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.     

二相离心加工工艺对初榨橄榄油理化指标和氧化稳定性的影响

橄榄油的品质不但与品种有关,还受加工工艺的影响。以‘豆果’‘鄂植8号’‘克罗莱卡’3个品种油橄榄果为原料,研究了二相离心加工工艺对初榨橄榄油脂肪酸组成、色度、酸值、过氧化值、紫外吸光度、微量伴随物、抗氧化能力和氧化稳定性的影响,并与三相离心加工工艺进行对比。结果表明:在融合温度30℃、融合时间45 min条件下,初榨橄榄油的品质较好;‘克罗莱卡’初榨橄榄油中多酚含量最高,氧化稳定性最好,与三相离心加工工艺相比,二相离心加工工艺生产的初榨橄榄油多酚含量显著提高。     

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.     

Effects of olive paste fast preheating on the quality of extra virgin olive oil during storage

The olive paste obtained after crushing was fast preheated under different time/temperature conditions and then malaxed in an industrial oil mill (600 kg Frantoio/Leccino olive blend). Legal parameters (peroxides, free acidity and sensory panel), oil yield, total phenolic content, oxidative stability and phenolic profile were monitored during 12 months of storage of the virgin olive oil (VOO) kept in closed bottles in the dark. A fast preheating not longer than 72 s at 38 °C without malaxation lead to an extra VOO with a shelf-life of at least 12-months, similarly to the traditional EVOO obtained with malaxation. A fast preheating not longer than 72 s at 38 °C followed by 10 min malaxation lead to an EVOO with a ‘mild’ sensory profile and a shelf life of at least 12-months. Thus, the use of a specific designed fast preheater instead or before (a shortened) malaxation allows to obtain an EVOO with a low bitter/pungent attribute from olives which are rich of (sometimes unpleasant) phenolic compounds with the aim to meet the preference of targeted groups of consumers. Time and temperature of fast preheating are the critical parameters of the process.     

Shelf-life prediction of olive oils using empirical models developed at low and high temperatures

Induction period of the formation of hydroperoxides and conjugated dienes at 50 °C and oxidative stability index at 100–130 °C as the oxidative stability measures of different types of olive oils with a wide range of chemical compositions were determined. Regression models (R² ? 0.95) developed at low and high temperatures showed different contributions of compositional variables (the ratio between monounsaturated and polyunsaturated fatty acids, the content of total tocopherols and phenolics, peroxide value, acid value, and total polar compounds content) to the oxidative stability measures. To estimate the shelf-life of olive oils at low temperature, three empirical models with errors of ±1.5%, <±10%, and ±21.2% were developed.     

Kneading olive paste from unripe ‘Picual’ fruits: I. Effect on oil process yield

Olive growers start earlier to harvesting in order to obtain high quality oils, however unripe olives show different characteristics affecting technological and rheological properties. This work is aimed to study the effect of malaxation conditions on process oil yield for unripe ‘Picual’ olives. Experiments were carried out using Picual fruits harvested at early dates for three consecutive crops seasons. The malaxation conditions assayed using a factorial design were: time (60, 90 min), temperature (18, 30, 40 °C) and micronised talc addition (0, 1%). Olive paste from unripe Picual fruit are classified as difficult pastes. The main factor affecting oil yield was the crop year, while for each crop year the effect of each factor varied considerably. Results indicated as increasing time and temperature gave lower pomace oil losses although its effect varied on crop year. Micronised Natural Talc addition lowered pomace oil content on dry weight. Therefore for early harvesting dates knowing olive characteristics ‘on line’ is essential to adapt the kneading conditions.     

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.     

