DIETARY POLYPHENOLS: AN OVERVIEWHTML Full Text
DIETARY POLYPHENOLS: AN OVERVIEW
A. P. Attanayake
Department of Biochemistry, Faculty of Medicine, University of Ruhuna, Galle, Sri Lanka.
ABSTRACT: Dietary polyphenols, mainly phenolic acids and flavonoids, are the primary sources of antioxidants that can be generally recommended for human consumption. Polyphenols are derived from plant-based food, including fruits, vegetables, spices, herbs, etc. In the present era, there has been a great interest in the health benefits of dietary polyphenols against oxidative stress-related diseases such as diabetes mellitus, cancer, chronic kidney disease, etc. Here, the content presents an overview of dietary polyphenols in the context of relevance to human health.
Keywords: Antioxidant activity, Chronic diseases, Polyphenols
INTRODUCTION: Polyphenols are the largest group of phytonutrients that exert different biological activities that are beneficial to human health. Fruits, vegetables, cereals, and plant-derived beverages such as fruit juices, tea, coffee, and red wine are the main dietary sources of polyphenols. It is found that human consumption of polyphenols is, generally higher than any other phytonutrient or dietary antioxidant 1, 2, 3. The scientific and research interest in biological activities of polyphenols for maintaining human health approximately started in the late 1980s and tremendous progress has been made to date 4, 5. Polyphenols are widely distributed in the plant kingdom. More than 8,000 distinct polyphenol structures are reported and identified from different plants 6.
Polyphenols are the products of secondary metabolism and can vary from simple phenolic acids to highly polymerized molecules such as tannins. Polyphenols exist primarily in conjugated forms with one or more sugar residues, via glycosides, linked to one or more of the many hydroxyl groups 4, 7. Polyphenols can be classified according to their source of origins such as tea polyphenols, grape polyphenols, and apple polyphenols, or their chemical structures. When the basic chemical structure is of concern, polyphenols can be divided into basic groups as lignans, phenolic acids, flavonoids, stilbenes 8.
The most common and important low molecular weight phenolic compounds are simple phenolic derivatives and flavonoids 9. Phenolic acids are simple molecules such as caffeic acid, vanillin, and coumaric acid that account for approximately one-third of the total dietary intake of polyphenols. Many flavonoids present in plants as aglycones although they are most commonly found as glycoside derivatives. Flavonoids account for the remaining two-thirds. Flavonoids can be further subdivided into classes including flavonols, flavanones, flavanols, flavones, anthocyanins, isoflavones with more than 4,000 described compounds 10, 11, 12.
Occurrence: Polyphenol compounds are distributed in plants at the tissue, cellular, and subcellular levels. However, the distribution of polyphenols is not uniform. Insoluble polyphenols are mainly found in cell walls; however, soluble polyphenols are present within the plant cell vacuoles 13. Numerous factors affect the polyphenol content of plants, such as climatic and environmental factors, processing, storage, degree of ripeness at the time of harvest, etc. The outer layers of plants contain higher levels of polyphenols than those located in the inner parts 10.
In most cases, food contains complex mixtures of polyphenols 14. Flavonoids are mostly found in all plant-based food; fruits, vegetables, cereals, fruit juices, tea, wine, infusions, etc., whereas flavanones and isoflavones are specific to particular foods 15. The degree of ripeness considerably affects the concentrations and proportions of various polyphenols 16, 17. The easy oxidation of the polyphenols may lead to change in the content of polyphenols in plants 16. Different types of cooking methods also affect the polyphenol content of foods since polyphenols are present in plant vacuoles and in cellular structures that require softening during the cooking process to maximize polyphenol release. However, most of the vegetables can lose 75% to 100% of their initial polyphenol content during boiling, whereas steaming and frying losses are considerably lower than fresh vegetables 18.
Bioavailability: Dietary intake of plant polyphenols can vary considerably and be quite high. However, ultimately, the nutritional impact and subsequent systemic effects depend on the fate of polyphenols in the human digestive tract 19, 20. Physicochemical characteristics of polyphenols appear to dictate absorption and metabolism and are determined primarily by the chemical structures 6, 7. Relatively small molecular weight phenolic acids, i.e., gallic acid and isoflavones are easily absorbed through the gut followed by catechins, flavanones, and quercetin glucosides. Larger polyphenols such as proanthocyanidins are very poorly absorbed. The main difficulty with incorporating polyphenols into existing products is to present them in a form that is bioavailable 21. Accordingly, the total polyphenol metabolite content in plasma or urine after intake of dietary polyphenols is generally low 2, 22. It was further noted that bioavailability differs greatly from one polyphenol to another and the most abundant dietary polyphenol was not necessarily the one leading to the highest levels of active metabolites in plasma. The maximum plasma concentrations of polyphenol metabolite content are less than 10 μmol/L 23. The physicochemical characteristics of polyphenols likely contribute to the disparity in results between the epidemiological studies and in-vitro data, which may reflect, in part, relatively poor bioavailability, rapid metabolism, and excretion of polyphenols 24.
