Exploring the Bioactive Content of Liquid Waste and Byproducts Produced by Two-Phase Olive Mills in Laconia (Greece): Is There a Prospect for Added-Value Applications?

The use of a two-phase decanter (TwPD) for olive-oil extraction produces wastes and byproducts (a small volume of water from oil washing, olive leaves from the defoliator, and a high moisture pomace which can be destoned) that contain valuable bioactive compounds, such as phenolics and/or triterpenic acids. So far, there is no (water) or limited information (leaves and the destoned pomace fraction) on their content of bioactives, especially triterpenic acids. To contribute to the characterization of such streams from cultivars of international interest, in the present study, samples obtained from five mills from the region of Laconia (from one or two harvests) in Greece, where Koroneiki cv dominates, were screened for phenols and/or triterpenic acids. The leaves and pomace were dried at two temperatures (70 °C and/or 140 °C), and the pomace was also destoned before analysis. The liquid wastes contained low amounts of total (TPC) phenols (<140 mg gallic acid/L), hydroxytyrosol (<44 mg/L), and tyrosol (<33 mg/L). The olive leaves varied widely in TPC (12.8-57.4 mg gallic acid/g dry leaf) and oleuropein (0.4-56.8 mg/g dry leaf) but contained an appreciable amount of triterpenic acids, mainly oleanolic acid (~12.5-31 mg/g dry leaf, respectively). A higher drying temperature (140 vs. 70 °C) affected rather positively the TPC/oleuropein content, whereas triterpenic acids were unaffected. The destoned pomace TPC was 15.5-22.0 mg gallic acid/g dw, hydroxytyrosol 3.9-5.6 mg/g dw, and maslinic 5.5-19.3 mg/g dw. Drying at 140 °C preserved better its bioactive phenols, whereas triterpenic acids were not influenced. The present findings indicate that TwPD streams may have a prospect as a source of bioactives for added-value applications. Material handling, including drying conditions, may be critical but only for phenols.

White rice enrichment with phenols upon cooking in olive leaf infusion: a preliminary study

BACKGROUND

White rice is poor in health-promoting phytochemicals; therefore, the production of a phenol-enriched commodity is highly desirable. Recent findings on its enrichment via cooking in plant extracts are promising, yet studies employing aqueous extracts of olive leaves (OLs), containing well-recognized bioactive phenols (e.g. oleuropein) are absent. In addition, little is known about the levels of phenols that are maintained after rice drying and rehydration, an important aspect for the future design of 'ready-to-eat' functional rice.

RESULTS

The examination, for the first time, of white rice adsorption capacity of phenols from OLs upon cooking in infusions containing different levels of phenols, after freeze-drying and rehydration, showed the following: (i) the total phenol content, the antioxidant activity (assessed via 2,2-diphenyl-1-picrylhydrazyl radical and ferric reducing antioxidant power assays), the oleuropein and luteolin-7-O-glucoside levels increased dose dependently; (ii) upon rehydration, the average decrease of total phenol content and antioxidant activity values was significantly lower when an exact volume of water was used compared with an excess (~10% versus 63%). A similar trend was observed for oleuropein (36% versus 83%) and the luteolin-7-O-glucoside (24 versus 82%) levels; (iii) the dried enriched kernels were less bright with a hay-yellow hue (CIELab coordinates).

CONCLUSION

White rice enrichment with biophenols from OLs, a by-product of olive tree cultivation, was successful using a simple approach. Despite leaching upon freeze-drying/rehydration, sufficient amounts were maintained to obtain a functional rice that could serve as an alternative dietary source of OLs phenols to non-traditional olive tree product consumers or those refraining from sodium and fats. © 2023 Society of Chemical Industry.

Improving the functionality of virgin and cold-pressed edible vegetable oils: Oxidative stability, sensory acceptability and safety challenges

In recent years, there has been a growing demand for minimally processed foods that offer health benefits and premium sensory characteristics. This trend has led to increased consumption of virgin (VOs) and cold-pressed (CPOs) oils, which are rich sources of bioactive substances. To meet consumer needs for new oil products conferring multi-functional properties over a longer storage period, the scientific community has been revisiting traditional enrichment practices while exploring novel fortification technologies. In the last four years, the interest has been growing faster; an ascending number of annually published studies are about the addition of different plant materials, agri-food by-products, or wastes (intact or extracts) to VOs and CPOs using traditional or innovative fortification processes. Considering this trend, the present review aims to provide an overview and summarize the key findings from relevant papers that were retrieved from extensively searched databases. Our meta-analysis focuses on exposing the most recent trends regarding the exploitation of VOs and CPOs as substrates, the fortification agents and their form of use, as well as the fortification technologies employed. The review critically discusses possible health claim and labeling issues and highlights some chemical and microbial safety concerns along with authenticity issues and gaps in quality specifications that manufacturers have yet to address. All these aspects are examined from the perspective of developing new oil products with well-balanced techno-, senso- and bio-functional characteristics.

