Special Issue "Phenolics and Polyphenolics"

Guest Editor
Prof. Dr. Liselotte Krenn
Institute of Pharmacognosy, PharmaCenter Vienna, University of Vienna, Althanstr. 14, A-1090 Vienna, Austria
E-Mail:
Interests: flavonoids; anthraquinones; isolation and structure elucidation; analysis (LC-DAD; LC-MS); in vitro assays (antioxidant properties; acetylcholinesterase inhibition; histonedeacetylase modulation)

Editorial Advisor
Prof. Dr. Paula Andrade
REQUIMTE/Serviço de Farmacognosia, Faculdade de Farmácia, Universidade do Porto, R. Aníbal Cunha, 164, 4050-047 Porto
E-Mail:

Editorial Advisor
Prof. Dr. José Alberto Pereira
CIMO/Escola Superior Agrária, Instituto Politécnico de Bragança, Campus Sta Apolónia, Apartado 1 172, 5301-855 Bragança, Portugal
E-Mail:
Interests: bioactive phytochemicals; phenolic compounds; antioxidant and antimicrobial activities; effect of agricultural practices on vegetable composition and quality; olives and olive oil chemistry

Dear Colleagues,

This special issue of the International Journal of Molecular Science is dedicated to phenolics and polyphenols. Polyphenols are among the most abundant substances produced in plant kingdom comprising numerous diverse classes of secondary metabolites such as phenolic acids, flavonoids, tannins, coumarins, stilbenes, lignans.

During the recent decades such compounds have gained an enormous interest in research. Their diverse functions in plants, biosynthesis, biological properties etc. are studied in detail. Besides that the health effects of phenolics and polyphenols are investigated intensively. Numerous representatives of these compounds are e.g. assumed to contribute by different modes of action to the prevention of chronic diseases associated with oxidative stress such as cancer or cardiovascular diseases. This has stimulated investigations not only on the activites but also on the concentrations of such compounds in all kinds of food and medicinal plants as well as on their intake, absorption, bioavailability and metabolism. Recommendations to ingest of high amounts for preventional purposes have raised the question of toxicity and led to respective studies.

For the use of extracts rich in polyphenols in herbal medicinal products and food supplements, the development of appropriate analytical methods and optimum formulations are important research fields as well.

Nevertheless, there are still apparent gaps in the knowledge concerning phenolics and polyphenols. Besides many others e.g. the full understanding of their role and function in plants at the molecular level or interactions in the environment need further investigation. Thus, this special issue shall help to fill some of the gaps in all above mentioned fields of research.

Liselotte Krenn
Guest Editor

Submission

All papers should be submitted to ijms@mdpi.org. To be published continuously until the deadline and papers will be listed together at the special issue website.

Submitted papers should not have been published previously, nor be under consideration for publication elsewhere. All papers are refereed through a peer-review process. A guide for authors is available on the Instructions for Authors page. The International Journal of Molecular Sciences is an international peer-reviewed monthly journal published by Molecular Diversity Preservation International.

Open Access publication fees are 800 CHF per paper. English correction fees and/or formatting fees (250 CHF) will be added in certain cases (1050 CHF per paper for those papers that require extensive additional formatting and/or English corrections).

Also see a list of papers published on the same topic in Molecules in 2007.

• phenolics
• polyphenolics and molecular sciences

Feature Papers

Type of Paper: Review
Title: Methylation of Dietary Flavones Increases Their Metabolic Stability and Chemopreventive Effects
Authors: Thomas Walle
Affiliations: Department of Cell and Molecular Pharmacology and Experimental Therapeutics, Medical University of South Carolina, 173 Ashley Avenue, Charleston, SC 29425, USA; E-mail: wallet@musc.edu
Abstract: Dietary flavones have been shown to have promising chemopreventive properties, in particular with regard to cancer. However, problems with too low oral bioavailability and sometimes unacceptable toxicity have made them questionable for use as protective additives to normal diets. Research in pharmacognosy has revealed many flavone derivatives, some of which may have superior chemopreventive properties, e.g. methylated flavones, or methoxyflavones. First, recent studies have shown that methylation of free phenolic hydroxyl groups leads to derivatives lacking the propensity for undergoing conjugation to either glucuronic acid or sulfate conjugates, resulting in much increased metabolic stability. Such methylation also leads to greatly improved transport through biological membranes, such as in intestinal absorption. Second, recent studies also indicate that methylation results in derivatives with increasing potency to kill cancer cells, although these effects may be cell-specific. They also show high potency towards inhibition of hormone-regulating enzymes, e.g., aromatase, responsible for production of estrogen hormones, critically important in the causation of breast cancer. Third, preliminary studies suggest that methylation of the flavones results in more soluble derivatives, of great importance for pharmaceutical preparations. Importantly, although the data are limited, they also suggest that methylation of flavones results in derivatives with much diminished ability to produce unwanted side-effects. In conclusion, it appears that methylation of dietary flavones as well as other food products may produce derivatives with much improved health effects.