Scientists are taking efforts to increase the bioavailability of polyphenols, but several considerations and potential impediments exist, including solubility, permeability, metabolism, excretion, target tissue uptake using nanoparticle-based approaches and disposition 21. Initial strategies for improving the bioavailability of dietary polyphenol supplements include changes to polyphenol structure, which may affect the solubility and dissolution, and the use of pharmaceutical recipients 21. An additional consideration is that degradation and absorption of polyphenols within the gastrointestinal tract depend on the intestinal microflora and gut enzymes, which may significantly change bioavailability 25.
Metabolism of Polyphenols: Dietary polyphenols are initially metabolized, within the gastrointestinal tract. Glycosides are hydrolyzed to their corresponding aglycones before the absorption, aglycones, and low molecular weight polyphenols are absorbed directly 2. Polyphenols that are not absorbed are transported to the colon where they can be readily hydrolyzed by colonic microflora to simpler chemical compounds and eliminated in the feces or further modified. Bacterial fermentation of the glycones effectively releases the polyphenol from fiber permitting subsequent metabolism similar to other aglycones 26.
Polyphenols and Human Diseases: Correlations between the intake of polyphenols and reduced incidence of chronic diseases have been firmly established using different in-vivo models in the past decades. The in cooperation of polyphenols in the prevention and management of inflammation and oxidative stress related pathologies is emerging 4. Epidemiological studies have repeatedly shown an inverse association between the occurrence of chronic diseases and the consumption of polyphenolic-rich diet 27, 28. It is well established that polyphenol-rich foods and beverages may increase plasma antioxidant capacity 2. This increase in the antioxidative capacity of plasma following the consumption of polyphenol-rich food may be explained either by the presence of reducing polyphenols and their metabolites in plasma, by their effects upon concentrations of other reducing agents via sparing effects of polyphenols on other endogenous antioxidants, or by their effect on the absorption of pro-oxidative food components, such as iron 29. Consumption of antioxidants has been associated with reduced levels of oxidative damage to lymphocytic DNA 30. There are increasing evidence that as antioxidants, polyphenols may protect cell constituents against oxidative damage and therefore, limit the risk of various degenerative diseases associated with oxidative stress 31, 32.
CONCLUSION: The content outlined in this review provides a general overview of dietary polyphenols, occurrence and content, bioavailability, metabolism, and their relevance to human health. Dietary polyphenols are beneficial against the development and progression of much chronic oxidative stress-related pathological conditions. The role of polyphenols in human health and disease is still an interesting area of research and warranted further scientific studies.
CONFLICT OF INTEREST: Nil
- Scalbert AG and Williamson: Dietary intake and bioavailability of polyphenols. Journal of Nutrition 2000; 130: 2073S-20785S.
- Scalbert A, Johnson IT and Saltmarsh M: Polyphenols: antioxidants and beyond. American Journal of Clinical Nutrition 2005; 81: 215S-217S.
- Williamson G: The role of polyphenols in modern nutrition. Nutrition Bulletin 2017; 42(3): 226-235.
- Shen T, Han X, Wang X, Fan P, Ren D and Lou H: Protective effects of dietary polyphenols in human diseases and mechanisms of action. In Nutritional antioxidant therapies: Treatments and Perspectives. Springer International Publishing AG. Switzerland 2007; 307-346.
- Adebooye OC, Alashi AM and Aluko RE: A brief review on emerging trends in global polyphenol research. Journal of Food Biochemistry 2018; e12519.
- Rio DD, Rodriguez-Mateos A, Spencer JPE, Borges T and Crozier A: Dietary polyphenolics in human health: Structures, bioavailability and evidence of protective effects against chronic diseases. Antioxidants and Redox Signaling 2013; 18(14): 1818-1892.
- Martin KR and Appel CL: Polyphenols as dietary supplements: A double-edged sword. Nutrition and Dietary Supplements 2010; 2: 1-12.
- Crozier A, Jaganath IB and Clifford MN: Dietary phenolics: Chemistry, new magic bullet? Proceedings of the Nutrition Society 2003; 62: 599-603.
- Alkhatib A, Tsang C, Tiss A, Bahorun T, Arefanian H, Barake R, Khadir A and Tuomilehto J: Functional foods and lifestyle approaches for diabetes prevention and management. Nutrients 2017; 9: 1310.
- Pandey KB and Rizvi SI: Plant polyphenols as dietary antioxidants in human health and disease. Oxidative Medicine and Cell Longevity 2009; 2(5): 270-278.
- Kumar S and Pandey AK: Chemistry and biological activities of flavonoids: An overview. Scientific World Journal 2013; e162750.
