Monovarietal extra virgin olive oils. Correlation between thermal properties and chemical composition: heating thermograms

Physical and Thermal Evaluation of Olive Oils from Minor Italian Cultivars

Authentication of extra virgin olive oils is a key strategy for their valorization and a way to preserve olive biodiversity. Physical and thermal analysis have been proposed in this study as fast and green techniques to reach this goal. Thirteen extra virgin olive oils (EVOOs) obtained from minor olive cultivars, harvested at three different ripening stages, in four Italian regions (Abruzzo, Apulia, Sardinia, and Calabria) have been studied. Thermal properties, viscosity and color, as influenced by fatty acid composition and chlorophyll content, have been investigated. The thermal curves of EVOOs, obtained by differential scanning calorimetry, were mostly influenced by the oleic acid content: a direct correlation with the cooling and heating enthalpy and an indirect correlation with the cooling transition range were observed. The minor fatty acids, and particularly arachidic acid, showed an influence, mostly on the heating thermograms. Viscosity and color showed respectively a correlation with fatty acids composition and chlorophyll content, however they didn’t result able to discriminate between the samples. Thanks to the principal component analysis, the most influencing thermal parameters and fatty acids were used to cluster the samples, based on their botanical and geographical origin, resulting instead the harvesting time a less influential variable.

Fatty acids, triacylglycerols, and thermal behaviour of various mango (Mangifera indica L.) kernel fats

Mango processing generates high amounts of unexploited kernels. Lipid profiles and thermal behaviour of kernel fats from seven Mangifera indica L. cultivars originating from Latin America and Thailand were characterised. Total lipid contents ranged between 5.4 and 11.9%. Detailed GC-FID, GC-MS, and HPLC-DAD-ESI-MSⁿ analyses revealed two fatty acids and five triacylglycerols as novel mango kernel constituents. Owing to the prevailing saturated fatty acids and triacylglycerols, 'Maha Chanook' fat had a significantly higher melting point, the highest solid fat indices at all temperatures, and densely packed crystals as shown by DSC and light microscopy, respectively. In contrast, 'Falan' exhibited high proportions of polyunsaturated fatty acids and triacylglycerols with low equivalent carbon numbers (40-46), resulting in lower melting and crystallisation temperatures and a loosened crystal network. 'Keitt' and 'Palmer' fats showed high proportions of triacylglycerols with medium equivalent carbon numbers (44-52). Mango kernels represent a sustainable source for liquid to semi-solid edible fats suitable for numerous potential applications, e.g., in food and cosmetics.

Tunisian Milk Thistle: An Investigation of the Chemical Composition and the Characterization of Its Cold-Pressed Seed Oils

In this study, milk thistle seeds growing in different areas in Tunisia were cold pressed and the extracted oils were examined for their chemical and antioxidant properties. The major fatty acids were linoleic acid (C18:2) (57.0%, 60.0%, and 60.3% for the milk thistle seed oils native to Bizerte, Zaghouan and Sousse, respectively) and oleic acid (C18:1) (15.5%, 21.5%, and 22.4% for the milk thistle seed oils originating from Bizerte, Zaghouan and Sousse, respectively). High performance liquid chromatography (HPLC) analysis showed the richness of the milk thistle seed oils (MTSO) in α-tocopherol. The highest content was recorded for that of the region of Zaghouan (286.22 mg/kg). The total phenolic contents (TPC) of Zaghouan, Bizerte, and Sousse were 1.59, 8.12, and 4.73 Gallic Acid Equivalent (GAE) mg/g, respectively. Three phenolic acids were also identified (vanillic, p-coumaric, and silybine), with a predominance of the vanillic acid. The highest value was recorded for the Zaghouan milk thistle seed oil (83 mg/100 g). Differences in outcomes between regions may be due to climatic differences in areas. Zaghouan's cold-pressed milk thistle seed oil had a better quality than those of Bizerte and Sousse, and can be considered as a valuable source for new multi-purpose products or by-products for industrial, cosmetic, and pharmaceutical utilization.

Thermal and chemical evaluation of naturally auto-oxidised virgin olive oils: a correlation study

BACKGROUND

The nature of the relationship between differential scanning calorimetry thermal properties and the oxidation and hydrolysis compounds formed during a real auto-oxidation process in virgin olive oils has not been evaluated so far, as these samples are difficult to find. In this work, 21 samples of virgin olive oil, stored under ideal conditions since their years of production (production range 1991-2005) to develop the natural auto-oxidation process, were analysed in order to evaluate this relationship.

RESULTS

Oils stored the longest time showed the highest hydrolytic degradation while the others exhibited higher contents of oxidised fatty acids and triacylglycerols, instead. Thermal properties of transitions were differently influenced by degradation compounds with the onset of both the cooling and heating profiles particularly influenced by diacylglycerols and oxidised lipids. Chemical data and thermal properties were correlated by using principal component analysis. Twenty-three variables were selected for the analysis with the first component fully segregating samples into two groups according to the year of storage and the level of hydrolysis and/or oxidation, on the basis of selected thermal properties obtained by cooling and heating transitions.