Effects of Enriched-in-Oleuropein Olive Leaf Extract Dietary Supplementation on Egg Quality and Antioxidant Parameters in Laying Hens

The objective of the present study was to evaluate the effects of an olive leaf extract obtained with an up-to-date laboratory method, when supplemented at different levels in laying hens' diets, on egg quality, egg yolk antioxidant parameters, fatty acid content, and liver pathology characteristics. Thus, 96 laying hens of the ISA-Brown breed were allocated to 48 experimental cages with two hens in each cage, resulting in 12 replicates per treatment. Treatments were: T1 (Control: basal diet); T2 (1% olive leaf extract); T3 (2.5% olive leaf extract); T4 (Positive control: 0.1% encapsulated oregano oil). Eggshell weight and thickness were improved in all treatments compared to the control, with T2 being significantly higher till the end of the experiment (p < 0.001). Egg yolk MDA content was lower for the T2 and T4 groups, while total phenol content and Haugh units were greater in the T2. The most improved fatty acid profile was the one of T3 yolks. The α-tocopherol yolk content was higher in all groups compared to T1. No effect was observed on cholesterol content at any treatment. Based on the findings, it can be inferred that the inclusion of olive leaf extract at a concentration of 1% in the diet leads to enhancements in specific egg quality attributes, accompanied by an augmentation of the antioxidant capacity.

Effects of Dietary Supplementation of a Resin-Purified Aqueous-Isopropanol Olive Leaf Extract on Meat and Liver Antioxidant Parameters in Broilers

Olive leaves are byproducts οf the agro-industrial sector and are rich in bioactive compounds with antioxidant properties. They could be supplemented in poultry diets powdered or less frequently as extracts to improve performance, health and product quality. The objective of this study was to investigate the possible beneficial effects of an aqueous isopropanol olive leaf extract-purified through filtration (250-25 µm) and a resin (XAD-4)-when supplemented in broiler chickens' diets, on meat quality parameters, focusing mainly on antioxidant parameters as there is limited published information. For this purpose, four-hundred-and-eighty-day-old broilers were randomly assigned to four dietary treatments: T1 (control: basal diet); T2 (1% olive leaf extract); T3 (2.5% olive leaf extract); T4 (positive control: 0.1% encapsulated oregano oil commercially used as feed additive). At the end of the experimental period (day 42), the birds were slaughtered, and samples from breast, thigh meat and liver were collected for antioxidant parameters evaluation. On day 1, after slaughter, in thigh meat, Malondialdehyde (MDA) was lower in T2 compared to T3, and total phenolic content (TPC) was higher in T2 compared to T3 and T4. Total antioxidant capacity (TAC) was increased in T2 and T4 breast meat compared to the control. In liver, T4 treatment resulted in higher TPC. The lack of dose-dependent effect for olive leaf extract may be attributed to the pro-oxidant effects of some bioactive compounds found in olive leaves, such as oleuropein, when supplemented at higher levels. In summary, it can be inferred that the inclusion of 1% olive leaf extract in the feed of broilers has the potential to mitigate oxidation in broiler meat and maybe enhance its quality.

The Contribution of Theoretical Prediction Studies to the Antioxidant Activity Assessment of the Bioactive Secoiridoids Encountered in Olive Tree Products and By-Products

Assessment of the antioxidant activity of different types of natural compounds is a complex research area that encompasses various in vitro tests and in vivo studies. Sophisticated modern analytical tools permit the unambiguous characterization of the compounds present in a matrix. The contemporary researcher, knowing the chemical structure of the compounds present, can carry out quantum chemical calculations that provide important physicochemical information assisting the prediction of antioxidant potential and the mechanism behind the activity of target compounds before further experimentation. The efficiency of calculations is steadily improved due to the rapid evolution of both hardware and software. It is possible, consequently, to study compounds of medium or even larger size, incorporating also models that simulate the liquid phase (solution). This review contributes to the establishment of theoretical calculations as an inherent part of the antioxidant activity assessment process, having as a case study the complex mixtures of olive bioactive secoiridoids (oleuropein, ligstroside, and related compounds). The literature indicates great variability in theoretical approaches and models used so far for only a limited number of this group of phenolic compounds. Proposals are made for standardization of methodology (reference compounds, DFT functional, basis set size, and solvation model) to facilitate comparisons and communication of findings.