- Carmona-Hernandez JC, Ceballos-López LM and González-Correa CH: Polyphenols and flavonoids in Colombian fruit and vegetables - applications and benefits: A review. Journal of Food Nutrition Research 2018; 6 (3): 76-181.
- Wink M: Compartmentation of secondary metabolites and xenobiotics in plant vacuoles. Advances in Botanical Research 1997; 25: 141-169.
- Alkhalidy HY and Liu WD: Dietary flavonoids in the prevention of T2D: An overview. Nutrients 2018: 10: 438.
- Gharras HEI: Polyphenols: food sources, properties and applications - A review. International Journal of Food Science and Technology 2009; 44: 251-2518.
- Manach C, Scalbert A, Morand C, Rémésy C and Jimenez L: Polyphenols: food sources and bioavailability. American Journal of Clinical Nutrition 2004; 79: 727-747.
- Simon BF, Perez-Ilzarbe J, Hernandez T, Gomez-Cordoves C and Estrella I: Importance of phenolic compounds for the characterization of fruit juices. Journal of Agricultural and Food Chemistry 1992; 40: 1531-1535.
- Miglio C, Chiavaro E, Visconti A, Fogliano V and Pellegrini N: Effects of different cooking methods on nutritional and physicochemical characteristics of selected vegetables. Journal of Agricultural and Food Chemistry 2008; 56: 139-147.
- Ovaskainen M, Torronen R, Koponen JM, Sinkko H, Hellstrom J, Reinivuo H and Mattila P: Dietary intake and major food sources of polyphenols in Finnish adults. Journal of Nutrition 2008; 138: (3): 562-566.
- Santhakumara AB, Battinob M and Alvarez-Suarezc MJM: Dietary polyphenols: Structures, bioavailability and protective effects against atherosclerosis. Food and Chemical Toxicology 2018; 113: 49-65.
- Hu M: Commentary: Bioavailability of flavonoids and polyphenols: Call to arms Molecular Pharmaceutics 2007; 4: 803-806.
- Jew S, Suhad S, Mweis A and Jones PJH: Evolution of the human diet: Linking our ancestral diet to modern functional foods as a means of chronic disease prevention. Journal of Medicinal Food 2009; 12 (5): 925-934.
- Kroon PA, Clifford MN, Crozier A, Day AJ, Donovan JL, Manach C and Williamson G: How should we assess the effects of exposure to dietary polyphenols in-vitro? American Journal of Clinical Nutrition 2004; 80(1): 15-21.
- Duthie GG, Gardner PT and Kyle JAM: Plant poly-phenols: are they the new magic bullet? Proc Nutr Soc 2003; 62(3): 599-603.
- Marín L, Miguélez EM, Villar CJ and Lombó F: Bioavailability of dietary polyphenols and gut microbiota metabolism: Antimicrobial properties. Biomed Research International 2015; 905215.
- Bravo L: Polyphenols: Chemistry, dietary sources, metabolism, and nutritional significance. Nutrition Reviews 1998; 56: 317-333.
- Arts ICW and Hollman PC: Polyphenols and disease risk in epidemiologic studies. American Journal of Clinical Nutrition 2005; 81: 317-325.
- Clifford MN: Chlorogenic acids and other cinnamates. Nature, occurrence, dietary burden, absorption and metabolism. Journal of Science of Food and Agriculture 2000; 80: 1033-1043.
- Meydani M and Hasan ST: Dietary polyphenols and obesity. Nutrients 2010; 2: 737-751.
- Vauzour D, Rodriguez-Mateos A, Corona G, Oruna-Concha MJ and Spencer JPE: Polyphenols and human health: prevention of disease and mechanisms of action. Nutrients 2010; 2: 1106-1131.
- Shay J, Elbaz HA, Lee I, Zielske SP, Malek MH and Hüttemann M: Molecular mechanisms and therapeutic effects of (−)-Epicatechin and other polyphenols in cancer, inflammation, diabetes, and neurodegeneration. Oxidative Medicine and Cell Longevity 2015; 1-13.
- Hussain T, Tan B, Yin Y, Blachier F, Tossou MCB and Rahu. N: Oxidative stress and inflammation: what polyphenols can do for us? Oxidative Medicine and Cellular Longevity 2016; e7432797.
How to cite this article:
Attanayake AP: Dietary polyphenols: An overview. Int J Life Sci & Rev 2018; 4(11): 176-79. doi: 10.13040/IJPSR.0975-8232.IJLSR.4(11).176-79.
All © 2015 are reserved by International Journal of Life Sciences and Review. This Journal licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
A. P. Attanayake
Department of Biochemistry, Faculty of Medicine, University of Ruhuna, Galle, Sri Lanka.
10 September 2018
24 September 2018
22 October 2018
01 November 2018