Differential scanning calorimeter application to the detectionof refined hazelnut oil in extra virgin olive oil

The potential application of differential scanning calorimetry (DSC) to verify adulteration of extra virgin olive oil with refined hazelnut oil was evaluated. Extra virgin olive oil and hazelnut oil were characterised by significantly different cooling and heating DSC thermal profiles. Addition of hazelnut oil significantly enhanced crystallisation enthalpy (at hazelnut oil ?20%) and shifted the transition towards lower temperatures (at hazelnut oil ?5%). Lineshape of heating thermograms of extra virgin olive oil was significantly altered by hazelnut oil addition: a characteristic exothermic event originated at −27 °C in extra virgin olive oil and progressively disappeared with increasing hazelnut oil content, while the major endothermic peak at −3.5 °C broadened (at hazelnut oil ?40%) and the minor endothermic peak at 8 °C shifted toward lower temperatures (at hazelnut oil ?5%). The preliminary results presented in this study suggest that DSC analysis may be a useful tool for detecting adulteration of extra virgin olive oil with refined hazelnut oil.     

Emissions of volatile aldehydes from heated cooking oils

Emissions of volatile organic compounds, including aldehydes, formed during heating of cooking oils: coconut, safflower, canola, and extra virgin olive oils were studied at different temperatures: 180, 210, 240, and 240 °C after 6 h. Fumes were collected in Tedlar^® bags and later analysed by GC–MS. The emissions of volatiles were constant with time and increased with the oil temperature. When the temperature of the oil was above its smoke point, the emission of volatiles drastically increased, implying that oils with low smoke point, such as coconut, are not useful for deep-frying operations. Canola was the oil generating the lowest amount of potentially toxic volatile chemicals. Acrolein formation was found even at low temperatures, indicating that home cooking has to be considered as an indoor pollution problem.     

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.     

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.     

Effects of processing techniques on the natural colourings and the other functional constituents in virgin olive oil

The effects of two new enzyme processing aids, Bioliva and Rapidase adex D, and that of the olive paste malaxation temperature factor on the composition of natural colourings (chlorophylls, xanthophylls, and carotenes) and the chromatic parameters (chroma, brightness, and hue) have been investigated in virgin olive oils. Other major analytical variables (secoiridoid derivatives, tocopherols, volatiles, sensory scoring, oxidative stability, and glycerides) have also been evaluated. The analysed oil samples were obtained by processing in the experimental oil mill at an industrial level three olive varieties (Caroleo, Leccino, and Dritta). The two enzyme complexes (Rapidase adex D more markedly) affected the values of green and yellow pigments and colour index, as well as the profile of other functional analytical fractions, owing to their effective action on the hypoderm and parenchyma tissues of the fruits. This resulted in an enhanced release of lipochromes and other bioactive non-glyceridic compounds and in a greater accumulation of them into the oil phase. Increasing malaxation temperatures in the range of 20–30 °C resulted in an increase of the concentrations of lipochromes and other functional unsaponifiable components (excluding volatiles) in the oils. An increase of the temperature to 35 °C did not enhance the level of these compounds. On the contrary, the oxidation and other degrading processes might be accelerated.     

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.     

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.     

Changes in the quality of fish oils due to storage temperature and time

The effects of storage temperature on oil quality of various fishes were examined. Fish oils extracted from horse mackerel, shad, garfish and golden mullet were used in oil analyses. Crude fish oils obtained by a solvent extraction method were stored at +4 °C and −18 °C. Chemical quality of the oils was evaluated with various parameters, including iodine, ester, acid, saponification, peroxide, and thio-barbituric acid values and unsaponifiable matter at various time intervals for 150 days of storage. All quality parameters, except iodine and ester values, increased during storage at both of temperatures. Sample oils stored at +4 °C preserved acceptable characteristics for 90 days. Acceptability tolerance was found to be 120 days for shad oil and 150 days for golden mullet, garfish and horse mackerel oils stored at −18 °C. The highest oxidative deterioration was observed in shad oils. Among all samples, garfish oil showed the greatest stability against oxidation.     

