Mokhtar Guerfel

Chemical composition and oxidative stability of Tunisian monovarietal virgin olive oils with regard to fruit ripening.

The chemical composition of virgin olive oil may be influenced by genotype and different agronomic (i.e. fruit ripeness degree, water supply) and technological factors. This article reports the evaluation of the influence of the olive ripening stage on the quality indices, the major and the minor components and the oxidative stability of the two main monovarietal Tunisian cultivars (cvv. Chétoui and Chemlali) virgin olive oils. Moreover, the olives cv. Chétoui were tested in a rain-fed control and an irrigation regime. The oils sampled at five different ripeness stages were submitted to liquid chromatographic determination (HPLC-DAD/MSD) of their quali-quantitative phenolic and tocopherolic profiles. Moreover, the triacylglycerol and fatty acid compositions, and minor components such as squalene, pigments and their relation with the oil oxidative stability were evaluated. The tested oils showed very good correlation between the oxidative stability and the concentrations of total phenols, practically secoiridoids and α-tocopherol.

Comparative study on volatile compounds from Tunisian and Sicilian monovarietal virgin olive oils

The effects of ripening degree of olives on volatile profile of monovarietal virgin olive oils (VOO) from Tunisian and Sicilian cultivars were investigated. Fruits obtained from Tunisia (Chétoui and Chemlali) and Italy (Nocellara del Belice, Biancolilla and Cerasuola) were picked at three different stages of ripeness and then immediately processed. Moreover, the changes in volatile composition were evaluated in Chétoui variety as a function of the irrigation regime versus the rain-fed control. Using headspace-solid-phase microextraction (HS-SPME) technique coupled to GC-MS and GC-FID, the volatile compounds of the monovarietal virgin olive oils were identified and quantitatively analyzed. The proportions of different classes of volatiles of oils showed significant differences throughout the maturity process. The results suggest that adding to the genetic factor; agronomic conditions affect the volatile formation and therefore the organoleptic properties of VOO.

Changes in lipid composition, water relations and gas exchange in leaves of two young ‘Chemlali’ and ‘Chetoui’ olive trees in response to water stress

The comparative responses of two young olive trees (Olea europaea L. ‘Chemlali’ and ‘Chetoui’) to drought stress were investigated during 1xa0month. Three-month-old own-rooted plants were subjected to two irrigation treatments: WW (well watered plants that were irrigated with fresh water to maintain a soil water content close to field capacity), and WS (water stressed plants by withholding water). Leaf water potential, gas exchange and leaf lipid composition were studied. ‘Chemlali’ was able to maintain higher leaf CO2 assimilation rate and leaf stomatal conductance throughout the drought cycle compared to ‘Chetoui’. Water stress induced a larger decrease in the total lipid content in ‘Chetoui’ than in ‘Chemlali’. Interestingly, the constitution of different lipid classes was highly altered in ‘Chetoui’. Lipid changes in Chemlali, a drought tolerant cultivar, revealed more stability of its cellular membranes to drought stress as compared to the drought susceptible olive cultivar, Chétoui. Furthermore, in comparison to the controls, drought stressed plants showed an increase in the degree of unsaturation of leaf lipids in the two olive cultivars. Moreover, the results observed in Chemlali showed that besides changes in lipids composition this cultivar may have an efficient defence strategy which can be related on antioxidative production against oxidative stress.

The phenolic compounds and compositional quality of Chetoui virgin olive oil: effect of altitude

The differences in the chemical composition of virgin olive oils (VOO) obtained from trees of the Chetoui variety cultivated at different altitudes in Tunisia were evaluated. All samples were harvested using the same controlled procedures and were submitted to a controlled processing in the same laboratory mill. Several analytical parameters such as fatty acid composition, amounts of phenols; o-diphenols and pigments were analyzed. All these parameters showed an important effect on the fatty acids and phenols content of the oils. The total phenol content was positively correlated with the altitude, ranging from 817.33 mg/kg (403 m) to 131.91 mg/kg (10 m). However, the results of the regulated parameters in the potential quality classified all the analyzed oils into the ‘‘extra virgin’’ category. Key words : Orchard elevation, total antioxidant capacity, phenolic compounds, quality index.

