Nikolaos Nenadis

A DFT Study on the Radical Scavenging Activity of Maritimetin and Related Aurones

The radical scavenging activity of maritimetin and a series of synthetic aurones has been studied by using density functional theory with the B3LYP exchange correlation functional. The computation of various molecular descriptors that could assist the elucidation of hydrogen atom and electron donating ability of the selected compounds was carried out in the gas phase and in the liquid phase (benzene, methanol, water) with the aid of IEF-PCM. For reasons of comparison a series of simple phenols of known activity were also included in the study. The results are discussed with regards to the structure-activity relationship principles of flavonoids and in particular to the capacity of the selected aurones to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH(*)) and superoxide anion (O(2)(-*)) radicals. The O-H bond dissociation enthalpy (BDE) seems to be the most proper parameter to characterize the antiradical properties of the studied compounds. The hydroxylation pattern in ring B defines the order of activity, while the extended conjugation and especially the presence of a catechol moiety in ring A are responsible for the high activity observed experimentally for the selected aurones.

Assessing the response of plant flavonoids to UV radiation: an overview of appropriate techniques

Abstract Flavonoids are a large group of plant secondary metabolites that are present in most plants, and are vital for plant growth, development and protection. Among the many functions of these compounds is their contribution to stress amelioration. The accurate identification and quantification of total or individual flavonoids in plants exposed to stressful conditions (e.g. ultraviolet radiation) is challenging due to their structural diversity. The present review provides the up to date knowledge and highlights trends in plant flavonoid analysis. The review covers all steps from the field to the laboratory, focussing on UV-B effects on flavonoids, and identifying critical issues concerning sample collection, pre-treatment, extraction techniques and quantitative or qualitative analysis. A well-planned sampling and sample prehandling strategy is vital when capturing organ, tissue and developmental-stage dependent changes in flavonoids, as well as the dynamic changes due to time of UV-exposure and diurnal or seasonal parameters. A range of advanced extraction and purification techniques can facilitate the quantitative transfer of flavonoids to solvents. The advantages and disadvantages of analytical methods, including chromogenic assays, liquid and thin-layer chromatography, mass spectrometry, nuclear magnetic resonance detection, and non-destructive in situ fluorescent analysis need to be consciously evaluated in the context of the specific biological question posed. Thus, no one method can be applied to every single study of flavonoid. The message of this review is that researchers will need to carefully consider the biological process that they intend to study, and select an analytical method that optimally matches their specific objectives.

Effect of recovery methods on the oxidative and physical stability of oil body emulsions

Three natural oil body emulsions of a similar fat content (∼5%), but differing in their protein composition were obtained from an aqueous maize germ extract. The first was prepared by concentrating the aqueous oil body extract with ultrafiltration to a fat content of ∼5%. The other two were prepared by initially recovering the oil bodies from the extract by centrifugation, either in the presence of sucrose or by applying isoelectric precipitation at pH 5.0 and then diluting the resulting oil body creams with deionized water. The oxidative and physical stability of the three emulsions, either as they were or after submission to thermal treatment (100°C for 15 min), were studied following storage at 45°C. The emulsions differed both in their oxidative and physical stability, depending on the recovery method that in turn influenced their continuous phase and/or interfacial membrane protein and/or polar antioxidant composition. Ultrafiltration resulted in the most stable emulsion. Mixtures of the natural oil body emulsions with green tea extracts, aiming to serve as a base for functional beverages, were then prepared and studied for their creaming behaviour. The green tea polyphenols seem to interact with the oil bodies leading to intensive dispersion destabilisation which, however, was halted following carrageenan addition at a relatively very low level.

Applicability of PTR-MS in the quality control of saffron

The applicability of the emerging non-destructive technique, proton transfer reaction mass spectrometry (PTR-MS), was explored for the first time in the quality control of saffron. Monitoring of volatile organic compounds (VOCs) was achieved using a minute sample (35 mg). Fresh saffron was stored under selected conditions (25 and 40 °C, aw=0.64) over a five weeks period to produce lower quality material, which was used to prepare mixtures with fresh saffron. Analysis showed that the VOCs fingerprint changed upon storage, and the concentration of initially dominant VOC safranal decreased progressively. Examination of calculated and recorded fingerprints for various admixtures showed that PTR-MS VOCs analysis, in combination with chemometrics, could be used to screen for the presence of lower quality saffron in a commercial product in a few minutes. The technique can be used in a complementary fashion, adding to the battery of advanced analytical techniques available to address the quality and authenticity issues of saffron.