On the Role of the Carboxyl Group to the Protective Effect of o-dihydroxybenzoic Acids to Saccharomyces cerevisiae Cells upon Induced Oxidative Stress

In the present work, the role of the carboxyl group of o-dihydroxybenzoic acids (pyrocatechuic, 2,3-diOH-BA and protocatechuic, 3,4-diOH-BA) on the protection against induced oxidative stress in Saccharomyces cerevisiae was examined. Catechol (3,4-diOH-B) was included for comparison. Cell survival, antioxidant enzyme activities, and TBARS level were used to evaluate the efficiency upon the stress induced by H₂O₂ or cumene hydroperoxide. Theoretical calculation of atomic charge values, dipole moment, and a set of indices relevant to the redox properties of the compounds was also carried out in the liquid phase (water). Irrespective of the oxidant used, 2,3-diOH-BA required by far the lowest concentration (3–5 μM) to facilitate cell survival. The two acids did not activate catalase but reduced superoxide dismutase activity (3,4-diOH-BA>2,3-diOH-BA). TBARS assay showed an antioxidant effect only when H₂O₂ was used; equal activity for the two acids and inferior to that of 3,4-diOH B. Overall, theoretical and experimental findings suggest that the 2,3-diOH-BA high activity should be governed by metal chelation. In the case of 3,4-diOH BA, radical scavenging increases, and chelation capacity decreases. The lack of carboxyl moiety (3,4-diOH B) improves to radical scavenging, interaction with lipophilic free radicals, and antioxidant enzymes. The present study adds to our knowledge of the antioxidant mechanism of dietary phenols in biological systems.

Suggestions on the Contribution of Methyl Eugenol and Eugenol to Bay Laurel (Laurus nobilis L.) Essential Oil Preservative Activity through Radical Scavenging

The present study examined the radical scavenging potential of the two benzene derivatives found in the bay laurel essential oil (EO), namely methyl eugenol (MEug) and eugenol (Eug), theoretically and experimentally to make suggestions on their contribution to the EO preservative activity through such a mechanism. Calculation of appropriate molecular indices widely used to characterize chain-breaking antioxidants was carried out in the gas and liquid phases (n-hexane, n-octanol, methanol, water). Experimental evidence was based on the DPPH^• scavenging assay applied to pure compounds and a set of bay laurel EOs chemically characterized with GC-MS/FID. Theoretical calculations suggested that the preservative properties of both compounds could be exerted through a radical scavenging mechanism via hydrogen atom donation. Eug was predicted to be of superior efficiency in line with experimental findings. Pearson correlation and partial least square regression analyses of the EO antioxidant activity values vs. % composition of individual volatiles indicated the positive contribution of both compounds to the radical scavenging activity of bay laurel EOs. Eug, despite its low content in bay laurel EOs, was found to influence the most the radical scavenging activity of the latter.

FoodOmicsGR_RI. A Consortium for Comprehensive Molecular Characterisation of Food Products

