Phenolic compounds of virgin olive oil: influence of paste preparation techniques

An experimental investigation was carried out on olive oils of the Ogliarola Salentina and Coratina cultivars to assess the influence of the two different olive grinding techniques and kneading process on the quality of the oils. The experimental data obtained showed that resistance to oxidation, total phenols and phenolic compounds analysed for HPLC were higher in the Coratina oils than in the Ogliarola oils. The use of hammer-crushers plus kneader rather than stone mills plus kneader always produced significant increases in the total phenols. Resistance to oxidation was assessed by the Rancimat method and showed a significant correlation with the amounts of total phenols and of an unidentified substance (peak I) which was conspicuously present amongst the substances evaluated for HPLC.     

Effect of phospholipids on extraction of hydrophilic phenols from virgin olive oils

Three methods, most frequently used in hydrophilic phenols extraction from virgin olive oils (liquid–liquid, solid-phase with C18 and solid phase with diol-bound sorbents), were applied on virgin olive oils enriched with 2.0–10.0 mg/kg of phospholipids (granular de-oiled soy lecithin). Phospholipids addition significantly decreased the total phenols concentration determined colorimetrically. Liquid–liquid extraction showed the best repeatability and recovery, and the lowest decrease of total phenols extracted in the presence of phospholipids. Extraction rate declined with the increase of phospholipids concentration, but showed a kind of saturation behaviour. Addition of phospholipids (5 g/kg) to various commercial extra virgin olive oils resulted in a different degree of total phenols decrease (from 1% to 45%), probably because of different affinity of phospholipids toward different classes of phenolic compounds. During prolonged contact time between phenols and phospholipids (60-days storage), oxidation monitored by K270 and a decrease of total phenols concentration proceeded more rapidly in the presence of phospholipids.     

Hammer crushers vs disk crushers: the influence of working temperature on the quality and preservation of virgin olive oil

An investigation was carried out using a hammer-crusher and a disk-crusher for olive paste preparation to evaluate the effects of different processing temperatures on the quality of the virgin olive oils obtained. The tests performed showed that hammer-crushing produces a more intense fragmentation of the olive pits than the disk-crusher, thus resulting in a more substantial increase in output temperature. Higher temperatures in the crusher during olive processing lead to a shorter preservation of the oils. All the analytical determinations performed also showed that the oils obtained from hammer-crushed pastes presented a greater degradation than those from disk-crushed pastes. These findings were further confirmed by the oven test results.     

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.     

Use of HPSEC analysis of polar compounds to assess the influence of crushing temperature on virgin olive oil's quality

An experimental trial was carried out to evaluate, by means of determination of polar compounds and their subsequent HPSEC analysis, the influence of the hammer-crusher temperature during the olive paste preparation prior to oil extraction. Olives of Cima di Bitonto cultivar were processed utilising a laboratory-scale hammer-crusher conditioned at three different temperatures (12, 16 and 20 °C). The analytical results showed that the quality of the extracted oils was negatively influenced by increasing the crushing temperature. The oils obtained at higher crusher temperatures were more susceptible to oxidation than the oils obtained with crusher conditioned at lower temperatures. The HPSEC analysis of polar compounds was found to be useful to evaluate the oxidative and hydrolytic degradation levels of virgin olive oils also after slight thermal raising.     

Phenolic compounds in virgin olive oils: influence of the degree of olive ripeness on organoleptic characteristics and shelf-life

 An experimental investigation was performed on virgin olive oils from Coratina and Ogliarola salentina cultivars extracted from green, partially blackened and totally blackened olives in order to evaluate changes in the organoleptic properties and in the shelf-life of the oil. The aim of the investigation was to identify the optimal stage of olive maturation for each cultivar to produce higher quality oils. Routine analyses in accordance with EC regulation no. 2568/91, the determination of phenols by HPLC and induction times were carried out. On the whole, the simple phenolic compounds increased as darker olives were used whereas the hydrolysable phenolic compounds decreased. In both the cultivars, total phenols and induction times were significantly higher in the oils obtained from green olives than in oils from totally blackened olives. Hence, it seems advisable to delay olive harvesting for cultivars usually yielding bitter to pungent oils (e.g. Coratina), but to anticipate harvesting for olives producing sweet tasting oils (e.g. O. Salentina). This would produce less bitter Coratina oils, with organoleptic features which may better fulfil consumers' expectations, and O. Salentina oils more resistant to oxidation. Received: 5 June 2000     

Heat-oxidation stability of palm oil blended with extra virgin olive oil

Rancimat induction time of palm oil (PO), several extra virgin olive oils (EV) and their binary blends have been determined at three different temperatures (120, 130 and 140°C). Analytical composition and oxidation stability of PO/EV blends were found to be a linear combination of the oil partners. Induction time of pure PO was always higher than those of EV oils and blends, in which induction time increased proportionally with the percentage of PO. However, induction time of 80% PO blend was similar to that of pure PO. Fatty acid composition appeared to be the most important factor affecting heat-oxidation stability and a saturated/unsaturated ratio near 1 was the optimally stable composition. Conversely, total phenols had a zero or negative role on the oxidative stability of the blends. Finally, in heat-oxidised oils significant losses of polyunsaturated fatty acids and formation of short-chain fatty acids were recorded.     

