Characterization of a 13-lipoxygenase from virgin olive oil and oil bodies of olive endosperms

Olive oil is one of the oldest known vegetable oils, and it is almost unique in that it can be consumed without any refining treatment. One of its most important quality problems is oxidative rancidity due to the oxygenation of polyenoic fatty acids and formation of compounds that derive from these fatty acid hydroperoxides. Beside autoxidation, lipoxygenases (LOXs) were suggested to be involved in this process. Here we show, that approximately 1.6% of all linoleic acid (LA) molecules within olive oil samples had been converted into LOX-derived (13S,9Z,11E)-13-hydroperoxy-9,11-octadecadienoic acid (13-HPODE) as determined by ¹H NMR- and HPLC analysis. LOX activity tests indicated the occurrence of an active 13-LOX exhibiting a pH optimum between pH 5.5 and 6.0. Furthermore, this enzyme preferentially metabolized free fatty acids. In order to elucidate the origin of this LOX, we analyzed olive endosperms for LOX forms. Chromatography of total protein extracts of the tissue showed LOX activity almost exclusively associated with a high molecular mass fraction. Light microscopic inspection, as well as the calculated phosphate, neutral lipid, and protein content of this fraction, suggested that this fraction may contain oil bodies and that LOX activity was associated with their membrane. This LOX activity had a pH optimum of 6.0. Activity assays at various temperatures indicated a significant catalytic efficiency of the enzyme up to 55°C. HPLC analysis of LA oxygenation products within the lipid fraction and of activity tests of isolated oil bodies showed that the LOX present in mature olive endosperm oil bodies was, as the enzyme from olive oil, a linoleate 13-LOX preferentially active on free LA. We suggest, that this oil body LOX from olive endosperm, is the one detected originally in olive oil and may survive at least in part olive oil production.     

A new decanter generation leads to innovation in olive oil processing

Looking at the olive oil production, the final extraction phase from the paste affects the yield and the quality of the oil more than other processing steps. Several strategies are therefore applied today to increase the process outcome already before extraction at the malaxation stage. Technical innovation is particularly realized in adopting olive oil decanters that enable real‐time adjustments of working parameters in function of the different composition of the raw materials, improving the yield of the process and avoiding a significant economic loss for the sector. In the paper of Caponio, Summo, Paradiso and Pasqualone published in this issue of the European Journal of Lipid Science and Technology [1626–1633], the performance of the so‐called “third generation” decanter is presented showing the impact of its application on the chemical, nutritional, olfactory and sensorial quality in the sector of olive oil processing. The significance of the achieved results is underlined in the following commentary.     

Enzymatic interesterification of olive oil with fully hydrogenated palm oil: Characterization of fats

Seven different reaction products were prepared via enzymatic interesterification of extra‐virgin olive oil (EVOO) and fully hydrogenated palm oil (FHPO), by varying the initial weight ratio of EVOO to FHPO from 80 : 20 to 20 : 80. The chemical, physical and functional properties of both the semi‐solid reaction products and the corresponding physical blends of the precursor starting materials were characterized. Fats prepared using large proportions of FHPO contained high levels of TAG species containing only saturated fatty acid residues. By contrast, high levels of TAG species containing both saturated and unsaturated fatty acid residues were found in fat products obtained with the lowest proportions of FHPO. Independently of the initial weight ratio of EVOO to FHPO, the interesterified products were characterized by a higher molar ratio of unsaturated to saturated fatty acid residues at the sn‐2 position, were softer over a wide temperature range, exhibited lower oxidative stabilities and were completely melted at lower temperatures than the corresponding physical blends. Potential applications of the reaction products range from margarines (highest weight ratios of EVOO to FHPO) to frying fats (lowest weight ratios of EVOO to FHPO).     

Characterization of virgin olive oil from Southern Tunisia

Fruits from three Tunisian cultivars of Olea europea L. grown in the southeast of Tunisia were harvested at the maturity stage of ripeness and immediately processed with a laboratory mill. There are as yet no data on the chemical composition of virgin olive oils from the southeast of Tunisia, an area characterized by an arid condition of growth for olive trees. Our results showed significant differences in the analytical parameters examined for the three cultivars such as fatty acid composition, total phenols and o‐diphenols, and the content of chlorophylls and carotenoids, confirming the importance of genetic factors in the chemical characteristics of the oil. Headspace solid‐phase microextraction (HS‐SPME) was applied to the analysis of volatile compounds of virgin olive oils. Forty‐eight compounds were isolated and characterized by GC‐RI and GC‐MS, representing 94.1–98.1% of the total amount. (E)‐Hex‐2‐enal, the main compound extracted by SPME, characterized the olive oil headspace for all samples. So, it was clearly shown that there were qualitative and quantitative differences in the proportion of volatile constituents from oils of the various cultivars.     