The national infrastructure FoodOmicsGR_RI coordinates research efforts from eight Greek Universities and Research Centers in a network aiming to support research and development (R&D) in the agri-food sector. The goals of FoodOmicsGR_RI are the comprehensive in-depth characterization of foods using cutting-edge omics technologies and the support of dietary/nutrition studies. The network combines strong omics expertise with expert field/application scientists (food/nutrition sciences, plant protection/plant growth, animal husbandry, apiculture and 10 other fields). Human resources involve more than 60 staff scientists and more than 30 recruits. State-of-the-art technologies and instrumentation is available for the comprehensive mapping of the food composition and available genetic resources, the assessment of the distinct value of foods, and the effect of nutritional intervention on the metabolic profile of biological samples of consumers and animal models. The consortium has the know-how and expertise that covers the breadth of the Greek agri-food sector. Metabolomics teams have developed and implemented a variety of methods for profiling and quantitative analysis. The implementation plan includes the following research axes: development of a detailed database of Greek food constituents; exploitation of "omics" technologies to assess domestic agricultural biodiversity aiding authenticity-traceability control/certification of geographical/genetic origin; highlighting unique characteristics of Greek products with an emphasis on quality, sustainability and food safety; assessment of diet's effect on health and well-being; creating added value from agri-food waste. FoodOmicsGR_RI develops new tools to evaluate the nutritional value of Greek foods, study the role of traditional foods and Greek functional foods in the prevention of chronic diseases and support health claims of Greek traditional products. FoodOmicsGR_RI provides access to state-of-the-art facilities, unique, well-characterised sample sets, obtained from precision/experimental farming/breeding (milk, honey, meat, olive oil and so forth) along with more than 20 complementary scientific disciplines. FoodOmicsGR_RI is open for collaboration with national and international stakeholders.

Getting inside on virgin olive oil (VOO) photooxidation kinetics through combined generalized 2D correlation analysis and moving window 2D correlation analysis of ATR-FTIR spectra

The generalized two-dimensional correlation spectroscopy (g2D-COR spectroscopy) analysis combined with its extended version moving-window 2D-COR (MW-2D-COR) was performed on a set of kinetic ATR-FTIR spectral data. The former is a mathematical method that is applied to a set of spectra collected for a sample exposed to an external perturbation (e.g. storage time). Virgin olive oils (VOOs) of similar fatty acid composition, chlorophyll, and a-tocopherol content were photooxidized (10,912 Lx, no headspace, 24 h). The proposed approach revealed hidden information under specific ATR-FTIR bands and the order of events was established using appropriate rules. MW-2D-COR analysis displayed the evolution of changes during storage. In this way, the detection of the time interval upon which spectral changes are observed was evidenced. As an overview, MW plots of the analyzed samples revealed three time-zones in which changes tend to maximize, with the first one to reach a peak at ~2.5 h. The area around 2850-2930 cm^-1 including bands assigned to the symmetric and asymmetric stretching vibration of the aliphatic -CH₂- bonds, was the one found to be affected in all VOOs. The time interval upon which spectral changes are first detected in the corresponding area could serve as an index for the commencement of the loss of freshness. Present findings highlight the need to combine the two types of correlation analyses to obtain meaningful information on VOO photooxidation kinetics. Lipid scientists may gain an extra tool in their efforts to understand oxidation phenomena.

Virgin olive oil metabolomics: A review

Metabolomics involvement in the study of foods is steadily growing. Such a rise is a consequence of the increasing demand in the food sector to address challenges regarding the issues of food safety, quality, and authenticity in a more comprehensive way. Virgin olive oil (VOO) is a key product of the Mediterranean diet, with a globalized consumer interest as it may be associated with various nutritional and health benefits. Despite the strict legislation to protect this high added-value agricultural commodity and offer guarantees to consumers and honest producers, there are still analytical issues needing to be further addressed. Thus, this review aims to present the efforts made using targeted and untargeted metabolomics approaches, namely nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry-based techniques (mainly LC/GC-MS) combined with multivariate statistical analysis. Case-studies focusing on geographical/varietal classification and detection of adulteration are discussed with regards to the identification of possible markers. The advantages and limitations of each of the aforementioned techniques applied to VOO analysis are also highlighted.

Toward a Harmonized and Standardized Protocol for the Determination of Total Hydroxytyrosol and Tyrosol Content in Virgin Olive Oil (VOO). The Pros of a Fit for the Purpose Ultra High Performance Liquid Chromatography (UHPLC) Procedure

Τoward a harmonized and standardized procedure for the determination of total hydroxytyrosol and tyrosol content in virgin olive oil (VOO), the pros of a recently published in house validated ultra high performance liquid chromatography (UHPLC) protocol are discussed comparatively with those of other procedures that determine directly or indirectly the compounds hosted under the health claim on “olive oil polyphenols” (EC regulation 432/2012). Authentic VOOs were analyzed with five different liquid chromatographic separation protocols and ¹H-NMR one in five different laboratories with expertise in VOO phenol analysis within three months. Data comparison indicated differences in absolute values. Method comparison using appropriate tools (Passing-Bablok regression and Bland Altman analyses) for all protocols vs. the UHPLC one indicated slight or statistically significant differences. The results were also discussed in terms of cost effectiveness, detection means, standard requirements and ways to calculate the total hydroxytyrosol and tyrosol content. Findings point out that the in-house validated fit for the purpose UHPLC protocol presents certain pros that should be exploited by the interested parties. These are the simplicity of sample preparation, fast elution time that increase the number of samples analyzed per day and integration of well-resolved peaks with the aid of only two commercially available external standards. Importance of correction factors in the calculations is stressed.

