Carotenoids and triacylglycerols interactions during thermal oxidation of refined olive oil

Carotenoids (β-carotene and astaxanthin) were added to refined olive oils and oxidised in a Rancimat at 110 °C for 1–14 h. Triacylglycerols (TAGs) were found to oxidise much faster in the presence of β-carotene and slower in the presence of astaxanthin, while β-carotene degradation was much faster than that of astaxanthin. Astaxanthin was found to protect the TAGs of olive oils for up to 10 h of thermal treatment. Both carotenoids were found to significantly increase peroxide values at higher exposure time. A total of 11 TAGs oxidised species were identified, including a new class of oxidised species (hydroxy epidioxides), reported here for the first time. The effect of carotenoids on the formation of oxidised TAGs illustrates that the pro-oxidant action of β-carotene was much stronger than that of astaxanthin. We suggest that astaxanthin could be used as an alternative to β-carotene in edible oils fortification and as a food colourant.     

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.     

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.     

The antioxidant capacity and oxidative stability of virgin olive oil enriched with phospholipids

Virgin olive oil (VOO) enriched with phospholipids (soy lecithin) up to the levels present in seed oils (from 2.5 to 10.0 g/kg) was studied as a potential functional food. Lecithin addition slightly increased the concentration of tocopherols and considerably increased K270 values. In the fatty acid composition, an increase of linoleic and a slight decrease of oleic acid were observed, as the decrease of monounsaturated/polyunsaturated fatty acid ratio. The radical-scavenging activity was evaluated by two methods: electron spin resonance spectroscopy using galvinoxyl free radical and VIS spectroscopy measurement of the disappearance of 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical. Results indicate that lecithin addition retards the scavenging activity of VOO that is ascribed to the bipolar character of lecithin and its ability to entrap hydrophilic antioxidants. The effect of lecithin addition on the oxidative stability of VOO was evaluated by the Rancimat method, and a positive linear correlation (r = 0.9849) with induction time was found.     

Stability of virgin olive oil and behaviour of its natural antioxidants under medium temperature accelerated storage conditions

The aim of the present research is to advance the study of virgin olive oil stability, in particular the behaviour of its natural antioxidants during long term storage. The changes undergone by tocopherols and complex and simple phenolic compounds and their antioxidant activity were studied under medium temperature (50 °C) accelerated oxidation conditions over a storage period of 8 months. Different oxygen availability (open and closed bottles, OB and CB) and four different monovarietal Tunisian virgin olive oils (VOO; Chemlali, Chétoui, El Hor and Oueslati) which vary in their fatty acid profile and content of natural antioxidants were employed. Oueslati VOO showed the lowest initial oxidation rate (4.6 PV/week) and as a consequence the highest induction period (IP; 16 days) as compared to the other VOOs studied (initial rate from 7.7 to 12.1 PV/week and IP from 9 to 12 days for El Hor and Chemlali, respectively, in both cases). In all cases the complete depletion of α-tocopherol corresponded with the observed induction period. Since the oxidation rate in the varieties studied is not sufficiently different to explain the great differences in the initial degradation rate observed in the phenolic compounds (mainly between Chétoui VOO, 163 μmol/kg/week, as compared to the other VOO oils, e.g. 6.1 and 2.5 μmol/kg/week, respectively, in Chemlali and El Hor VOOs), a concentration dependent degradation rate of complex phenols is suggested.     

Oxidative stability of olive oil after food processing and comparison with other vegetable oils

The use of olive oil showed an important protection of meat and potatoes when compared with other vegetable oils, with sunflower oil samples being oxidised after 60 min of processing at 180 °C. Olive oil samples were not oxidised, independently of the olive oil quality used. Shelf life was longer for extra-virgin olive oil containing samples and this fact was positively correlated with their higher phenolic content. The radical-scavenging activity of extra-virgin olive oil was higher than for other olive oil samples and was also positively correlated with the phenolic content of the oil. Seed oil antioxidants showed little capacity in delaying the oxidative degradation of seed oils and meat processed with them. However, tocopherol content and the identity of tocopherols present in the oil were shown to have a more important role in the oxidative stability of seed oils than the fatty acid composition.     