Effects of the planting density on virgin olive oil quality of "Chemlali" olive trees (Olea europaea L.).

Here, we report the characterization of virgin olive oil samples obtained from fruits of the main Tunisian olive cultivar (Chemlali) grown in four planting densities (156, 100, 69, and 51 trees ha(-1)). Olive oil samples obtained from fruits of trees grown at 100 trees ha(-1) had a higher content of oleic acid (65.5%), a higher content of chlorophyll and carotenoids, and a higher content in total phenols (1059.08 mg/kg). Interestingly, olives grown at the two highest planting densities yielded more stable oils than olives grown at the two lowest ones. Thus planting density is found to be a key factor for the quality of olive oils in arid regions.

Differences in abscisic acid concentration in roots and leaves of two young Olive (Olea europaea L.) cultivars in response to water deficit

Differences in abscisic acid (ABA) accumulation between two olive cultivars were studied by enzyme-linked immunosorbent assay in roots and leaves, leaf water potential (Ψl), stomatal conductance (gs) as well as photosynthetic rate (A) were also determined in well-watered (WW) and water-stressed (WS) plants of two olive cultivars ‘Chemlali’ and ‘Chetoui’. ‘Chemlali’ was able to maintain higher leaf CO2 assimilation rate and leaf stomatal conductance throughout the drought cycle when compared with ‘Chetoui’. Furthermore, leaf water potential of ‘Chemlali’ decreased in lower extent than in Chetoui in response to water deficit. Interestingly, significant differences in water-stress-induced ABA accumulation were observed between the two olive cultivars and reflect the degree of stress experienced. Chemlali, a drought tolerant cultivar, accumulated lower levels of ABA in their leaves to regulate stomatal control in response to water stress compared to the drought sensitive olive cultivar ‘Chetoui’ which accumulated ABA in large amount.

Olive oil polyphenols extracts inhibit inflammatory markers in J774A.1 murine macrophages and scavenge free radicals

Here we evaluate the olive oil antiradical and anti-inflammatory potential through its polyphenols extracts and examine the influence of olive maturity on olive oil quality properties, polyphenols composition and biological potentials. Samples have been obtained from minor Tunisian olive cultivars (Chemchali, Fouji and Zarrazi) at different maturity indices. Principal quality properties were evaluated and polyphenols analysis was carried out by Folin Ciocalteu reagent and HPLC-UV-MS. Antiradical activity was examined by DPPH and FRAP scavenging assays while J774A.1 murine macrophages were used to evaluate anti-inflammatory potential by analyzing NO production with Griess reagent method and iNOS and COX-2 expression by cytofluorimetric analysis. Our results revealed that quality characteristics, total phenol content, as well as phenolic compound concentrations were significantly affected by the olive maturity levels. On the other hand, the polyphenols extracts showed an interesting radical scavenging capacity and a potential ability to inhibit inflammatory markers at 90% for NO release and 75% for iNOS expression. Thus, our study establishes that olive oil through its polyphenols extracts has a substantial antiradical and anti-inflammatory potential. Likewise a lot of attention should be attributed to olive ripening level in order to decide the optimum harvesting time.

Effects of the planting density on water relations and production of ‘Chemlali’ olive trees (Olea europaea L.)

Water relations are a key factor limiting olive production. In this study, effects of plating density on physiological aspects and productivity of ‘Chemlali’ olive trees were analyzed under rain-fed conditions in four planting densities (156, 100, 69 and 51xa0treesxa0ha−1), in an experimental olive orchard located in the center of Tunisia. Seasonal changes in leaf relative water content (RWC), leaf water potential, stomatal conductance (gs), CO2 assimilation rate and tree production were studied. Accompanying the changes in leaf water status, all the monitored trees reduced leaf stomatal conductance (gs) and photosynthetic rate (A) throughout the summer drought, mirroring the increase in soil moisture deficit and vapor pressure deficit. However, the decrease in gas exchange was much more pronounced in high planting densities than in low ones. Our results confirm that the increase of tree-to-tree water competition with planting density was significant in the dry climate of Tunisia. Thus, planting density is critical when planting new olive orchards in arid regions.