The amounts of oxidized and oligopolymeric triacylglycerols in refined olive oil as a function of crude oil oxidative level

The refining process is essential to make edible both lampante olive oils and solvent-extracted vegetable oils. The aim of this work was to evaluate the influence of the crude oil oxidation level and of the standard refining process on the amount of oxidized triacylglycerols (ox-TAG) and triacylglycerol oligopolymers (TAGP) in the corresponding refined oil. A virgin olive oil was let to progressively autoxidize at room temperature and was used at different oxidation levels in the experimental trials. Samples were submitted to the same refining process, utilizing a laboratory-scale pilot plant. The results obtained showed that the steps of the refining process caused the increase of oligomeric oxidation products in the refined oil respect to the corresponding raw oil. In this study the oxidative degradation in the crude oil resulted to be correlated to the final amounts of ox-TAG and TAGP. These findings point out that the final levels of oxidation products in refined oils depend both on the adopted standard refining steps and on the oxidative level of the crude oils. In particular, being ox-TAG highly pro-oxidant substances, the oxidative status of the crude oil can severely affect the shelf-life of the refined oil.     

Composition and stability of olive oil following partial crystallization

Extra virgin olive oils were separated into two fractions, one being liquid at 4 °C and one solid. Each of the oils and their associated fractions underwent analysis for fatty acid composition, analysis of the total antioxidant activity and stability towards oxidation when heated at 150 °C. The solid fraction contained greater amounts of saturated fatty acids, although analysis of the fatty acids on position 2, obtained via a pancreatic lipase treatment, showed similar total levels of unsaturated fatty acids for all fractions. Analysis of the antioxidant components showed that there was a higher proportion associated with the liquid fractions. This trend, in combination with the results of the heating trials of the oils and associated fractions, indicated that the liquid fraction was not more susceptible to oxidation. Hence it is possible to fractionate olive oil to give fractions with onset of melting differing by some 10 °C without compromising stability towards oxidation.     

Possibility of improving the quality characteristics of olive‐pomace oil and enhancing its differentiation from refined olive‐pomace oil

An investigation was carried out to evaluate the oxidative and hydrolytic degradation of 37 olive‐pomace oils marketed in southern Italy and to compare the results with those obtained from 10 deodorised olive‐pomace oils representative of large stocks of oil obtained after the final step of refining. One aim of the research was to ascertain the quality characteristics of commercial olive‐pomace oils; another was to verify whether the legally prescribed addition of virgin olive oil to refined pomace oil, so that the final product may be classified commercially as olive‐pomace oil, was actually sufficient to justify upgrading. The analytical methods used were silica gel column chromatography and high‐performance size exclusion chromatography. The data obtained showed that the final retail olive‐pomace oils had a lower degree of oxidative degradation than the refined oils, as indicated by the lower values obtained when summing the proportions of triglyceride oligopolymers and oxidised triglycerides. Conversely, hydrolytic degradation, which was evaluated by determining diglycerides, proved to be the same in the two categories of oil. The proportions of virgin olive oil added are small, as indicated by the statistically indistinguishable values of triglyceride oligopolymers and free fatty acids obtained. The possibility of setting a limit to the amount of triglyceride oligopolymers present in the commercial category of olive‐pomace oil has been considered. This limit would ensure standardisation of the level of oxidation and, consequently, of the quality of marketed oils and would enhance differentiation between olive‐pomace oil and refined olive‐pomace oil. © 2000 Society of Chemical Industry     

Lipochromes,vitamins, aromas and other components of virgin olive oil are affected by processing technology

A stone mill-integral decanter (SD) olive processing line was compared with a traditional stone mill-press (SP) line, a discontinuous method, that, if properly used, yields high-quality virgin olive oils. With “difficult olives” (not easy to process), the SD line yielded oils characterised by: (1) higher contents of pleasant volatiles, tocopherols, β-carotene, xanthophylls, chlorophylls, pheophytins and waxes; (2) higher values of the 1,2-diglycerides/1,3-diglycerides ratio, integral colour index and chroma; (3) lower contents of phenols, secoiridoids, unpleasant volatiles, aliphatic alcohols, triterpene alcohols and sterols; and (4) lower values of turbidity, brightness and oxidative stability. With “non-difficult olives” (easy to process), whose paste needed to be fluidised with lukewarm water, the SD line yielded oils showing higher contents of pleasant volatiles and tocopherols, lower contents of unpleasant volatiles and comparable contents of phenols and lipochromes. The content of organophosphorus pesticide residues did not depend on the processing method.     

