Lipoxygenase activity in olive (Olea europaea) fruit

The present work was designed to characterize lipoxygenase activity in olive fruit pulp, in order to determine its significance in the biosynthesis of virgin olive oil aroma. Lipoxygenase activity has been detected in particulate fractions of enzyme extracts from olive pulp subjected to differential centrifugation. The activity in different membrane fractions showed similar properties, with optimal pH in the range of 5.0–5.5 and a clear specificity for linolenic acid, which was oxidized at a rate double that of linoleic acid under the same reaction conditions. The enzyme preparations displayed very low activity with dilinoleoyl phosphatidylcholine, suggesting that olive lipoxygenase acts on nonesterified fatty acids. The enzyme showed regiospecificity for the Δ-13-position of both linoleic and linolenic acid, yielding 75–90% of Δ-13-fatty acid hydroperoxides. Olives showed the highest lipoxygenase activity about 15 wk after anthesis, with a steady decrease during the developmental and ripening periods. Olive lipoxygenase displayed properties that support its involvement in the biogenesis of six-carbon volatile aldehydes, which are major constituents of the aroma of virgin olive oil, during the process of oil extraction.     

茶多酚和维生素C对橄榄油抗氧化性的影响

研究了TP和VC对橄榄油抗氧化作用的影响,结果表明TP对橄榄油的抗氧化作用优于VC,当茶多酚的浓度为0.05%～0.06%时,对增强橄榄油的抗氧化性效果最好,且TP中添加VC有明显的抗氧化增效作用。     

Effect of Temperature,Modified Atmosphere and Ethylene During Olive Storage on Quality and Bitterness Level of the Oil

Mill olives (Olea europaea L. cv. ‘Lechín’), harvested at the green mature stage of ripening, were stored for 72 h under six different storage conditions: in air, in a closed container, and in a closed container with 30 ppm ethylene either at 20 or at 40 °C. The use of 40 °C as the fruit storage temperature reduced oil bitterness, regardless of the atmosphere applied; however, it also induced a significant reduction in stability and pigment content of the oil extracted. At 20 °C, mill olives stored under air supplemented with 30 ppm ethylene engendered oils with middle bitterness intensity, whereas the oils obtained from fruit stored similarly, but without ethylene, or in an open container exhibited a strong intensity of this sensory attribute. Fruit respiration in the closed containers caused a CO₂ accumulation and an O₂ decrease in the storage atmosphere. This CO₂ concentration was increased by the previous ethylene addition, but O₂ presence did not suffer an additional reduction. The use of modified atmospheres in fruit storage induced off-flavor development in the oils extracted, producing a significant reduction in the overall grading of their sensory quality.     

Effect of extraction systems on the quality of virgin olive oil

Research has been carried out to ascertai the effects of different processing systems on olive oil quality. Tests were performed in industrial oil mills that were equipped with both pressure and centrifugation systems. Results show that oils extracted from good-quality olives do not differ in free fatty acids, peroxide value, ultraviolet absorption and organoleptic properties. Polyphenols ando-diphenols contents and induction times are higher in oils obtained from good-quality olives by the pressure system because it does not require addition of water to the olive paste. The centrifugation system requires the addition of warm water to the olive paste and helps to obtain oils with a lower content of natural antioxidants. Oils obtained from poorquality or from ripe olives in continuous centrifugal plants are lower in free fatty acids than those obtained by the pressure system. Dr. Mario Solinas is deceased—May 23, 1993.     

Evolution of phenolic compounds in virgin olive oil during storage

Phenolic compounds are of fundamental importance to the shelf life of virgin olive oils because of their antioxidative properties. In this paper, the evolution of simple and complex olive oil phenols during 18 mon of storage is studied by high-performance liquid chromatography (HPLC) analysis. The olive oils under examination were from various olive cultivars, harvested in two sectors in the same region at different stages of ripeness. The findings indicate that it is not the variety but rather the ripeness of the olives and the soil and climate that influence the phenol composition of virgin olive oil. In addition, a positive correlation was found between the age of the oils and the tyrosol to total phenols ratio. Lastly, gas chromatography-mass spectrometry analysis confirmed that the unidentified peaks detected by HPLC were of a phenolic nature.     

Change in the natural ratio between chlorophylls and carotenoids in olive fruit during processing for virgin olive oil

Different varieties of olives from different sources, harvested in a similar ripeness state, have been characterized by their chlorophyll and carotenoid pigment profile and content. Pigment richness is inherent to the variety and enables great differences or similarities to be established between them. In all the fruits, ripening involves pigment loss, with the disappearance of chlorophylls always being slightly greater than that of carotenoids. However, independently of variety and the different pitment content of the fruits, the ratio between chlorophylls and carotenoids tends to remain more or less constant, within a range of 2.5 to 3.7 mg total chlorophyll/mg total carotenoid. Pigment loss caused by the extraction process is more marked for the chlorophyll fraction than for the carotenoids, changing the ratio in the oil to around one unit, whatever the variety of soruce fruit.     