Citrus peel extract – A natural source of antioxidant

Citrus peel extract as a natural source of antioxidant was evaluated during 6 months storage of refined corn oil at 25 and 45 °C. Extracts of citrus peel were prepared by refluxing the dried ground peel with ethanol, methanol, acetone, hexane, diethyl ether and dichloromethane. Maximum amount of citrus peel extract was obtained with methanol. Antioxidant activity of methanolic extract was assessed by measuring free fatty acid (FFA) content peroxide value (POV) and iodine value (IV) during 6 months storage of refined corn oil at 25 and 45 °C. After 6 months of storage at 45 °C, corn oil containing 1600 and 2000 ppm citrus peel extract, showed lower FFA contents (1.5% and 1.0%), and POVs (8.38 and 7.0 meq kg⁻¹) and higher iodine values (81, 89) than the control sample (FFA 17.0% POV 101 meq kg⁻¹ IV 47). Refined corn oil containing 200 ppm of butylated hydroxy anisole (BHA) and butylated hydroxy toluene (BHT) showed FFA contents of 2.0% and 1.8%, POVs 17.0 and 12.7 meq kg⁻¹ and IVs 84 and 87, respectively, after 6 months of storage at 45 °C. These results show that methanolic extract of citrus exhibited very strong antioxidant activity, which was almost equal to synthetic antioxidants (BHA and BHA). Therefore, the use of citrus peel extract is recommended as a natural antioxidant to suppress development of rancidity in oils and fats.     

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.     

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.     

Enrichment of table olives with polyphenols extracted from olive leaves

The possibility to increase the nutritional value of table olives using polyphenols extracted from olive leaves was studied. Leaves were subjected to extraction using water with proportions of 1%, 5% and 10% of leaves and various temperatures and times (room temperature/24 h, 40 °C/10 min and 70 °C/5 min). The antioxidant activity of extracts was determined using the Rancimat method and their content in oleuropein and hydroxytyrosol was determined by HPLC. The extract with the highest antioxidant activity and polyphenol content (10% ratio of olive leaves extracted at room temperature for 24 h) was used for the treatment of debittered table olives. The treated and untreated olives were subjected to determination of their α-tocopherol, oleuropein and hydroxytyrosol content. A 457% increase was observed for oleuropein and 109% for hydroxytyrosol content after treatment. Sensory evaluation of treated table olives showed an increase in bitterness. However, treated and untreated table olives showed equal overall acceptability and overall preference.     

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.     

Separation and determination of sterols in olive oil by HPLC-MS

This study presents the first liquid chromatographic method for the identification and quantification of seven phytosterols in olive oil. Sterols were identified and quantified by liquid chromatography with mass spectrometry detection in positive APCI (atmospheric pressure chemical ionisation) mode. The samples were saponified by refluxing with 2 N ethanolic KOH, and the non-saponificable fraction was extracted with diethyl ether. This fraction was subjected to thin layer chromatography (TLC) on silica gel plates and then the band of sterols was isolated and extracted with methanol. Sterols were quantified by LC-MS, on a Waters Atlantis 5 μm dC₁₈2,1 × 150 mm column with a gradient of acetonitrile/water (0.01% acetic acid) at a flow of 0.5 mL min⁻¹; column temperature 30 °C. The method presents values between 123 and 677 ng mL⁻¹ for detection limits, with relative standard deviations between 4.0% and 5.4% at a concentration of 5 mg L⁻¹ for each sterol. Sterol contents were determined in a virgin olive oil, a refined olive oil, an olive-pomace oil and a crude olive-pomace oil.     