Real time monitoring of the combined effect of chlorophyll content and light filtering packaging on virgin olive oil photo-stability using mesh cell-FTIR spectroscopy

The present work aimed at examining the combined effect of chlorophyll content and light filtering packaging material on the photo-stability of virgin olive oil (VOO) via mesh cell-FTIR spectroscopy monitoring. Four different VOOs of Koroneiki cultivar differing in total chlorophyll content (∼12-46 mg/kg) were exposed in parallel to direct visible light (6000 lx, 24 °C, 344 h) and FTIR spectra were recorded periodically with or without applying light protection by an industrial filter used for packaging. Findings suggested that the protective role of light filtering material was more evident in the VOO with the lowest total chlorophyll content. Real time monitoring of VOO by mesh cell-FTIR was found to be a useful tool to follow the combined effect of pro-oxidant chlorophylls and the protective light filtering materials on the photo-oxidation process of VOO employing a minute sample amount.

In House Validated UHPLC Protocol for the Determination of the Total Hydroxytyrosol and Tyrosol Content in Virgin Olive Oil Fit for the Purpose of the Health Claim Introduced by the EC Regulation 432/2012 for "Olive Oil Polyphenols"

An ongoing challenge in olive oil analytics is the development of a reliable procedure that can draw the consensus of all interested parties regarding the quantification of concentrations above the required minimum value of 5 mg of bioactive “olive oil polyphenols” per 20 g of the oil, to fulfill the health claim introduced by the European Commission (EC) Regulation 432/2012. An in-house validated ultra-high performance liquid chromatography (UHPLC) protocol fit for this purpose is proposed. It relies on quantification of the total hydroxytyrsol (Htyr) and tyrosol (Tyr) content in the virgin olive oil (VOO) polar fraction (PF) before and after acidic hydrolysis of their bound forms. PF extraction and hydrolysis conditions were as previously reported. The chromatographic run lasts ~1/3 of the time needed under high performance liquid chromatography (HPLC) conditions, this was also examined. Eluent consumption for the same piece of information was 6-fold less. Apart from being cost effective, a larger number of samples can be analyzed daily with less environmental impact. Two external curves, detection at 280 nm and correction factors for molecular weight difference are proposed. The method, which is fit for purpose, is selective, robust with satisfactory precision (percentage relative standard deviation (%RSD) values < 11%) and recoveries higher than 87.6% for the target analytes (Htyr, Tyr). Standard operational procedures are easy to apply in the olive oil sector.

Functional Teas from the Leaves of Arbutus unedo: Phenolic Content, Antioxidant Activity, and Detection of Efficient Radical Scavengers

The phenolic content/composition and antioxidant activity of hot/cold infusion and decoction from the leaves of Arbutus unedo were studied for the first time. 1,1-diphenyl-2-picrylhydrazyl (DPPH^●), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radical cation (ABTS^●+), crocin-bleaching, copper-reducing, and liposome accelerated oxidation assays were used for the evaluation of the activity in vitro. In vivo, the extracts were examined for their ability to protect S. cerevisiae cells from H₂O₂ induced oxidative stress. An on-line high-performance liquid chromatography-DPPH^● assay was applied to identify potent radical scavengers and comment on their contribution to the total activity. The addition of leaves to boiling water (decoction) was the most appropriate practice to apply since the highest phenol intake (220.2 mg gallic acid/cup served) was obtained. Additionally, its antioxidant activity was equal or superior to that of the other extracts. Flavonols (~51-61 mg/g dry extract) were the main phenols in all the extracts, with quercitrin accounting for ~20% of the total phenol amount. The on-line DPPH^● method verified the high potency of the decoction and indicated as the most active radical scavengers, two galloylquinic acid derivatives and myricitrin, accounting for ~28-45% and ~11-13% of the total scavenging, respectively. Present data may contribute to the future exploitation of A. unedo leaves by the food industry for health-promoting herbal tea preparations and dietary supplements.