Iron chlorosis in olive in relation to soil properties

Chlorosis due to iron (Fe) deficiency is becoming severe in olive (Olea europaea L.) trees growing on some highly calcareous soils in southern Spain. We investigated the relationships between the incidence of Fe chlorosis in three olive varieties (`Hojiblanco', `Manzanillo' and `Picual') and soil properties. Leaf chlorophyll content, estimated by the mean value of three SPAD measurements during the growing season, was poorly correlated with soil carbonate content and reactivity. In contrast, it was significantly correlated with the clay content and with the amounts of Fe extracted with oxalate (Fe_ox), citrate/ascorbate (Fe_ca), and diethylendiaminepentaacetid acid (Fe_DTPA). This suggests that the content and reactivity of poorly crystalline Fe compounds play an important role in Fe nutrition. The three olive varieties did not differ significantly in their susceptibility to Fe chlorosis. Soil test critical levels separating chlorotic and non-chlorotic trees were 300 g clay kg^–1 soil and 0.35 g Fe_ox kg^–1 soil.     

The presence of oxidizing enzyme activities in virgin olive oil

Samples of Greek virgin olive oils were examined for the presence of proteins and oxidative enzyme activities. All oil samples tested contained detectable amounts of protein, as well as lipoxygenase and polyphenol oxidase activities. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and size-exclusion chromatography of olive oil extracts revealed the presence of low-molecular-mass (10–40 kDa) silver-staining and ultraviolet-absorbing components, respectively. Both lipoxygenase and polyphenol oxidase catalytic activities were heat- and protease-sensitive, and they expressed Michaelis-Menten kinetics.     

Argan oil-in-water emulsions: Preparation and stabilization

We prepared stable oil-in-water emulsions of argan oil with two different types of mixtures of nonionic emulsifiers. Three different types of oil (Israeli argan oil, Moroccan argan oil, and soybean oil) were emulsified with mixtures of Span 80 and Tween 80. The optimum HLB value for argon oil was 11.0 (±1.0). The argan oil-in-water emulsions were stable for more than 5 mon at 25°C. Synergistic effects were found in enhancing stability of emulsions prepared with sucrose monostearate. The origin of the oil and the internal content of natural emulsifiers, such as monoglycerides and phospholipids, have a profound influence on its interfacial properties and on the stability of the argan oil-in-water emulsions.     

Rapid evaluation of olive oil quality by NIR reflectance spectroscopy

NIR spectroscopy calibrations have been developed for a range of quality parameters in olive oil, including FFA, PV, polyphenol content, induction time, chlorophyll, and the major FA. A set of 216 olive oil samples from throughout the Australian olive-growing areas were used to provide a representative range of quality. The variation in the oils tested virtually covered the range of the chemical standard limits described by the International Olive Oil Council. A FOSS NIRSystems^® 6500 spectrophotometer with a liquid cell holder was used. Multiple correlation coefficients squared (R ²) for minor components stearic acid (0.86), and linolenic acid (0.85) were relatively low because the concentration range is very narrow compared with the reproducibility of the reference method. However, the major FA, oleic (0.99) and linoleic (1.00), FFA (0.97), and chlorophyll (0.98) provided high levels of accuracy. All of the parameters measured were sufficiently accurate for routine screening of olive oil.     

The role of endogenous amphiphiles on the stability of virgin olive oil-in-water emulsions

Stable virgin olive oil-in-water emulsions were prepared using total endogenous surface-active components derived from oil as emulsifying agents, and the interfacial properties of the emulsion droplets were examined. The amount of oil extracted into the aqueous buffer increased with buffer pH, with the most stable emulsions being formed at pH 7.5. Light microscopy of the emulsions revealed the presence of spherical droplets with diameters ranging from 1.5 to 3 μm. Their surface was negatively charged at pH 7.5, as confirmed by the effect of ions and polycations. Potassium chloride, Ca²⁺, and spermine induced rapid aggregation (as monitored by the turbidity change and by light microscopy), showing their maximal effect at 1 M, 4 mM, and 60 μM, respectively. Papain treatment of the emulsion particles rapidly induced particle aggregation, suggesting the destruction of stabilizing structural olive oil proteins. Unlike papain, treatment with phospholipase C did not result in an appreciable turbidity change. Treatment with soybean lipoxygenase slightly increased the turbidity of the emulsion. The interaction of linoleate-Tween 20 mixed micelles with emulsion droplets produced turbidity, which was maximal at a neutral pH, whereas interaction with proteolyzed and lipoxygenase-treated droplets induced both a significant increase in turbidity and a red shift to a different absorption maximum of the system as compared with those of the untreated emulsion.     

