.0 g/100 g of total fatty acids in ruby red seed oil to 75.3 g/100 g of total fatty acids in concord seed oil. The oils were also high in oleic acid and low in saturated fat. Ruby red grape seed oil recorded the highest oxidative stability index of 40 h under the accelerated conditions. Total phenolic content (TPC) was up to 100 times lower in the oils than in the flours. Lutein, zeaxanthin, cryptoxanthin, β-carotene, and α-tocopherol levels were also measured. DPPH radical-scavenging capacity ranged from 0.07 to 2.22 mmol trolox equivalents (TE)/g of oil and 11.8 to 15.0 mmol TE/g of flour. Oxidative stability of menhaden fish oil containing extracts of the seed flours was extended by up to 137%. HPLC analysis was conducted to determine the levels of free soluble, soluble conjugated and insoluble bound phenolics in the seed flours. The phenolic compounds analyzed included catechin, epicatechin, epicatechin gallate, quercetin, gallic acid, and procyanidins B1 and B2. Antiproliferative activity was tested against HT-29 colon cancer cells. All of the seed flours and muscadine seed oil registered significant (P < 0.05) inhibition of cancer cell growth. The results from this study demonstrate the potential of developing value-added uses for these seed oils and flours as dietary sources of natural antioxidants and antiproliferative agents for optimal health.     

Phenolic characterization and geographical classification of commercial Arbequina extra-virgin olive oils produced in southern Catalonia

The aim of this work was to characterize Arbequina extra-virgin olive oils (EVOOs) from different locations in southern Catalonia (Spain) in terms of their phenolic profile, to show the classification of oil samples with respect to geographical area. The phenolic compounds present in 32 olive-oil samples were analyzed by a rapid and effective HPLC–ESI-TOF/MS method, and 18 phenolic compounds belonging to different phenolic types were identified. The results showed no qualitative differences in the phenolic fractions among EVOO from different geographical region. However, quantitative differences were observed in a wide number of phenolic compounds. In all olive-oil samples studied, secoiridoids were the most abundant, followed by lignans, phenolic alcohols, and flavonoids, respectively. Multivariate data were analysed by canonical discriminant analyses. Seventeen variables were used without a variable reduction step. Phenolic content of extra-virgin olive oils was found to depend highly on geographical area.     

Pan-frying of French fries in three different edible oils enriched with olive leaf extract: Oxidative stability and fate of microconstituents

Sunflower oil, olive oil, and refined palm oil were enriched with an extract - rich in polyphenols - obtained from olive tree (Olea europaea) leaves at levels of 120 and 240 mg total polyphenols per kg oil. Potatoes were pan-fried in both the enriched and the non-supplemented oils under domestic frying conditions. Total polyphenols were estimated by Folin-Ciocalteu and antioxidant capacity was assessed by the DPPH radical scavenging assay. Tocopherols' content was determined by HPLC analysis, phytosterols and squalene by GC, and oxidative stability by Rancimat. Supplemented frying oils had higher total polyphenols and tocopherols' content, oxidative stability, and antioxidant capacity, while phytosterols and squalene content were not affected by the supplementation. French fries prepared in supplemented oils had higher total polyphenols, tocopherols, phytosterols, and squalene content and exhibited higher antioxidant capacity than those fried in non-supplemented oils. By consuming French fries pan-fried in enriched oils, up to 1.4-, 2.2-, and 1.5-fold increase of tocopherols, phytosterols, and squalene intake could be achieved as compared to those prepared in the non-supplemented oils.     

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.     

High performance size-exclusion chromatography analysis of polar compounds applied to refined, mild deodorized, extra virgin olive oils and their blends: An approach to their differentiation

An investigation was carried out to evaluate the use of High Performance Size-Exclusion Chromatography (HPSEC) of polar compounds of refined, mild deodorized, extra virgin olive oils as well as of their blends, in attempting to reveal significant differences in the amounts of the substance classes constituting polar compounds among these oils. Two sets of blends were prepared by mixing an extra virgin olive oil with both refined and mild deodorized olive oils in increasing amounts. The obtained data highlighted that the triacylglycerol oligopolymers were absent or present in traces in the extra virgin olive oil, while their mean amount was equal to 0.04 g/100 g and 0.72 g/100 g in mild deodorized and refined olive oils, respectively. Oxidized triacylglycerols and diacylglycerols were more abundant in mild deodorized oil and refined oil than in extra virgin olive oil. The Factorial Discriminant Analysis of the data showed that the HPSEC analysis could reveal the presence of refined/mild deodorized oils in extra virgin olive oils. In particular, the classification functions obtained allowed designation of mixtures containing at least 30 g/100 g of mild deodorized oil and all those containing refined olive oil as deodorized oil, therefore as oils subjected to at least a mild refining treatment.     

Oxidative stability enhancement of broiler bird meats with α-lipoic acid and α-tocopherol acetate supplemented feed

Depression of meat quality is known to be caused by lipid peroxidation occurring in meat. Supplementation of antioxidants in feed decreases lipid peroxidation and improves the oxidative stability of meat after slaughtering. The present study demonstrated that meat obtained from broiler birds fed feed supplemented with α-tocopherol acetate (200 mg/kg feed) along with α-lipoic acid (25, 75, or 150 mg/kg feed) exhibited increased oxidative stability and reduced fat content. The total phenolic content and α-lipoic acid content increased in the meat as the concentration of α-lipoic acid supplementation increased. The protein content in the meat was not changed by the supplementation of α-lipoic acid and α-tocopherol acetate. The results of DPPH and TBA assays demonstrated that feed supplemented with α-lipoic acid and α-tocopherol acetate also enhanced the antioxidant activity of broiler meat. On the other hand, the meat from broiler birds fed feed supplemented with oxidised oil (4% in feed) reduced its oxidative stability.     