Interactive effects of UV radiation and reduced precipitation on the seasonal leaf phenolic content/composition and the antioxidant activity of naturally growing Arbutus unedo plants

The effects of UV radiation and rainfall reduction on the seasonal leaf phenolic content/composition and antioxidant activity of the Mediterranean shrub Arbutus unedo were studied. Naturally growing plants of A. unedo were submitted to 97% UV-B reduction (UVA), 95% UV-A+UV-B reduction (UV0) or near-ambient UV levels (UVBA) under two precipitation regimes (natural rainfall or 10-30% rainfall reduction). Total phenol, flavonol and flavanol contents, levels of eight phenols and antioxidant activity [DPPH(●) radical scavenging and Cu (II) reducing capacity] were measured in sun-exposed leaves at the end of four consecutive seasons. Results showed a significant seasonal variation in the leaf content of phenols of A. unedo, with the lowest values found in spring and the highest in autumn and/or winter. Leaf ontogenetic development and/or a possible effect of low temperatures in autumn/winter may account for such findings. Regardless of the watering regime and the sampling date, plant exposure to UV-B radiation decreased the total flavanol content of leaves, while it increased the leaf content in quercitrin (the most abundant quercetin derivative identified). By contrast, UV-A radiation increased the leaf content of theogallin, a gallic acid derivative. Other phenolic compounds (two quercetin derivatives, one of them being avicularin, and one kaempferol derivative, juglanin), as well as the antioxidant activity of the leaves, showed different responses to UV radiation depending on the precipitation regime. Surprisingly, reduced rainfall significantly decreased the total amount of quantified quercetin derivatives as well as the DPPH scavenging activity in A. unedo leaves. To conclude, present findings indicate that leaves of A. unedo can be a good source of antioxidants throughout the year, but especially in autumn and winter.

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.

Effect of Cα–Cβ Bond Type on the Radical Scavenging Activity of Hydroxy Stilbenes: Theoretical Insights in the Gas and Liquid Phase

Density functional theory/Beckes three-parameter hybrid functional combined with the Lee-Yang-Parr correlation functional (DFT/B3LYP) was used to examine the radical scavenging potential of resveratrol, piceatannol, and their dehydro/dihydro counterparts. For this reason, the values of molecular descriptors predicting the hydrogen atom transfer (HAT) and the single electron transfer preceding (SET-PT) or following a proton transfer (SPLET) were computed in the gas and liquid (benzene, water) phases. The double bond, resulting in molecular planarity, was predicted to favor the single hydrogen or electron transfer. The triple bond, resulting in a linear backbone, was predicted to decrease the ease of these transfers, whereas the saturation, resulting in loss of planarity, was expected to decrease the activity even more. The impact of saturation was predicted to be detrimental for resveratrol. However, for piceatannol, an enhancement of activity was proposed only under stepwise HAT because allylic hydrogen atoms could be prone for abstraction after the formation of quinone. The predictions (gas, liquid phase) were in agreement with experimental evidence for resveratrol and its derivatives. The lipophilicity, which may affect antioxidant activity in real systems, increased according to partition coefficient (log P) values as follows: dihydrostilbene > stilbene > dehydrostilbene. On the basis of dipole moment values, no clear trend was observed.

6: Isolation, Purification and Encapsulation Techniques for Bioactive Compounds from Agricultural and Food Production Waste

Rice is a staple food in most Asian countries and a source of energy for 30 per cent of the world’s population (Muller-Fischer 2013). For human consumption, rice is usually processed by being milled and polished into white grain. Rice processing typically yields 56-58 per cent milled white rice (head rice), 10-12 per cent broken grain, 18-20 per cent husk and 10-12 per cent bran (Kahlon and Chow 2001). Head rice is the main commercial product, while the remaining categories constitute rice waste or by-products. Straw is also considered rice waste and its yield per ratio to grain is 1:6 (Schiere et al. 2004). Straw and husk are mainly used for non-food purposes, such as animal feed, craft art, chemical industries and amino acids (Matano et al. 2014, Van Soest 2006). Bran contains the majority of functional substances of rice grain and is unstable due to its oil and lipase content (Kahlon and Chow 2001). This paper provides a review of the bioactive compounds in rice waste and their extraction, isolation and utilisation.