Regular Papers

Type of Paper: Article
Title: Diurnal Variation in the Phenolic Content of Lettuce in Response to UV Irradiation
Authors: Athanasios Koukounaras ¹, Anastasios S. Siomos ¹, Dimitrios Gerasopoulos ² and Katerina Karamanoli ³
Affiliations: ¹ Department of Horticulture, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece; E-Mail: siomos@agro.auth.gr (A.S.S.)
² Department of Food Science and Technology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
³ Department of Field Crops and Ecology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
Abstract: Fresh-cut lettuce has become popular. However, the browning of the cut surface is a major problem. Phenolic compounds could increase the browning susceptibility because they are natural substrates of oxidative enzymes such as polyphenol oxidase and peroxidase. The accumulation of phenolic compounds in lettuce is affected by a range of pre- and post-harvest factors. It has been reported that UV radiation induces phenolics in plant tissues. A further potentially important factor is the time of day that the lettuce is harvested, since leaf functional attributes are known to alter diurnally, but this subject is still unresolved. Several postharvest treatments (physical or chemical) are used in the control of browning. The objective of this study was to investigate whether a reduction of phenolics in harvested lettuce could be achieved by cultivation under UV block plastic film in combination by harvesting at different times during the course of the day in order to control browning of fresh-cut product. Red (Lollo Rosso) and green leaf (Paris Island) lettuce grown under one common and two types of plastic films that varied in transparency to UV radiation (designated as UV block and UV open) were harvest during two successive days at 06:30 (beginning of day), 13:30 (mid of day) and 20:30 (end of day). At harvest, total phenolics were determined by the Folin-Ciocalteu assay. After harvest, the leaves were cut at 2 cm segments stored for up to 6 days at 4 °C in plastic boxes covered with semipermeable film. The browning of the cut edges of the lettuce segments was evaluated visually every day.

Type of Paper: Article
Title: Influence of Different Ways of Cooking on the Total and Individual Antioxidant Content of Eight Vegetables
Authors: J. Pincemail, J. Dommes, J. O. Defraigne and C. Kevers
Affiliations: University of Liège - CHU, Dept of Cardiovascular Surgery - CREDEC B35 Sart Tilman 4000 Liège, Belgium; E-mail: J.Pincemail@chu.ulg.ac.be (J.P.)
Abstract: The public recommendation is to consume at least five or more servings (400 g) of fruits and vegetables daily in order to maximize prevention against cancer, cardiovascular diseases and diabetes. Such an effect of plant foods seems to be attributed to their high content in antioxidants able to decrease oxidative damages to key structures of the body including lipids, DNA and proteins. However, recent antioxidant databases have been elaborated on the basis of analytical data from raw plant material and do not, therefore, take in account the effect domestics of cooking on antioxidants. In the present study, 8 vegetables (broccoli, cabbage, potato, carrot, bean, Brussels sprout, tomato and leek) and 1 fruit (apple) were analyzed for the evolution of their total antioxidant capacity (ORAC) and their content of polyphenols (PPs) and ascorbic acid (AA) according to three way of cooking (water, steam, microwave). When compared to the dry weight, microwave produced an overall increase in polyphenols and ascorbic acid except for leek. ORAC values were either increased or remained unchanged. Water cooking was associated with negative effects on ORAC values except for potato, carrot and tomato. However, this was not systematically correlated with the evolution of PPs and AA. Steam cooking seems to well preserve the antioxidant content with respect of the three investigated parameters (except for AA in leek and Brussel sprouts). Our findings suggested that there was not an ideal way of cooking to preserve antioxidant qualities of all vegetables. Moreover, interpretation of data could be totally opposite according to the investigated parameters since no global correlation was found between ORAC, PPs and AA evolution after cooking.

Type of Paper: Article
Title: Phenols in Leaves and Bark of Fagus sylvatica as Determinants of Insect Occurrences
Authors: Panos V. Petrakis ¹, Kostas Spanos ² and Alan Feest ³
Affiliations: ¹ N. AG.RE.F., Institute for Mediterranean Forest Ecosystem Research, Laboratory of Entomology, Terma Alkmanos, 11528 Athens, Greece; E-Mail: pvpetrakis@fria.gr
² N.AG.RE.F., Forest Research Institute, 57006, Vassilika, Thessaloniki, Greece
³ Water and Management Research Centre, Faculty of Engineering, Univ. of Bristol, Bristol BS8 1TR, U.K. and ecosulis ltd, The Rickyard, Newton St. Loe, Bath, BA2 9BT, UK
Abstract: 1. Beech forests play an important role in all temperate and north Mediterranean ecosystems in Greece since they occupy extreme infertile montane soils. Until the last glacial maximum, Fagus sylvatica was confined to Southern Europe where it dominated and within the last thousand years dominated central Europe. Therefore it is suspected that beech decline is accompanied by a decline in the insect richness of beech forests.
2. We sampled four different beech forest types and we excluded coppice forests because they contained a lot of tourist insects from other deciduous trees (mainly Quercus, Ostrya, and Betulus). There were found 298 insect species in beech forests associated with the beech tree and its dead wood. Only a few were phytophagous whilst the majority included ground predators, detritivorous, and scavengers.
3. Whilst Fagus sylvatica belongs to the same family with Quercus and both genera include climax species, it exhibits great differences in terms of richness of the harbored entomofauna. Insect species that inhabit beech forests are almost one fifth of those species living in oak dominated forests besides the fact that beech is the most abundant central and north European tree.
4. There is an impressive paucity of monophagous species on beech trees and insect species are shared between co-occurring deciduous tree species and beech. For this lack the vegetation history and secondary plant chemistry have been implicated.
5. Bark biophenols from beech indicate that differences in plant secondary metabolites may be responsible for the differences in the richness of entomofauna among communities dominated by beech and other deciduous trees. Secondary plant chemistry and histochemistry may also be responsible for the mixing of beech with conifers or deciduous species.