Addressing analytical requirements to support health claims on "olive oil polyphenols" (EC Regulation 432/2012)

A health claim on "olive oil polyphenols", namely, hydroxytyrosol and its derivatives, was recently approved by EC Regulation 432/2012. As no official method exists so far for the complete separation of all forms of hydroxytyrosol and tyrosol present in the oil, it is of utmost importance to find a simple, reproducible, and undisputable protocol to protect consumers and avoid unfair competition. In this study two hydrolysis protocols for the complex forms either in the polar fraction of the oil (protocol 1) or directly in the oil (protocol 2) were comparatively applied to a series of extra virgin olive oils. Protocol 1 gave at least 50% higher levels of total hydroxytyrosol and tyrosol. Nevertheless, the minimum amount of 5 mg/20 g oil of phenols was fulfilled only when suitable correction factors were introduced in the calculations to account for the differences in the mass between simple and complex phenols. Changes in the terminology used in the health claim are also proposed.

Evaluation of potential genotoxicity of virgin olive oil (VOO) using the drosophila wing-spot test

Edible and nonedible grades of virgin olive oil (VOO), differing in quality characteristics, were evaluated for potential genotoxicity in the Drosophila somatic mutation and recombination test (SMART) before and after heating at high temperatures. Drosophila larvae were fed on medium containing 6 and 12% v/v of each of the examined oils. Edible VOOs did not exhibit any mutagenic or recombination activity even after thermal treatment. Lower grade VOO gave negative results at the concentration of 6% and inconclusive ones at 12%. However, after its thermal treatment, a statistically significant increase of large single spots was observed, giving a positive result for this spot category at both concentrations. Evaluation of the possible contribution of olive phenolic compounds to the nongenotoxic effects observed was carried out using a polar olive leaf extract and pure oleuropein. No significant increase in the frequency of any category of mutant spots was recorded for leaf extract (0.8-12 mg of total polar phenols/dose) or pure oleuropein (0.8-8 mg/dose). These results are expected to contribute to the ongoing interest in the inherent properties of VOO as part of the everyday diet.

Further examination of antiradical properties of Crocus sativus stigmas extract rich in crocins

Data for antiradical properties of saffron extract and its bioactive constituents (crocins, crocetin) are limited and poorly discussed in comparison with those of extracts containing potent scavengers. Further examination was sought using the Folin-Ciocalteu (F-C) reagent and various free radical species produced in cell-free or cell model systems. Oregano and turmeric methanol extracts, rich in well established scavengers, and also crocetin, rosmarinic acid, and curcumin, representing the major types of constituents in the three studied extracts, were used as "reference". On the same weight basis, saffron extract activity was found to be rather negligible in all cell-free systems with regard to that found for reference ones. On the contrary, in the human monocyte system, saffron extracts or free crocetin were found to reduce ROS production as effectively as the phenolic antioxidants. Our findings point out that saffron extracts exhibit a remarkable intracellular antioxidant activity that cannot be revealed using assays repeatedly applied to the evaluation of phenolic-type antioxidants.

Use of reference compounds in antioxidant activity assessment

The choice of reference compounds is examined as a "critical control point" of antioxidant activity assessment. Gallic, caffeic, sinapic, uric, and ascorbic acids, isoeugenol, and Trolox were tested using different redox (FRAP, Folin-Ciocalteu) and radical scavenging (DPPH*, ABTS*+, CBA, ORAC) assays. The ability to chelate transition metals was assessed to support some of the findings. Analytes were also tested in liposomes. On the basis of the findings, we do not recommend uric acid (due to solubility constrains) and ascorbic acid (due to fast degradation kinetics) as references. The behavior of the rest of the compounds could not always be attributed to typical structural characteristics. Selection of suitable reference compounds for in vitro antioxidant activity assays is not an easy task to achieve. The choice of reference compounds has to remain at the convenience of the researchers, with regard to the aim of the study.