Influence of the malaxation time and olive ripening stage on oil quality and phenolic compounds of virgin olive oils

The main objective of this study was to evaluate the influence of the malaxation time (Mt) and ripening stage on oil quality and phenolic compounds of Hojiblanca and Picual virgin olive oils. In both varieties of oil, phenolic content and oxidative stability decreased as ripening progressed. The total level of tocopherols diminished by up to 40% as fruit ripened. The compositions of palmitic, stearic, lignoceric, oleic, linoleic and linolenic acids were significantly influenced by the ripening process. The present work shows that an increased Mt promoted the increase of free acidity (up to 13.3%) and tocopherols (up to 11.6%) and negatively affected the oxidative stability and the concentration of phenols. Further research is required to determine ripening stages and malaxation conditions for all olive oil varieties to achieve a satisfactory balance between the improvement of both oil yield and oil quality and composition.     

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.     

Enzyme inactivation kinetics and colour changes in Garlic (Allium sativum L.) blanched under different conditions

The inactivation kinetics of the enzymes peroxidase, polyphenoloxidase and inulinase and changes in the color parameters L^∗, a^∗ and b^∗ of garlic cloves cut in slices, were studied during steam blanching at 100 °C and water at 80 and 90 °C. The garlic cloves were peeled, cut into slices and distributed uniformly in metal baskets and one batch placed in an autoclave generating steam at a temperature of 100 °C; and the others in water baths at 80 and 90 °C. The best blanching conditions were in steam for 4 min, where no changes in texture were observed, and the enzymatic activities were reduced by 93.53%, 92.15% and 81.96% for peroxidase, polyphenoloxidase and inulinase, respectively. Under these conditions the inulin concentration reduced by 3.72%. The color parameter L^∗ increased with increase in blanching time, the samples becoming lighter in color, and the parameters a^∗ and b^∗ decreased, obtaining slices that were greener and bluer.     

Changes in volatile compounds and oil quality with malaxation time of Tunisian cultivars of Olea europea

While there has been considerable work examining the effect of malaxation time on different characteristics of olive oils, there have been few that deal with all the major aspects. Here, the influence of malaxation time was evaluated using major local Tunisian (cv. Chemlali and Chetoui) cultivars. Standard characteristics were measured as well as detailed analyses of volatile compounds were conducted. Headspace solid‐phase microextraction (HS‐SPME) was applied to the analysis of volatile compounds of virgin olive oils from Chemlali and Chetoui varieties with differing malaxation time. Twenty‐seven compounds were characterised by GC‐FID and GC–MS. Compounds belonging mainly to alcohols, esters, aldehydes, ketones and hydrocarbons chemical classes characterized the volatile profile. Significant differences in the proportion of volatiles from oils of different malaxation time were detected. The results suggest that besides genetic factors, malaxation time influences volatile formation. The main variables that were affected by malaxation time were the total amount of phenols and composition of the volatile compounds. At malaxation time of 30 min, Chemlali and Chetoui olive oils presented the highest total phenol content (244.19 and 877.63 mg kg^?1, respectively), while the lowest content was observed at 60 min from regardless of cultivars. In turn, this influenced the oxidative stability and peroxide value. It was also clear that the cultivars behaved differently and this prevented general conclusions being made for all of the quality characteristics.     

Influence of malaxation temperature and time on the quality of virgin olive oils

To study the influence of operative conditions adopted during the malaxation of pastes on the quality of resulting oils, we compared sensory characteristics, secoiridoid compounds and the volatile composition of oils extracted from homogeneous batches of olive fruits from Coratina and Frantoio cultivars by using different malaxation times and temperatures. Malaxation time, and especially temperature, negatively affected the intensity of sensory attributes and the content of secoiridoid compounds, modified the composition of metabolites arising from lipoxygenase (LOX) pathways, reducing volatile compounds displaying pleasant sensations and increasing those giving less attractive perceptions, and also elevated the production of 2-methyl butanal and 3-methyl butanal through amino acid conversion. Low temperatures and times, ranging between 30 and 45 min, according to the rheology of the olive pastes, were the optimal operative conditions for the malaxation.