Metal oxide semiconductor sensors for monitoring of oxidative status evolution and sensory analysis of virgin olive oils with different phenolic content

An electronic nose based on an array of six metal oxide semiconductor sensors was used to monitor the oxidative status of virgin olive oils (VOO) during storage. VOO samples, with and without phenolic compounds, were stored at 60 °C for 7 weeks. Once a week, absorbance at 232 and 270 nm, oxidized stability index, electronic nose, and sensory analysis were evaluated. Linear discriminant analysis models were constructed in order to classify samples according to oxidative levels. Based on these models, VOO samples with and without phenolic compounds at different storage times, divided in eight categories, were correctly classified also achieving a good correlation for sensory analysis. The method is a fast and economical tool for on-line monitoring of VOO oxidation status.     

Effects of different levels of trans fatty acids and oxidised lipids in diet on cholesterol and cholesterol oxidation products formation in rabbit

The objective was to assess the effects of trans fatty acids and oxidised lipids, present in dietary fat by-products used in feeds, on cholesterol and oxycholesterols in meat, liver and plasma of rabbits. A palm fatty acid distillate, before and after hydrogenation (trans fatty acid trial), and a sunflower–olive oil blend (70/30, v/v), before and after use in a commercial frying process (oxidised lipid trial), were used in experimental feeds (at 3%, w/w). High trans fatty acid and oxidised lipid diets caused significantly higher cholesterol and oxycholesterol levels in all tissues of rabbit (0.01 < p ? 0.05). The content of oxycholesterols in rabbit meat, liver and plasma obtained from trans fatty acid experiments varied from 9 to 34 μg/100 g, 24 to 61 μg/100 g and 60 to 138 μg/dl, respectively, from low to high levels. In the oxidised lipid experiments, content of oxycholesterols varied from 16 to 52 μg/100 g, 14 to 108 μg/100 g and 52 to 269 μg/dl in meat, liver and plasma, respectively. As a consequence, meat products from rabbits fed a diet containing higher levels of trans fatty acids or oxidised lipids may result in higher intakes of cholesterol and oxycholesterols by humans.     

Sensory and chemical evaluation of winey-vinegary defect in virgin olive oils

Winey-vinegary sensory defect was evaluated in virgin olive oil samples from a sensory and chemical point of view. Qualitative and quantitative differences were found in the profile of volatiles of extra-virgin olive oil samples without sensory defects and samples with high intensities of winey-vinegary sensory attribute. Several volatile compounds were found to be correlated to winey-vinegary sensory defect in virgin olive oils, acetic acid and ethyl acetate having correlation coefficients of 0.98 and 0.94 respectively. A synthetic sample was obtained with the sensory characteristics of the winey defect. Samples with low values of winey sensory defect were also studied and the evaluation of the presence of the defect using the content of four volatile compounds only was demonstrated. Received: 5 August 1999 / Revised version: 22 October 1999     

Stability of avocado oil during heating: Comparative study to olive oil

The stability of the saponifiable and unsaponifiable fractions of avocado oil, under a drastic heating treatment, was studied and compared to that of olive oil. Avocado and olive oil were characterised and compared at time 0 h and after different times of heating process (180 °C). PUFA/SFA (0.61 at t = 0) and ω-6/ω-3 (14.05 at t = 0) were higher in avocado oil than in olive oil during the whole experiment. Avocado oil was richer than olive oil in total phytosterols at time 0 h (339.64; 228.27 mg/100 g) and at 9 h (270.44; 210.30 mg/100 g) of heating. TBARs was higher in olive oil after 3 h, reaching the maximum values in both oils at 6 h of heating treatment. Vitamin E was higher in olive oil (35.52 vs. 24.5 mg/100 g) and it disappeared earlier in avocado oil (at 4 vs. 5 h). The stability of avocado oil was similar to that of olive oil.     

A capacitive technique to assess water content in extra virgin olive oils

The present research investigated the correlations between capacitance and water content of extra virgin olive oils (EVOO). A commercial capacitor probe for radio applications and an LCR meter were used for electric tests in the frequency range from 500 Hz to 512 kHz. Seventeen samples of different EVOO with a moisture content ranging from 178 to 1321 mg/kg oil were selected for study. To assess the influence of moisture only, the oil with the maximum water content was filtered down to 288 mg/kg oil and five samples with intermediate water contents were prepared and submitted to electrical measurements. Subsequently, the capacitance of all 17 EVOO samples was measured at selected frequencies.     

Direct determination of phenolic compounds and phospholipids in virgin olive oil by micellar liquid chromatography

A simple HPLC method is reported for fast separation and determination of phenolic compounds (tyrosol, caffeic acid, p-coumaric acid and oleuropeina) and phospholipids (phosphatidylethanolamine and phosphatidylcholine) in virgin olive oil samples. The samples were diluted with 2-propanol and injected into the column directly without previous extraction. Samples with an olive oil content of up to 65% were injected without any problems. The analytes were separated on a C-18 column by a micellar mobile phase containing 0.07 M SDS and 2.5% 2-propanol at pH 3, and were detected at 210 nm. Linear calibration curves [r² > 0.997] were obtained with detection limits ranging from 0.052 to 0.16 μg/g and 1 to 8.6% repeatability for the phenolic compounds. Several virgin olive oil samples were analysed and the recovery values were around 110%.