Characterization of olive paste volatiles to predict the sensory quality of virgin olive oil

One of the main challenges that virgin olive oil producers face today is an accurate prediction of the sensory quality of the final product prior to the milling of the olives. The possibility that olive paste aroma can be used as a predictive measurement of virgin olive oil quality is studied in this paper. The study was centered on distinguishing the aroma of olive pastes that produced virgin olive oils without sensory defects from the aroma of olive pastes the virgin olive oils of which showed sensory defects. Olive pastes were analyzed by solid‐phase microextraction‐gas chromatography and a sensor system based on metal oxide sensors. Forty‐four volatile compounds were identified in olive pastes, all of them being also present in virgin olive oil. Six volatile compounds – acetic acid, octane, methyl benzene, (E)‐2‐hexenal, hexyl acetate and 3‐methyl‐1‐butanol – distinguished both kinds of pastes with only five misclassified samples. Five metal oxide sensors were able to classify the olive pastes with only two erroneous classifications.     

Effect of location on virgin olive oils of the two main Tunisian olive cultivars

The olive oil content in phenolic compounds depends on the variety of the fruit used for its extraction as well as on the predominant climate conditions in the tree cultivation area. Here, we report on the characterization of virgin olive oil samples obtained from fruits of the main Tunisian olive cultivars Chemlali and Chétoui, grown in three different Tunisian locations, Zaghouan (North), Sousse (Center) and Sfax (South). Chétoui olive oil samples obtained from fruits of olive trees cultivated in Zaghouan and Chemlali olive oil samples obtained from fruits of olive trees cultivated in Sousse were found to have a higher mean total phenol content (1004 and 330 mg/kg, respectively). Olive oil samples obtained from fruits of both cultivars had different phenolic profiles and a higher content in 3,4‐DHPEA‐EDA when the olive trees were cultivated in Zaghouan. Both olive cultivars were found to have different responses to environmental conditions. Chétoui olive oil showed decreased oxidative stability when the fruits were obtained from olive trees cultivated in the center of Tunisia (34.8 h) and in Sfax (16.17 h). Furthermore, statistical data showed that the phenolic composition and oxidative stability of Chétoui olive oil varied more by location than those of Chemlali olive oils.     

Effect of olive paste kneading process time on the overall quality of virgin olive oil

The influence of the olive paste malaxation time on the composition and the industrial output of oil was investigated. To this purpose, three Italian olive varieties (Leccino, Dritta, Caroleo) were processed with a centrifugal system for six malaxation periods (0, 15, 30, 45, 60 and 75 min). The concentrations of the majority of the oil constituents changed during the malaxation. However, these changes were not significant for all of them: the contents of β‐carotene, the major xanthophylls, chlorophylls a and b, pheophytins a and b in the oils increased progressively with increasing malaxing times, whereas the contents of simple and hydrolysable phenols (secoiridoid derivatives), o‐diphenols and total phenols decreased. A significant increase in total volatiles and green volatiles of the lipoxygenase cascade (C₆ aldehydes, C₆ alcohols, C₅ alcohols and C₅ carbonyls) was detected. An opposite trend was observed for the green C₆ esters. As a result, the global analytical quality, flavour, aroma and shelf‐life of the oils were negatively affected. The oil yield increased substantially up to 45 min of paste malaxation times. Beyond 60 min, the yields tended to decrease.     

Quality characteristics of olive leaf‐olive oil preparations

Olive leaf‐olive oil preparations were obtained by vigorous mixing at various levels of addition (5, 10, 15%w/w) of new or mature leaves. After removal of the plant material via centrifugation, quality and sensory characteristics of the preparations were determined. Oxidative stability (120°C, 20 L/h) and DPPH radical scavenging were increased ～2–7 fold depending on the level of leaves used due to enrichment with polar phenols, mainly oleuropein, and a‐tocopherol. The extraction process affected the chlorophyll content and organoleptic traits as indicated by acceptability and preference tests (n = 50). Forty‐four % of the panelists identified a strong pungency in preparations with 15% w/w new leaves. Fifty‐four % of them identified a bitter taste in those with 15% w/w mature leaves, which was attributed to high levels of oleuropein (～200 mg/kg oil). Olive leaf‐olive oil preparations had interesting properties regarding antioxidants present that can attract the interest of a functional product market. Practical applications: The wider use of olive oil and derived products is highly desirable. In this sense, the current study presents data that support introduction to the market of a new specialty olive oil based solely on olive tree products (olive oil and leaves). Thus, in addition to olive oil and olive paste, a new product, that is an olive oil enriched with olive leaf antioxidants, especially oleuropein produced via a “green” technique (mechanical means instead of extraction with organic solvent) can be made available for consumers.     

Effect of olive fruit freezing on oxidative stability of virgin olive oil

Several studies have suggested that the phenolic fraction plays an important role during storage and therefore in the shelf life of virgin olive oil. This investigation examines the effect of freezing olives (–18 °C) before processing into oil on the transfer of the phenolic compounds into the subsequent oil, and the consequential changes in oxidative stability. Oil samples obtained from frozen olives (24 h at –18 °C), crushed with and without preliminary thawing, were compared to a control sample; both oils were obtained using a two‐phase low‐scale mill. The oxidative stability in different samples was assessed in terms of primary and secondary oxidation products as measured by peroxide values and oxidative stability index times, respectively. The quality of the oil samples was also checked through the percentage of free acidity and the phenolic content. Phenols were determined by both spectrophotometric assays (total phenols and o‐diphenols) and HPLC‐DAD/MSD. The antiradical capacity of the phenolic fraction was determined by DPPH and ABTS spectrophotometric tests. These analyses showed that thawing of olives before oil extraction led to a significant loss of oxidative stability and phenols; in contrast, samples obtained from frozen olives that were not thawed before crushing showed qualitative characteristics similar to control samples.     