Type of Paper: Review
Title: Flavonoids and Cardiovascular Health: A Review of Current Evidence
Authors: Sonia de Pascual-Teresa ¹, Diego A. Moreno ^2,* and Cristina García-Viguera ²
Affiliations: ¹ Departamento de Metabolismo y Nutrición, Instituto del Frío (IF), CSIC. Madrid, Spain
² Departamento de Ciencia y Tecnología de los Alimentos, Centro de Edafología y Biología Aplicada del Segura (CEBAS), CSIC, Murcia, Spain; E-Mail: dmoreno@cebas.csic.es (D.A.M.)
Abstract: Nowadays it is accepted that flavonoids present in foods and beverages, besides their technological relevance and organoleptic properties, may have potential health-promoting effects on consumers, as can be outlined from many epidemiological and experimental evidences. The beneficial biological effect of these food bioactives may be guided by two of their characteristic properties: their affinity for proteins and their antioxidant activity. Over the last 15 years, numerous publications have demonstrated that besides the demonstrated in vitro antioxidant capacity, certain phenolic compounds, such as anthocyanins, catechins, proanthocyanidins, and other non coloured flavonoids may regulate different signalling pathways involved in cell survival, growth and differentiation. In this review we will update the knowledge on the cardiovascular effects of anthocyanins, catechins, proanthocyanidins, and other non-coloured flavonoids as implied by the in vitro and clinical studies on these compounds. Nonetheless, we will also review the information on structure, distribution and bioavailability of these compounds being all necessary factors involved in the real importance of flavonoids in the human diet and the potenctial beneficial effect on cardiovascular disseases of these phytochemicals.

Type of Paper: Review
Title: Impact of Polyphenols on Glucose Metabolism
Authors: Kati Hanhineva, Riitta Törrönen, Isabel Bondia-Pons, Marjukka Kolehmainen, Hannu Mykkänen and Kaisa Poutanen
Affiliations: Food and Health Research Centre, Department of Clinical Nutrition, University of Kuopio, Finland; E-mail: Kati.Hanhineva@uku.fi (K.H.)
Abstract: Growing evidence indicates that various dietary polyphenols may influence glucose metabolism at many levels. In animal and human studies, polyphenols and foods or beverages rich in polyphenols have attenuated postprandial glycemic responses and fasting hyperglycemia, and improved acute insulin secretion, insulin sensitivity and glucose tolerance. The possible mechanisms include inhibition of carbohydrate digestion and glucose absorption in the intestine, stimulation of insulin secretion from the pancreatic b-cells, activation of insulin receptors and glucose uptake in the insulin-sensitive tissues, and modulation of intracellular signalling pathways and gene expression. Polyphenols may, therefore, have implications for prevention of insulin resistance, metabolic syndrome, and eventually type 2 diabetes.

Type of Paper: Review
Title: Polyphenols from Cacao and Vascular Health - A Critical Review
Authors: G. Rimbach, M. Melchin, J. Moehring and A. Wagner
Affiliations: Institute of Human Nutrition and Food Science, Christian Albrechts University Kiel, Germany; E-mail: rimbach@foodsci.uni-kiel.de (G.R.)
Abstract: Cacao is a rich source of dietary polyphenols. In vitro as well as cell culture data indicate that cacao may exhibit antioxidant, anti-inflammatory as well as antiatherogenic activity. Several molecular targets (e.g., NFkB, eNOS, ACE) have been recently identified which may partly explain potential beneficial cardiovascular effects of cacao polyphenols. However cacao polyphenol concentrations, as used in many cell culture studies, are not physiologically achievable. Furthermore, bioavailability studies indicate that plasma concentrations of cacao polyphenols following dietary intake are very low and in the nanomolar range. Human studies regarding the effect of cacao polyphenols on vascular health are often underpowered and lack a rigorous study design. If dietary cacao polyphenol intake is due to chocolate its high energy content needs to be taken into account. In order to determine potential health benefits of cacao polyphenols large scale, randomized, placebo controlled studies (ideally with a cross-over design) are warranted.