云南11种油料作物油脂主要功能性成分评价

采用索氏抽提仪、气-质联用仪、高效液相色谱仪、紫外分光光度计对云南11种油料作物油脂中植物甾醇、角鲨烯、维生素E、类胡萝卜素和总酚含量进行测定分析。结果表明:植物油脂中的植物甾醇均以β-谷甾醇为主,β-谷甾醇含量最高的为菜籽油,总植物甾醇含量最高的也为菜籽油;橄榄油中角鲨烯的含量最高,达0.637%,明显优于其他植物油脂;红花籽油中维生素E含量最高,达19.90 mg/100 g(以α-生育酚计);花生油中类胡萝卜素含量最高,达18.10 mg/100 g;菜籽油中总酚含量最高,达247.91 mg/kg。通过主成分分析并对11种植物油脂的主要功能性成分综合得分进行排序,得分由高到低为菜籽油>橡胶籽油>花生油>红花籽油>橄榄油>大豆油>青刺果油>油茶籽油>油藤果油>核桃油>澳洲坚果油。因此,如果仅从脂溶性成分来看,菜籽油最优,橡胶籽油次之。     

Valorisation of low quality edible oil with tomato peel waste

The aim of this study is to enrich edible oils with carotenoids and lycopene from tomato purée or tomato peel, an industrial tomato waste. These tomato derivatives were incorporated in refined olive oil, extra virgin olive oil and refined sunflower oil. The incorporation of peel enhanced the concentration of β-carotene and lycopene more than tomato purée. Furthermore, the incorporation of both tomato purée and peel induced better thermal stability of the refined olive oil compared to extra virgin oil and sunflower oil. A decrease on total phenols as well as some prooxidant activity account for this, when tomato purée was incorporated. In our oil preparations, rutin and naringenin, as flavonoids coming exclusively from tomato purée or peel, were detected. The enrichment of oils with tomato carotenoids and lycopene, in particular low quality oils like refined olive oils, might be an alternative approach to elaborate new functional foods.     

Chemical changes of thermoxidized virgin olive oil determined by excitation–emission fluorescence spectroscopy (EEFS)

The fluorophores present in virgin olive oil evolve during any thermoxidation process and thereby fluorescence spectroscopy can be used as a straightforward approach to study the oxidative degree of oils. Samples of heated virgin olive oils collected from a fryer every two hours up to 94 h were analyzed to study their excitation–emission matrix (EEM) and the evolution of the fluorescent composition during the thermoxidation process. The potential usefulness of EEM to study thermoxidized virgin olive oils has been explored. For this purpose, parallel factor analysis (PARAFAC) was used to interpret the results. The emission profile obtained from three-factor PARAFAC model calculated for 47 samples of thermoxidized oil in the range of λ_ex = 250–298 nm and λ_em = 300–700 nm allows the decomposition of the fluorescence landscape in specific information about phenols, pigments and oxidation products respectively. The chemical interpretation from the PARAFAC model was checked with chemical analysis of phenols, tocopherols and chlorophyll pigments.     

Modelling of virgin olive oil extraction using response surface methodology

Malaxation of the paste is the most important step for virgin olive oil extraction because it affects both oil yield and quality. In this work the influence of temperature and mixing time on oil yield, quality parameters and oil composition in photosynthetic pigments and total polyphenols is assessed by using Response Surface Methodology. Seven Picual‐variety olive samples from two consecutive seasons, with different maturity index, were used. Results show that temperature and malaxation time exert a positive influence in olive yield, with optimal values ranging from 20.1 to 32.2 °C and from 73.3 to 90 min. Oil quality decreased slightly as temperature and time of malaxation were increased. Top quality oils were obtained below 30 °C and shorter mixing time. The oil content in photosynthetic pigments increased with temperature and mixing time, while total polyphenols increased with temperature but decreased with mixing time.     