On the composition of Iranian olive oil

Two samples of virgin olive oil and one sample of hexane-extracted husk oil coming from Iran were examined. The analyses included physical and chemical characteristics, the composition of total fatty acids and fatty acids at the glyceride 2-position by gas liquid chromatography (GLC) of methyl esters, the triglycerides composition calculation according to Vander Wal theory, the separation of the alcoholic fractions (sterols, 4-methylsterols, triterpene alcohols, triterpene dialcohols and aliphatic alcohols) of the unsaponifiable matter by thin layer chromatography (TLC), the quantitation and the composition of these fractions by GLC of TMS derivatives. The results were in line with data from literature for olive oils of different origin, with the exception of: a high content of unsaponifiable matter (1.75 and 1.95% for virgin oils, 5.33% for husk oil); a high amount of sterols for husk oil (562 mg/100 g oil); a low content of SE 30 apparent β-sitosterol for husk oil (91.1%); a low amount of triterpene dialcohols (1 mg/100 g oil) and triterpene alcohols (78 and 91 mg/100 g oil) for virgin oils; a content of cycloartenol (60.2–66.9%) higher than the 24-methylenecycloartanol one (22.8–26.6%; a content of C₂₄ linear saturated alcohol (33.9–38.0%) slightly higher than the C₂₆ alcohol one (29.3–32.8%).     

Machines for olive paste preparation producing quality virgin olive oil

Polyphenolic substances enhance the resistance to oxidation of virgin olive oils, but an excess of polyphenols determines a marked bitter, somewhat tannic taste of the oil, similar to the taste of unripe olives. Tests have been carried out on drupes of different cultivars in industrial productions to evaluate the effect of the machines used to prepare olive pastes on the contents of polyphenols in the oils. Notably greater amounts of polyphenols were found in the oils extracted from hammer-crushed pastes than in the oils extracted from milled pastes. The kneading process which follows, especially if it is long, often reduces the amounts of total polyphenols. Therefore, in order to obtain the best organoleptic and chemical quality in extra virgin olive oils, two systems are suggested for the processing procedures. For olives of certain cultivars (Coratina) and for not-blackened or slightly blackened drupes yielding oils with a very high content of total polyphenols, it is most expedient to use the stone-mill together with a kneader system. But it is more suitable to utilize the hammercrusher together with a kneader system in processing olives (such as the Ogiiarola Salentina or Leccino cultivars) yielding normally “sweet” oils with a low content of total polyphenols.     

Characterisation of virgin olive oils from European olive cultivars introduced in Tunisia

The behaviour of three European olive varieties, Ascolana Tenera, Koroneiki and Picholine, cultivated in the north of Tunisia, was compared to an autochthonous variety, Chétoui. Most of the quality indices and the fatty acid composition showed significant variations between the olive oils. Among the introduced varieties, the Picholine cultivar had the highest value of oleic acid (61%) whereas the Ascolana Tenera cultivar was noteworthy for its lowest content of phenolic compounds (175 mg/kg) and presented the highest level of palmitic acid. The Chétoui variety presented a high content of oleic and linoleic acids. But all samples, both the autochthonous Chétoui and the introduced cultivars, have similar levels of antioxidant compounds, with the exception of phenols. The aroma composition showed significant differences between the oils from the foreign cultivars. The major volatile component was the C‐6 aldehyde fraction whose content varied greatly between the different varieties studied: The E‐2‐hexenal content ranged from 1.6 mg/kg of oil in the Ascolana Tenera variety to >5 mg/kg for the Picholine and Koroneiki cultivars, whereas the Chétoui variety had the lowest levels of volatile compounds, with the exception of the hexanal level which was tenfold higher than in the foreign cultivars. Therefore, our results showed that two of the introduced varieties, Koroneiki and Picholine, showed good adaptation to the Tunisian cultivation conditions. So far, we claim the possibility to develop the successful cultivation of these latter imported varieties in the country.     

Toxic effect of coloured olive compounds on the anaerobic digestion of olive oil mill effluent in UASB-like reactors

Anaerobic sludge digestion of olive oil mill effluent (OOME) in Upflow Anaerobic Sludge Blanket (UASB) reactors was shown to be unstable as a result of both chemical and biological parameters. The study was complicated by the fact that Chemical Oxygen Demand (COD) was removed by growth and maintenance of active biomass and by adsorption in and on the sludge. Coloured compounds caused an inhibition effect on the anaerobic digestion of the wastewater. This inhibition, shown at low COD concentrations of diluted OOME, was due to accumulation of recalcitrant coloured compounds in the sludge, inducing irreversible inhibition of bacterial growth. Partial decolourization of OOME through resin (Duolite XAD 761) treatment reduced the toxic effect.