CONCLUSIONS

These preliminary findings showed that differential scanning calorimetry could be considered an useful tool to evaluate lipid degradation in virgin olive oils, indicating its value as a support to chemical techniques.

Differential scanning calorimetry thermal properties and oxidative stability indices of microwave heated extra virgin olive oils

BACKGROUND

The use of differential scanning calorimetry (DSC) for assessing the deterioration effect of microwave heating on vegetable oils, and on olive oils in particular, has been partially explored in literature. The aim of this work was to evaluate the potential of DSC to discriminate among microwaved extra virgin olive oils (EvOo from different olive cultivar and origin), according to changes on thermal properties (upon cooling and heating) and traditional oxidative stability indices (peroxide, p-anisidine and TOTOX values).

RESULTS

An elevated value of lipid oxidation was reached by the most unsaturated EvOo sample (9.5% of linoleic acid) at 6 min of microwave treatment. Free acidity significantly increased (0.42%) only for the oil sample with the highest water content (874 mg kg(-1) oil) at the longest time of treatment. Crystallisation enthalpies significantly decreased and the major exothermic peak shifted towards lower temperature, leading to enlargement of the transition range in all samples due to the formation of weak and mixed crystals among triacylglycerols and lipid degradation products. On the contrary, thermal properties upon heating appeared to similarly vary among samples.

CONCLUSIONS

The analysis of DSC thermal properties upon cooling seemed to clearly discriminate among different EvOo samples after microwaving. The relation between changes of thermal properties and oxidation parameters should be further studied using additional oxidative stability indices on a larger set of oil samples, due to the complexity of EvOo composition.

Influence of genetic matrix and crop year on chemical and sensory profiles of Italian monovarietal extra-virgin olive oils

BACKGROUND

Commercial virgin olive oils belonging to the cultivars (Bosana, Carolea, Coratina, Frantoio, Itrana, Leccino, Moraiolo, Peranzana, Piantone di Mogliano and Ravece) most represented at the Italian National Review of Monovarietal olive oils (Rassegna Nazionale Italiana degli oli Monovarietali) were considered. The evaluation of the influence of the cultivar and of the crop year as well as their interaction on oil composition were statistically analysed by a complete factorial design by principal components analysis and by linear discriminant analysis.

RESULTS

In fatty acids composition, the effect of the cultivar and crop year and their interaction were highly significant. The statistical analysis showed that the sensory attributes (olive fruity, grassy, fresh almond, artichoke, tomato, aromatic herbs, bitter and pungent) were strongly influenced by the cultivar. The prevalent effect of the cultivar on the sensory profile was also demonstrated by the low or absent level of significance observed in the crop year.

CONCLUSION

The construction of a databank based on a large number of samples, which is available at URL http://www.olimonovarietali.it, has contributed to the reduction of the variable effects involved in the oil production process. Knowledge of the chemical and sensory profiles of the Italian monovarietal olive oils could start a certification process of these oils, thus giving greater guarantees about their origin.

Olive oil adulterated with hazelnut oils: simulation to identify possible risks to allergic consumers

According to European Union Regulation EC 1531/2001, olive oil labelled as "extra-virgin" should be cold-pressed and contain no refined oil or oil from other oleaginous seeds or nuts. Adulteration of extra virgin olive oil (EVOO) with hazelnut oil (HAO) is a serious concern both for oil suppliers and consumers. The high degree of similarity between the two fats complicates the detection of low percentages of HAO in EVOO. Many analytical approaches have been developed in recent years to trace HAO in EVOO, principally based on chromatographic analyses, differential scanning calorimetry or nuclear magnetic resonance. In addition adulteration of EVOO with HAO may introduce hazelnut-derived allergens. The aim of this work was to analyse the protein and allergen content of EVOO intentionally spiked with raw cold-pressed HAO or solvent-extracted HAO. SDS-PAGE analysis confirmed the presence of hazelnut proteins in solvent-extracted HAO with molecular masses ranging 10-60 kDa. In contrast, cold-pressed HAO showed no traces of protein. In spiked EVOO, solvent-extracted HAO was still detectable at a 1% contamination level. Several bands on SDS-PAGE migrated at apparent molecular masses coinciding with known allergens, such as Cor a 1 (approximately 17 kDa), Cor a 2 (approximately 14 kDa), Cor a 8 (approximately 12 kDa), oleosin (approximately 17 kDa) and Cor a 9 (approximately 60 kDa). MALDI-TOF MS analysis confirmed the presence of two oleosin isoforms and of Cor a 9. Immunoblotting demonstrated that an allergic patient with known reactivity to Cor a 1 and Cor a 2 recognized a 17-kDa band in solvent-extracted HAO. In conclusion, we have shown that adulteration of extra virgin olive oil with solvent-extracted hazelnut oil can be traced by simple SDS-PAGE analysis, and that adulteration introduces a potential risk for hazelnut allergic patients.