Influence of olive paste preparation conditions on virgin olive oil triterpenic compounds at laboratory-scale

The influence of olive paste preparation conditions on the triterpenic content of virgin olive oils from Arbequina and Picual cultivars was investigated. For this purpose, three sieve diameters of the hammer mill (4, 5, and 6 mm), two malaxation temperatures (20 and 30 °C), and two malaxation times (20 and 40 min) were tested. Results obtained showed that for Arbequina oils, a finer crushing level resulted in higher maslinic acid and erythrodiol content. Increasing malaxing temperature and time lead to a rise in both oleanolic and maslinic acid concentration, whereas erythrodiol content increased only for the longer malaxation time. For Picual oils, higher concentrations of oleanolic acid, maslinic acid, and uvaol were obtained by prolonging the paste malaxation time. A finer crushing level resulted also in an increase of maslinic acid content. These findings suggest that virgin olive oil triterpenic composition can be improved by regulating olive paste preparation conditions.     

Stability for olive oil control materials

For the reliability of analytical Quality Control Materials (QCMs), stability studies are essential. In spite of the importance of the stability studies, there is no article relating to QCMs of olive oil. This paper describes an intralaboratory stability study aimed for assuring olive oil QCMs concerning to the physical–chemical characteristics defined in Commission Regulation (EC) No. 1989/2003. The study concluded that, in storage conditions of darkness and low controlled temperature (0–8 °C), critical physical–chemical parameters of the olive oil QCMs, such as acidity level, peroxide value, K-values and total waxes, are stable at least during 24 months (2 years) with, in general, light variability and up trends. Theoretically, according to this study a homogeneous sample olive oil could be used as a QCM during two years if this material were stored in the dark and low temperature. Then, olive oil quality control testing laboratories have an alternative to dispose stable in-house QCMs for the control of their measurements.     

Phenolic content of commercial olive oils

The phenolic composition of commercial virgin olive oils (Picual, Hojiblanca, Arbequina and Cornicabra varieties) was studied by high performance liquid chromatography, sampling oils over 1 year. Oils sold in March displayed the lowest polyphenol concentration, particularly in secoiridoid aglycons. In contrast, lignans and tocopherols concentrations were not affected by sampling date. Among varieties, Picual and Cornicabra oils had slightly higher concentrations of polyphenols than Hojiblanca and Arbequina. Overall, the concentration of polyphenols in commercial Spanish virgin olive oils ranged from 330 to 500 mg/kg oil, which is higher than data reported previously. In contrast, "olive oil" and "pomace-olive oil" (mixtures of refined and virgin olive oils) had much lower concentrations in polyphenols than virgin olive oil, although higher than other edible vegetable oils. Thus, olive oil can be considered a good source of natural antioxidants. Moreover, the polyphenol and tocopherol contents of virgin olive oils were also found useful for the classification of the different commercial monovarietal oils when analysing the data by chemometric methods.     

Sterolic composition of Chétoui virgin olive oil: Influence of geographical origin

The sterol profile of Tunisian virgin olive oils produced from Chétoui cultivar, the second main variety cultivated in the north of the country, grown under different environmental conditions, was established by gas chromatography using a flame ionisation detector. More than ten compounds were identified and characterised. As expected for virgin olive oil, the main sterols found in all Chétoui olive oils were β-sitosterol, Δ5-avenasterol, campesterol and stigmasterol. Cholesterol, 24-methylenecholesterol, clerosterol, campestanol, sitostanol, Δ7-stigmastenol, Δ5,24-stigmastadienol, and Δ7-avenasterol were also found in all samples, but in lower amounts. Most of these compounds are significantly affected by the geographical origin. The majority of the Chétoui virgin olive oils analysed respected EC Regulation No. 2568, and in all cases total sterol amounts were higher than the minimum limit set by legislation, ranging from 1017 to 1522 mg/kg.     

Physicochemical characterisation and oxidative stability of fish oil and fish oil–extra virgin olive oil microencapsulated by sugar beet pectin

Spray-dried microcapsules were prepared at 25% and 50% w/w oil load from sugar beet pectin-stabilised emulsions (pH 3) containing fish oil, and a blend of fish oil and with extra virgin olive oil (1:1 w/w). Microencapsulation efficiencies were high (≥90%). However, deterioration in microcapsule wall integrity and an increase in oil droplet size were observed during storage (25 °C, 0–3 months). Lipid oxidation increased with both increased oil load (P < 0.05) and storage duration (P < 0.05), but was independent of oil composition (P > 0.05). These results suggest that sugar beet pectin functions poorly as a wall material and its residual metal ions exacerbate omega-3 oxidation, despite the presence of endogenous antioxidants found in extra virgin olive oil. Interestingly, under accelerated storage conditions (OxiPres® at 80 °C, 0.5 bar oxygen pressure), microcapsules containing the oil blend showed the best oxidative stability (P < 0.05), irrespective of oil load. A possible explanation for the superior oxidative stability of the microencapsulated oil blend at high storage temperature is discussed.     

