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Extra virgin olive oil (EVOO) samples, of five Greek olive varieties, were stored in dark glass bottles (headspace 0.5%) in a basement without central heating for 24 months. Quantitative variations of the phenolic compounds and their degradation products were monitored over time. The differences observed in the initial total phenolic compounds concentration (ranging between 250.77 and 925.75 mg/kg) were attributed to extraction system, olive variety, and maturity stage. Even after 24 months, the degree of reduction in total phenolic compounds did not exceed 31%. The reduction was more pronounced in dialdehydic forms of oleuropein and ligstroside aglycones (DAFOA and DAFLA), indicating a more active participation in the hydrolysis and oxidation processes of the more polar secoiridoids. The initial total phenolic content was the main factor correlated to the degradation rate of the phenolic compounds. The decrease in secoiridoid derivatives, gave rise to hydroxytyrosol and tyrosol content and to the formation of four oxidized products., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Emulsion gels are considered as an innovative approach to substitute shortenings and margarine in food formulations, e.g., bakery products. Cereal β-glucans are fiber-type constituents, well-known for their human health promoting effects, but also as effective viscosifiers for stabilization of emulsions and aqueous dispersions of solid particles. Barley emulsion gels (BEGs) were formulated with varying weight proportions of β-glucan-enriched (∼27%) barley flour/olive oil/water (from 13/10/77 to 31/30/39) and their physicochemical properties and microstructure as potential solid fat replacers in food formulations were examined. Changes in physical properties and structure of BEGs were monitored using dynamic rheometry, large deformation mechanical testing, differential scanning calorimetry and confocal microscopy during storage (4 °C for 7 days). The rheological tests showed a typical solid-like character for all BEGs (i.e., G' was greater than G'') without oil exudation. The gel strength of BEGs increased upon storage, whereas the thermal properties were dependent on composition and application of heat treatment during BEGs production. Moreover, the microstructure of BEGs revealed that protein particles are located around the surface of oil droplets in the 13/10/77 gels, while in the 31/30/39 formulation, both oil droplets and proteins were entrapped within a more compact hydrated β-glucan-starchy network matrix. The molecular weight of β-glucans (SEC-HPLC) isolated from BEGs was lower than that of β-glucan isolate obtained from the native barley flour. Overall, the multi-instrumental analytical approach employed herein was a suitable framework for evaluation of the physical properties of BEGs as potential solid fat substitutes in the production of healthier formulated products. [Display omitted] • Barley flour emulsion gels (BEGs) enriched with β-glucan were prepared at 25 and 60 °C. • The gel strength and elasticity increased with rise of barley flour and olive oil level, and cold storage. • Degradation of β-glucan was higher in BEGs prepared at 25 °C than that of 60 °C. • Starch gelatinization occurred only in BEGs with high water level prepared at 60 °C. • BEGs with various physical properties were made for use as fat substitutes in healthier products. [ABSTRACT FROM AUTHOR]

The present paper reports on the changes in the volatile composition of virgin olive oils (VOO) stored for 18 months. VOO samples of five Greek olive varieties were stored in dark glass bottles (headspace 0.5%) in a basement without central heating. Even after 18 months of storage, the basic quality characteristics of the samples, such as free acidity, K232, K270, and peroxide values, did not exceed the upper limits set by European Community Regulations for VOO. Regarding the lipoxygenase pathway products, responsible for the positive sensory notes, it was shown that their total amount remained stable during the storage period. Even though the physicochemical characteristics did not exceed the upper limits, high rates of formation of volatile oxidation products, which are responsible for the off-flavors, were observed. Among the volatile oxidation products, the highest rates of formation were monitored for heptanal, 2-heptenal, and pentanal followed by hexanal and nonanal. The formation rate of volatile oxidation products was higher in VOO from Lianolia and Asprolia compared to VOO from Koroneiki, Native from Zakynthos and Thiaki varieties. Finally, stepwise linear regression analysis (SLRA) selected linoleic acid and total phenol/ ortho-diphenols ratio as having the maximum correlation with the formation rate of 2-heptenal. Practical applications: This research reports on the changes in the quality characteristics of VOO, stored for 18 months, of the main olive varieties cultivated in the western Greece. Furthermore, it provides information on the changes in volatile composition, which is responsible for positive and negative flavor attributes. Results from this study may contribute to a better understanding of the relationships between minor and/or major components and the autoxidation process. Moreover, results could be useful to VOO packagers and marketers in order to estimate the shelf-life of individual varieties. VOO from Koroneiki, Native from Zakynthos and Thiaki varieties, which are characterized by low linoleic acid contents, can be preserved for a longer period compared to VOO from Lianolia and Asprolia varieties, which are characterized by high linoleic acid contents. During storage of virgin olive oil (VOO) for 18 months, lipoxygenase pathway products, responsible for the positive sensory notes, remained stable. Among the volatile oxidation products, the highest rates of formation were monitored for heptanal, 2-heptenal, and pentanal, followed by hexanal and nonanal. 2-heptenal was correlated with VOO unsaturation and has been suggested as oxidation marker during storage. [ABSTRACT FROM AUTHOR]