Improving olive oil quality using CO2 evolved from olive pastes during processing

The effect of blanketing with CO₂, naturally evolved during malaxation of olive pastes, on the quality of virgin olive oil was investigated at lab‐scale. The O₂ depletion was monitored along with CO₂ emission to confirm the previously hypothesized accelerated respiration. Malaxation experiments were conducted for 180 min both in sealed (SC) and in the traditional open‐to‐air conditions to ascertain whether the oil quality was affected by O₂ concentration as afforded by CO₂ blanketing. The quality of olive oils obtained at different time intervals was monitored by total acidity, peroxide value (PV), specific extinction coefficients K₂₃₂ and K₂₇₀, total chlorophyll and total hydrophilic phenols, and HPLC hydrophilic phenols profile. A rapid decrease in oxygen concentration and a simultaneous increase in CO₂ concentration were recorded, confirming the accelerated respiration. The oil produced in SC showed a lower PV and K₂₃₂ coefficient and a higher chlorophyll (10–17 mg/kg) and hydrophilic phenols (110 mg/kg) concentration. No differences in total acidity and K₂₇₀ coefficient were observed. The hydrophilic phenols profile indicated that, at least for the Frantoio cultivar and an advanced ripeness state, the maximal extraction is generally achieved already after 20 min. Most of the individual hydrophilic phenols have higher concentrations (up to 50%) in SC.     

Characterization of olive oil classes using a Chemsensor and pattern recognition techniques

Classification is an important component of food quality assurance, as methods to guarantee authenticity of food products are widely demanded by food producers, processors, consumers, and regulatory bodies. The objective of this work was to develop a rapid classification method in order to discriminate virgin olive oil, olive oil, and „orujo” olive oil, the prices of which differ dramatically in the market on a ccount of the high quality level of the former. For these purposes, new ChemSensor equipment that combines a headspace autosampler with a mass-selective detector and Pirouette data evaluation software was used. To take into account the large number of samples analyzed (50 samples repeated 10 times), as well as the wide interval of m/z ratios scanned (41–170), chemometric approaches were necessary. Cluster analysis, principal component analysis, K-nearest neighbors, and soft independent modeling of class analogy (SIMCA) were applied to model the different oil classes. The results indicated good classification and prediction abilities, with SIMCA affording the best results (viz. 97% specificity).     

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.     

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.     

Thin layer drying kinetics of by-products from olive oil processing

The thin-layer behavior of by-products from olive oil production was determined in a solar dryer in passive and active operation modes for a temperature range of 20-50 °C. The increase in the air temperature reduced the drying time of olive pomace, sludge and olive mill wastewater. Moisture ratio was analyzed to obtain effective diffusivity values, varying in the oil mill by-products from 9.136 × 10(-11) to 1.406 × 10(-9) m(2)/s in forced convection (m(a) = 0.22 kg/s), and from 9.296 × 10(-11) to 6.277 × 10(-10) m(2)/s in natural convection (m(a) = 0.042 kg/s). Diffusivity values at each temperature were obtained using the Fick's diffusion model and, regardless of the convection, they increased with the air temperature. The temperature dependence on the effective diffusivity was determined by an Arrhenius type relationship. The activation energies were found to be 38.64 kJ/mol, 30.44 kJ/mol and 47.64 kJ/mol for the olive pomace, the sludge and the olive mill wastewater in active mode, respectively, and 91.35 kJ/mol, 14.04 kJ/mol and 77.15 kJ/mol in natural mode, in that order.     

Quality of virgin olive oil extracted with the new centrifugation system using a two-phases decanter

Research has been carried out to determine the quality of oil extracted with the new centrifugation system adopting a two-phases decanter. The quality has also been compared with that of oil extracted with the current centrifugation system using a three-phases decanter. Tests were performed in an industrial oil mill, that was equipped with two- and three-phases decanters. Results obtained show that oil extracted with the two different decanters do not differ in free fatty acids, peroxide value, and ultraviolet absorption. On the contrary, the polyphenol and o-diphenol contents are higher in oils obtained with the new centrifugation system than those of oils from the current centrifugation system. For this reason oils obtained with the new extraction system show an increased resistance to autoxidation.     