The use of polyphenolic extract,purified hydroxytyrosol and 3,4-dihydroxyphenyl acetic acid from olive mill wastewater for the stabilization of refined oils: a potential alternative to synthetic antioxidants

Ethyl acetate extracts of olive mill waste water (OMWW) were prepared, under in optimal conditions, using a continuous counter-current extraction unit. The antiradical and antioxidant activities of the OMWW extract as well as pure phenolic compounds identified in this extract were evaluated. Results showed that pure hydroxytyrosol and 3,4-dihydroxyphenyl acetic acid had the highest radical-scavenging effects on 1,1-diphenyl-2-picrylhydrazyl radical and the highest antioxidant activities using the β-carotene linoleate model system.The effect of addition of individual phenolic compounds and OMWW extract to refined olive and husk oils was compared with that of control, BHA and BHT at 50 °C. Unexpectedly, 3,4-dihydroxyphenyl acetic acid had the highest protective effect against oil oxidation. Oils with added 3,4-dihydroxyphenyl acetic acid had lower PV than oils with added hydroxytyrosol, the most studied powerful antioxidant. Moreover, the addition of OMWW extract, at 500 ppm, resulted in lower PV values than BHA, p-hydroxyphenylacetic acid, tyrosol on the control.The results suggested that 3,4-dihydroxyphenyl acetic acid, hydroxytyrosol and OMWW extract possess useful antioxidant properties and may be used as alternatives in the search for natural replacement of synthetic antioxidant food additives.     

On the extraction and antioxidant activity of phenolic compounds from winery wastes

Winery waste (from red winemaking, variety Agiorgitiko) was extracted under various conditions using different solvents. The minimum time required for ensuring maximum extraction of phenols was 180 min at a solvent to sample ratio 9:1 v/w and at pH 1.5. The antioxidant activity of solvent extracts was investigated by DPPH radical scavenging method, by determination of peroxide value on virgin olive oil and by the Rancimat method on sunflower oil. Ethanol extract exhibited the highest antioxidant activity compared to the other solvent extracts, to synthetic food antioxidants BHT, ascorbyl palmitate and to the natural food antioxidant, vitamin E. No correlation was found between antioxidant activity and total phenol content. HPLC analysis of the extracts showed that gallic acid, catechin and epicatechin were the major phenolic compounds in winery waste. Hydroxytyrosol, tyrosol, cyanidin glycosides and various phenolic acids such as caffeic, syringic, vanillic, p-coumaric and o-coumaric acids were also identified.     

Temperature dependence of the autoxidation and antioxidants of soybean, sunflower, and olive oil

Effects of temperature on the autoxidation and antioxidants changes of soybean, sunflower, and olive oils were studied. The oils were oxidized in the dark at 25, 40, 60, and 80 °C. The oil oxidation was determined by peroxide (POV) and p-anisidine values (PAV). Polyphenols and tocopherols in the oils were also monitored. The oxidation of oils increased with the oxidation time and temperature. Induction period decreased with the oxidation temperature; 87 and 3.6 days at 25 and 60 °C, respectively, for sunflower oil. The activation energies for the autoxidation of soybean, sunflower, and olive oils were 17.6, 19.0, and 12.5 kcal/mol, respectively. Olive oil contained polyphenols at 180.8 ppm, and tocopherols were present at 687, 290, and 104 ppm in soybean, sunflower, and olive oils, respectively. Antioxidants were degraded during the oil autoxidation and the degradation rates increased with the oxidation temperature of oils; for tocopherols, 2.1 × 10⁻³ and 8.9 × 10⁻²%/day at 25 and 60 °C, respectively, in soybean oil.