Radical scavenging potential of phenolic compounds encountered in O. europaea products as indicated by calculation of bond dissociation enthalpy and ionization potential values

The radical scavenging potential of phenolic compounds occurring in Olea europaea and of recently identified hydroxytyrosol metabolites was evaluated by means of quantum chemical calculations. The bond dissociation enthalpy (BDE) of phenolic hydroxyl groups and the ionization potential (IP) were calculated as descriptors to predict the H-atom-donating and electron-donating abilities of antioxidants, respectively. Catechol derivatives had the lowest BDE values (77.7-80.1 kcal/mol) whereas the lignans, pinoresinol and 1-acetoxypinoresinol, and other monophenols had much higher BDE values (85.1-88.0 kcal/mol), which suggested a lower potential for radical scavenging. Side chain characteristics were not found to affect the size of BDE values although differences in lipophilicity (on the basis of calculated Log P values) indicate variability in the activity in real systems. Conclusions for the antioxidant potential could not be drawn based on the IP values. Lack of experimental data for most of the studied compounds due to oxidative instability and difficulties in synthesis or isolation supports the usefulness of a computational approach for those interested in the antioxidant potential of phenolics encountered in O. europaea products.

Estimation of scavenging activity of phenolic compounds using the ABTS(*+) assay

Observations on the applicability of the ABTS(*+) assay to define structure-activity relationships (SARs) among phenols (AH) were based on experimental data and theoretical calculations. All AH examined (hydroxycinnamic derivatives, simple polyphenols, polyhydroxybenzoates, and flavonoids) were found to be active toward ABTS(*+). Moreover, known weak radical scavengers (i.e., coumaric and isoferulic acids) were found to be efficient or comparatively active to caffeic or rosmarinic acids in contradiction to the AH classification based on 1,1-diphenyl-2-picrylhydrazyl (DPPH) data or the bond dissociation enthalpy values. This behavior was observed both in ethanol and in buffered (pH 7.4) environment. Resorcinol and phloroglucin were found to be more active than catechol and hydroquinone, whereas, among polyhydroxybenzoates, 2,4-dihydroxybenzoic acid was the least active, in line with the DPPH and theoretical data. Therefore, it can be argued that the ABTS(*+) assay may give an indication for the presence of antioxidants in a certain system but SARs cannot be readily inferred.

Structure-antioxidant activity relationship of ferulic acid derivatives: effect of carbon side chain characteristic groups

Differences in the antioxidant activity of some biosynthetically related ferulic acid derivatives induced by the presence of characteristic groups (-COOH, -CHO, -CH(2)OH, -CH(3), and -COOC(2)H(5)) at the end of their carbon side chain were investigated using both experimental and computational methods. The relative order of the scavenging activity toward the DPPH radical derived from kinetic studies was isoeugenol approximately coniferyl alcohol >> ferulic acid approximately coniferyl aldehyde approximately ethyl ferulate. In bulk oil autoxidation (45 degrees C) the same order of activity was obtained. In the o/w emulsion autoxidation, lipophilicity of the phenols was the determining factor because the least polar compounds bearing -CH(3) and -COOC(2)H(5) were the most effective ones. The order of activity based on the O-H bond dissociation enthalpy (BDE) and ionization potential (IP) values, calculated by the density functional theory (DFT) method, was in accordance with the experimental radical scavenging order and with the electron-donating/withdrawing properties of the characteristic groups. Other molecular descriptors could not complement the experimental findings.

Antioxidant activities and phenolic composition of extracts from Greek oregano, Greek sage, and summer savory

Oregano vulgare L. ssp. hirtum (Greek oregano), Salvia fruticosa (Greek sage), and Satureja hortensis (summer savory) were examined as potential sources of phenolic antioxidant compounds. The antioxidant capacities (antiradical activity by DPPH* test, phosphatidylcholine liposome oxidation, Rancimat test) and total phenol content were determined in the ethanol and acetone extracts of the dried material obtained from the botanically characterized plants. The ground material was also tested by the Rancimat test for its effect on the stability of sunflower oil. The data indicated that ground material and both ethanol and acetone extracts had antioxidant activity. Chromatographic (TLC, RP-HPLC) and NMR procedures were employed to cross-validate the presence of antioxidants in ethanol and acetone extracts. The major component of all ethanol extracts was rosmarinic acid as determined by RP-HPLC and NMR. Chromatography indicated the presence of other phenolic antioxidants, mainly found in the acetone extracts. The presence of the flavones luteolin and apigenin and the flavonol quercetin was confirmed in the majority of the extracts by the use of a novel (1)H NMR procedure, which is based on the strongly deshielded OH protons in the region of 12-13 ppm without previous chromatographic separation. This deshielding may be attributed to the strong intramolecular six-membered ring hydrogen bond of the OH(5)...CO(4) moiety.