Understanding degradation of phenolic compounds during olive oil processing by inhibitor addition

The aim of this work was to study, under different conditions, degradation of secoiridoids during extraction of extra virgin olive oil by following the effect of ascorbic and citric acid addition. Their effect was evaluated on oil obtained from both damaged olives and undamaged fresh olives. Addition of enzyme inhibitors to damaged olives during olive milling allowed us to obtain oil with a higher phenolic compound content. Conversely, addition of the same inhibitors to undamaged fresh olives, during oil milling, resulted in no significant improvement in the phenolic compound content of oil. A high presence of PPO was thus indirectly confirmed, as damaged olives were only found to be sensitive to action of inhibitors. Ascorbic acid was found to be more effective than citric acid in preserving phenolic compounds of oil. Trials on undamaged fresh olives confirmed occurrence of hydrolytic transformation phenomena for secoiridoids during extra virgin olive oil production process. In particular, the quantitatively most representative component for Frantoio cultivar was found to be 3,4‐DHPEA‐EDA. This compound may be considered a direct marker for the degree of transformation of secoiridoids during production process. Practical applications: The processing of undamaged olives resulted in the extraction of extra virgin olive oil with a higher phenol content. It could be indirectly inferred that a reduced activity of PPO caused a low secoiridoid degradation both before and after malaxation. Lightly scratched, overripe olives could be used in those markets where the addition of oxidation‐inhibiting substances is allowed. Using inhibitors can be suggested for olive washing step.     

Use of a fluoroelastomer processing aid with non-olefin polymers

A die coated with fluoroelastomer (FE) has been used in the extrusion of thermoplastics other than conventional polyolefins, and including chlorinated polyethylene, polystyrene, polycarbonate, and an ionomer. Inverse gas chromatography was the source of acid/base interactions between FE and each of these matrix polymers. FE was found to be effective in reducing the apparent melt viscosity when the host polymer was acidic, or non-interactive. With strongly interactive, basic polymers the effectiveness of FE flow modifier was anulled. These polymers may be considered as effective purging agents for extrusion equipment containing FE residues.     

A new processing aid for the extrusion of polyolefins

The influence of a new processing additive (a composition of fine particles of boron nitride) on the rheology and processability of molten polymers is studied. The equipment used includes both an Instron capillary rheometer with special annular dies (Nokia Maillefer wire coating crosshead) attached to the rheometer and a parallelplate rheometer. Two metallocene polyethylenes with several types of boron nitride powders varying in particle size distribution are tested at various concentration levels. The powder having the finest particle size was found to have the greatest influence in the processing of polyolefins using crosshead dies and tips. As a result, its use eliminates surface melt fracture and postpones the critical shear rate for the onset of gross melt fracture to significantly higher values depending on the additive concentration. The performance of the boron nitride in eliminating melt fracture is compared with that of a typical fluoroelastomer. It is shown that boron nitride is a superior processing aid.     

Characterization of new types of mannosylerythritol lipids as biosurfactants produced from soybean oil by a basidiomycetous yeast, Pseudozyma shanxiensis

Mannosylerythritol lipids (MELs) are glycolipid biosurfactants produced by the yeast strains of the genus Pseudozyma. These show not only the excellent surface-active properties but also versatile biochemical actions. In course of MEL production from soybean oil by P. shanxiensis, new extracellular glycolipids (more hydrophilic than the previously reported MELs) were found in the culture medium. As a result of the structural characterization, the glycolipids were identified as a mixture of 4-O-[(2', 4'-di-O-acetyl-3'-O-alka(e)noyl)-beta-D-mannopyranosyl]-D-erythritol and 4-O-[(4'-O-acetyl-3'-O-alka(e)noyl-2'-O-butanoyl)-beta-D-mannopyranosyl]-D-erythritol. Interestingly, the new MELs possessed a much shorter chain (C(2) or C(4)) at the C-2' position of the mannose moiety compared to the MELs hitherto reported, which mainly possess a medium-chain acid (C(10)) at the position. They would thus show higher hydrophilicity and/or water-solubility, and expand the development of the environmentally advanced yeast biosurfactants.     

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.