Plant polyphenols, health benefits

EPIDEMIOLOGIC EVIDENCE OF PLANT POLYPHENOL HEALTH BENEFITS... 

Plant polyphenols have been of interest for long time owing to their role in plant pigmentation, reproduction and protection against predators and pathogens. Recently, interest in the biological effects of plant polyphenols (particularly flavonoids) has increased, because of the the potential health benefits associated with some dietary polyphenols. This... 

In association with well-known health benefits related to the consumption of fruit- and vegetable-rich diets, research on the protective effects of plant-derived phenolic compounds (polyphenols) has developed notably in recent years. In particular, their antioxidant properties have been the objective of extensive research. However these phenolics are the target of an array of chemical reactions that, if confirmed to occur in vivo, would contribute to their health promoting effects. It is now emerging that both parent compounds and their metabolites produced after ingestion can regulate cell and tissue functions by both antioxidant and nonantioxidant mechanisms. This volume provides the latest evidence supporting these concepts. 

Ellagitannins are among the most diverse and structurally complex class of polyphenolics in plants. They are important contributors to color, flavor and stability in fruits as well as oaked wine and distilled spirits. Recently, consumption of ellagitannins has also been linked to potential health benefits. The extraction, isolation, and identification... 

We must be cautious about what conclusions we draw from new research on polyphenols in relation to superfruits. The polyphenol class as a whole is a highly productive research topic in food and medical science. While scientists are continually adding to what we know about the possible impact of these plant compounds on human health, we need to be wary about the use of unconfirmed results for marketing by manufacturers eager to have a competitive edge in selling superfruit products. This practice unfortunately leads to false claims of effectiveness and to their acceptance by consumers as fact when actually the research is too premature to warrant conclusions about health benefits. 

Second, plant compounds called phytochemicals are nonnutrient components of plant foods that may impart health benefits, similar to the pigment antioxidant polyphenols, on the basis of which nearly all superfruit juices are promoted with eye-catching advertisements. Because these phytochemicals await final scientific proof of what they really do in the human body, they are regarded neither as nutrients nor as essential to health. 

Resveratrol (82) is a polyphenolic antioxidant found in many plants, including grapes, nuts, and berries. First isolated in 1940 from the roots of white hellebore Veratrum grandiflorum), it has gained prominence through its association with the highly publicized French Paradox linked to the drinking of red wine. There is an extensive literature on the multiple health benefits attributed to resveratrol and interested readers are referred to several recent reviews that summarize the available data. ... 

Polyphenols are the most important phytochemicals found in a variety of fruits, vegetables, and plant-based foods. Currently there is an increasing interest for the separation, characterization, and valorification of these compounds due to their bioactive properties, health benefits, and potential use as natural antioxidants in foods, pharmaceuticals, and cosmetics. 

Details about structure, biosynthesis, and classification of phenolics are described in the other chapters in this handbook. Plant phenolics have a distinctive ability to form non-covalent, intermolecular complexes with each other and with both large and small molecules. Recognition of the antioxidant activities of many polyphenols has established correlation with the health benefits by such compounds [34]. This leads to the development of commercial products containing free-radical-scavenging phytochemical mixtures, for example, Pycnogenol (procyanidin extracted from Pinus maritima). Table 82.2 represents a list of polyphenolic compounds used in nutraceuticals and their biologic effects on human health. 

The potential health benefits of plant polyphenols, such as the flavonoids, have been addressed over the years in the framework of the oxidative stress concept. Oxidative stress, as initially formulated by Sies (1985), refers to an imbalance in the dynamic equilibrium between oxidants and antioxidants that favors the formers, potentially leading to damage. As several diseases are supposed to mechanistically involve oxidative stress, such as atherosclerosis, ischemia-reperfusion injury, cancer, and neurodegenerative disorders (Halliwell Gutteridge, 1999), an impressive number of studies on the in vitro antioxidant activity of polyphenols have spotted these compounds as putatively useful to counteract the deleterious oxidant imbalance associated with disease. However, as will be discussed later, because of limited bioavailability and recent updated concept of oxidative stress, the putative activity of polyphenols as global antioxidants is a limited and simplistic view of polyphenol activity in vivo that can be scarcely supported by experimental data. 

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