Effect of fruit storage conditions on olive oil quality

"Koroneiki" olive fruit from trees grown in Crete were stored under five different conditions (0°C, air; 5°C, air; 5°C, 2% O₂+5% CO₂; 7.5°C, air; 7.5°C, 2% O₂+5% CO₂). Oil was obtained from fruit immediately after harvest and after fruit storage for 30 and 60 d. Olive oil quality was evaluated by determining acidity, peroxide value, absorption coefficients (K₂₃₂, K₂₇₀), phenol and chlorophyll content, fatty acid composition, and the resistance to oxidation by oven test. Olives stored at 7.5°C, even for 30 d, deteriorated from fungus development, and the obtained oil was of inferior quality with high acidity, peroxide value, and absorption coefficients. The same oil had high chlorophyll and phenol content, resulting in good oil resistance to oxidation. Olive oil from fruit stored at 0 or 5°C for 30 d had acceptable acidity, peroxide value, and absorption coefficients, but showed low resistance to oxidation, which was attributed to low chlorophyll and phenol content. This condition is further attributed to chilling injury caused by low storage temperatures. During storage, all treatments resulted in an increase of oleic acid, partly as a result of linoleic acid oxidation.     

The triacylglycerol structure of olive oil determined by silver ion high-performance liquid chromatography in combination with stereospecific analysis

The compositions of positionssn-1,sn-2 andsn-3 of triacylglycerols from “extra-virgin” olive oil (Olea europaea) were determined. The procedure involved preparation of diacyl-rac-glycerols by partial hydrolysis with ethyl magnesium bromide; 1,3-, 1,2- and 2,3-diacyl-sn-glycerols as (S)-(+)-1-(1-naphthyl)ethyl urethanes were isolated by highperformance liquid chromatography (HPLC) on silica, and their fatty acid compositions were determined. The same procedure was also carried out on the five main triacylglycerol fractions of olive oil after separation according to the degree of unsaturation by HPLC in the silver ion mode. Although stereospecific analysis of the intact triacyl-sn-glycerols indicated that the compositions of positionssn-1 andsn-3 were similar, the analyses of the molecular species demonstrated marked asymmetry. The data indicate that the “1-random, 2-random, 3-random” distribution theory is not always applicable to vegetable oils.     

Release of ethylene from pruned olive logs: Influence on attack by bark beetles (Coleoptera,Scolytidae)

In recently pruned olive logs, an increase in ethylene release has been observed between 48 and 72 hr after pruning. The values reached, as well as the duration of ethylene release, varied greatly from one log to another. PioneerPhloeotribus scarabaeoides females have shown a preference for logs in which ethylene emission was higher. In logs treated with ethrel, a significant increase in ethylene emission was observed, together with a greater period of release. Therefore, the use of logs treated with ethrel could be of great importance in the control of this pest of olive trees.     

Chemiotropic behavior of female olive fly (Bactrocera oleae GMEL.) onOlea europaea L

An interpretation is given of a number of observations on the chemiotropic behavior ofBactrocera oleae in connection with olive maceration water and the fly's return to the olive groves after the first summer rains. To this end, the headspace of both maceration water and leaf leaching water, simulating rainfall, were examined. In both cases, the presence of ammonia, which is generally known to attract fruit flies (Diptera, Tephritidae), was detected and, for the first time, in addition to other compounds that are inert for the fly, the presence of styrene was also detected. This aromatic hydrocarbon was found to be a strong attractant. It is shown that both ammonia and styrene are products of the metabolism of microbial flora present on the olive and leaf surface.     

High-performance liquid chromatography of selected phenolic compounds in olive oils

A reverse-phase high-performance liquid chromatographic technique with isocratic elution has been developed to separate and quantitate the major phenolic compounds of the hydroalcoholic extracts of olive oils. Hydroxytyrosol, tyrosol, caffeic acid,p-hydroxyphenylacetic acid and homovanillic acid were analyzed on a μBonapak C18 column with an acetonitrile/water/acetic acid (20:90:0.18, vol/vol/vol) mixture as a mobile phase. Electrochemical detection provided selectivity as well as sensitivity. The method was applied to the analysis of the most important phenolic compounds in olive oils.     