Performance of virgin olive oil and vegetable shortening during domestic deep-frying and pan-frying of potatoes

The performance of virgin olive oil and a commercial vegetable shortening was investigated during 10 successive pan-fryings of potatoes at 180 °C for a total period of 60 min and during 10 successive deep-fryings at 170 °C for a total period of 120 min. These are typical conditions of Greek domestic cooking. For both the oils tested the effect of pan-frying on K232, K268, K316, α-tocopherol, total polar artefacts, Rancimat induction times, octanoic acid formation and linoleic acid decomposition was worse than the effect of deep-frying on the same variables. The same was true for visible spectrum and total phenols in virgin olive oil. No systematic variations of oleic acid, refractive index and trans -isomers of fatty acids were detected. None of the oils reached the limit of 25–27% total polar artefacts. Both oils performed similarly during pan-frying, while virgin olive oil performed better during deep-frying. A very strong correlation between octanoic acid formation and total polar artefacts in the whole data set was observed.     

Influence of olive storage period on volatile compounds and oil quality of two Tunisian cultivars of Olea europea,Chemlali and Chetoui

Olives (Olea europaea cv. Chemlali and Chetoui) used for oil production were stored, in plastic containers, at 5 °C for four different periods (0–3 weeks) before oil extraction. After storage, the oils were extracted from the fruits, and the acidity, peroxide value, coefficients of specific extinction at 232 and 270 nm, stability, pigments, total phenols, fatty acids, and volatile compounds were determined. The results showed that storage of fruits produced losses in the olive oil quality. During storage, a marked decrease in total phenols content was observed. The cultivar richer in phenols (862.16 mg kg^?1 in Chétoui) had a lower loss (25%). On the contrary, in Chemlali olive oil, the starting value of 728.52 mg kg^?1 decreased to 469.25 mg kg^?1, with a loss of 35%. Chétoui and Chemlali olive oils presented the highest oxidative stability before storage (58.76 and 47.05 h, respectively), while the lowest values were recorded using olives stored for 3 weeks (54.46 and 43.43 h, respectively). The changes in the volatile bouquet were determined using headspace solid phase microextraction (HS‐SPME). Thirty compounds were characterised by GC–FID and GC–MS. Compounds belonging mainly to alcohols, esters, aldehydes, ketones and hydrocarbons chemical classes characterised the volatile profiles.     

Potential use of extra virgin olive oil in bakery products rich in fats: a comparative study with refined oils

The lipid fraction of bakery products undergoes a significant degradation during baking, with an increase in undesirable oxidised substances, that can act as catalysts for further oxidative reactions during storage reducing the product shelf life. The use of extra virgin olive oil in bakery products rich in fat in place of refined oils was studied, assessing the evolution of the oxidative and hydrolytic degradation during storage. Two‐way analysis of variance, followed by Tukey's HSD test for multiple comparisons, covariance and principal component analyses were carried out to compare the effect of the type of oils. The data obtained showed that the evolution of the oxidation levels in the analysed samples during storage was related to the type of oil used in the production process. Particularly, the use of extra virgin olive oil led to significantly lower values of hydroperoxides, ultraviolet absorption constants, triacylglycerol oligopolymers and oxidised triacylglycerols.     

Influence of different irrigation strategies in a traditional Cornicabra cv. olive orchard on virgin olive oil composition and quality

The olive tree is generally grown under rain-fed conditions. However, since the yield response to irrigation, even with low amounts of water, is great there is increasing interest in irrigated agriculture. The main goal of this study was therefore to optimize sustainable irrigation conditions in the Cornicabra olive cultivar grown in Castilla-La Mancha, a region where the aquifers are over-exploited, and to study the effect of different irrigation strategies on the composition and quality of Cornicabra virgin olive oil. Different irrigation treatments, based on regulated deficit irrigation (RDI), 100% ET_c, 125% ET_c, and rain-fed as control, were applied to a traditional olive orchard (cv Cornicabra) in a randomized complete-block design with four replications. The average olive production of the trees grown under rain-fed conditions was much lower, about 35%, than that obtained by applying the different irrigation treatments studied, between which practically no difference were observed. The total phenol content, which affected the sensory bitterness in the oils, decreased significantly as the amount of supplied water increased. This is very relevant, as high levels of phenols, typical of Cornicabra virgin olive oils, may decrease consumer preference. Notably, one of the RDI strategies produced olive oil similar in composition and quality to that obtained by 100% ET_c but with reduced water usage.     

Influence of olive crushing temperature on phenols in olive oils

An experimental investigation was carried out to evaluate the influence the different temperatures at which olives are hammer-crushed and paste kneaded had on the quality of oil and particularly on the phenolic components. The results obtained showed that temperature influenced the diffusion of phenolic compounds in oil. Greater amounts of hydroxytyrosol, tyrosol, caffeic acid, hydroxycaffeic acid and oleuropeine were measured in oils obtained from previously refrigerated olives. Kneading brought about a reduction of total phenols when it was performed on olives crushed at a higher temperature (18vv°C) while it led to a slight increase when it was executed on pastes of previously refrigerated olives (6vv°C).