Abstract: In this work the effect of standard phenolic compounds such as trolox, phenolic acids (ferulic, gallic, protocatechuic and caffeic acid) and secoiridoids, extracted from virgin olive oil (VOO), on acrylamide formation in an emulsion system was investigated. The emulsion system was heated in an oil bath at different temperatures and for different periods of time. At 105 and 115°C the generated amounts of acrylamide were negligible during the monitoring time. At 125°C addition of standard phenolic compounds reduced acrylamide formation which was more pronounced at initial time of heating (20min) reaching up to 70%. Protocatechuic and gallic acid were more effective than trolox, caffeic and ferulic acid in acrylamide reduction at the final time intervals of heating (30–60min). On the contrary, addition of VOO extract in the emulsion system resulted in a remarkable increase of acrylamide level, which was ascribed to secoiridoids’ structure containing aldehydic groups. [ABSTRACT FROM AUTHOR]

Abstract: In this study the effect of olive oil and oregano phenolic compounds on antioxidant activity (AOA) and acrylamide formation in a model system and fresh potatoes was evaluated. The addition of oregano phenolic extract in the model system resulted in an increase of AOA and in a reduction of acrylamide content, up to 49%, after heating. On the contrary, addition of olive oil extract resulted in AOA reduction and a concentration-dependent effect on acrylamide formation was observed with a reduction up to 15% (p <0.05) followed by an increase up to 48%. The same trend, in acrylamide formation, was observed in fresh potatoes but to a lower extent. Finally, addition of tyrosol, oleuropein and p-hydroxyphenylacetic acid in the model system resulted in acrylamide reduction up to 50%. The discrepancy in acrylamide formation, caused by phenolic compounds, is ascribed to their structure and related to their terminal functional hydroxyl and aldehydic groups. [Copyright &y& Elsevier]

Virgin olive oil is oil with a high biological value, due to its polyphenol content. Virgin olive oils were subjected to heat treatment simulating common domestic processing, including boiling, frying and storage. These processes can affect the phenolic compounds content of oils to a certain degree, depending on each one treatment. Thermal oxidation of oils at 180 °C (frying) caused a significant decrease (p < 0.005) in hydroxytyrosol derivatives (60% reduction after 30 min and 90% reduction after 60 min) and, to a lower degree, in tyrosol derivatives. No changes were observed in the content of lignans (p > 0.005). On the other hand, thermal oxidation of oils at 100 °C (boiling) for 2 h caused a decrease by less than 20% in all classes of phenolic compounds. The reduction of phenolic compounds during storage under environmental conditions was correlated with the peroxide value. When the peroxide value did not exceed the level of 20 meq⋅kg-1, as was recorded for low linoleic acid oils and low oxygen availability at the bottles' headspace, a degree of reduction of approximately 30% in hydroxytyrosol derivatives and 10% in tyrosol derivatives was observed, while lignans remained unchanged. Finally, during both heating and storage under environmental conditions, the evolution of oxidized phenolic compounds was observed. The structures of these oxidized products were confirmed by HPLC-MS. [ABSTRACT FROM AUTHOR]