The influence of variety and harvest time on the bitterness and phenolic compounds of olive oil

The influence of harvest time on the intensity of bitterness and the level of phenol compounds in olive oil from the region of western Istria, obtained from 2 local (Bianchera and Busa) and one introduced, Italian variety (Leccino) was studied. Olive fruits were harvested at 3 different harvesting periods, during 4 successive crops seasons. Immediately after harvesting, the fruits were processed under the same conditions in a pilot plant. Basic quality parameters, the content of total polyphenols, o‐diphenols and the intensity of bitterness were determined in oil samples. Samples of oil obtained from the Bianchera and Busa varieties were additionally tested for stability at elevated temperature (98 °C) and under the influence of UV‐light. The results elaborated statistically showed the level of phenol compounds and the intensity of bitterness to be significantly influenced by both the harvest time and olive variety, with the influence of harvest time being more pronounced. The applied tests for accelerated deterioration of oil indicated a more rapid increase in the peroxide value in oil samples of both varieties exposed to UV‐light than in those exposed to elevated temperature. Both tests showed better stability of the oil obtained from the Bianchera variety.     

Direct and mediated effects onBactrocera oleae (Gmelin) (Diptera; Tephritidae) of natural polyphenols and some of related synthetic compounds: Structure-activity relationships

Among the main polyphenols occurring in olive oil vegetation waters (VW), catechol showed the most deterrent action on the oviposition ofBactrocera oleae (Gmelin); 4-methylcatechol was less active, whereas hydroxytyrosol and tyrosol were inactive. In contrast, synthetico-quinone was found to be stimulant at 7.5 × 10^–2 M. Two other synthetic derivatives of catechol, diacetylcatechol and guaiacol, were also deterrent, suggesting these compounds undergo a biochemical transformation into catechol by means of the bacterial symbionts ofB. oleae. VW and their phenolic extracts showed deterrence only when highly concentrated, while natural olive juice was strongly deterrent. Experiments carried out to evaluate the effect of olive juice and catechol on the fecundity ofB. oleae showed that they strongly reduce this function. Moreover, the possible utilization of VW and their bioactive polyphenols in protection of olives againstBatrocera oleae is discussed.     

Olea europaea Volatiles attractive and repellent to the olive fruit fly (Dacus oleae,Gmelin)

Comparative study of the headspace (HS) composition from olive leaves, olives of varying degrees of ripeness, and crushed olives revealed significant quantitative and qualitative differences. Three different methods were employed to test the effect of the substances identified on the behavior ofDacus oleae gravid females. Attractive/repellent features were tested by presenting the insects with olfactory choices of a water solution of the test chemicals examined, water (blank), and a highly attractive (control) solution of olive maceration water (MW). Toluene and ethylbenzene, present in leaf and half-ripe olive HIS proved attractive, while (E)-2-hexenal emitted by the crushed olives was found to be decidedly repellent. An oviposition stimulation/deterrence test was carried out on olives placed in proximity to test chemicals under examination in water solution, with olives from the same crop serving as control. In the oviposition test-pinene, mostly emitted by the leaves and half-ripe olives, emerged clearly as an activant,p-xylene, myrcenone, ethylbenzene,n-octane ando-xylene as weak activants. (E)-2-hexenal and hexanal, both emitted by the crushed olives, displayed an oviposition deterrent effect. The highly repellent property of (E)-2-hexenal was again confirmed in this test.     

Oxidative stability of virgin olive oils

An investigation was carried out on virgin olive oils of the Gentile (Larino), Gentile (Colletorto), Coratina, and Leccino varieties, harvested at different times, to assess their oxidation stability. The olive oils were analyzed by means of peroxide, K_232′ and K₂₇₀ values at 1, 6, 12, and 18 mon of storage in green bottles, in the dark, at temperatures ranging from a mean of 6°C in winter to 12°C in summer. A subsample was also oven-tested at 75°C and then analyzed on a weekly basis using the same oxidative parameters. The less ripe the olives (harvested in the same area during 1 mon), the more resistant the olive oils were to forced oxidation. The amount of total phenols in the oils was found to be directly related, even if to a low degree, to the oleuropein content in the olives and inversely related, to the same degree, to (3,4-dihydroxyphenyl)ethanol. The latter is a derivative of oleuropein; (3,4-dihydroxyphenyl)ethanol content increases as the olives ripen, but it is very low in fresh virgin olive oils, owing to the hydrophilic nature of the phenolic alcohol, which goes mainly into the waste-water during processing. Among the varieties considered, Coratina oils showed the highest resistance to forced oxidation because of their high total phenol content.