Phenolic Phytochemical Ingredients And Benefits

Phenolic phytochemicals are secondary metabolites synthesized by plants to protect themselves against biological and environmental stresses such as pathogen attack or high energy radiation exposure (1,2). These compounds involved in the plant defense response are one of the most abundant classes of phytochemicals and are also invariably important components of our diets (3,4,5). Commonly consumed fruits such as apples, bananas, grapes, and several types of berries and their beverages are examples of plant foods as sufficiently rich sources of phenolic phytochemicals. Similar phytochemicals in our diet are also obtained from diverse commonly consumed vegetables such as tomato, cabbage, and onions to grains such as cereals and millets as well as legumes such as soybean, common beans, mung beans, fava beans, and peas, depending on the specific regions of the world (4,5,6). In addition many different types of herbs and spices containing phenolic phytochemicals are widely consumed through the diet. Therefore, there are many different types of phenolic phytochemicals from the diet that are mediators of different biological functions for health and wellbeing. The profile of phenolic phytochemicals is often a characteristic of that plant species and is a result of the evolutionary pressures experienced by that species (5,6,7). The most abundant phenolic compounds in fruits are flavonols and flavonoids. Flavonoids, isoflavonoids, phenolic acids, and tannins are important phenolic phytochemicals in many legumes (5,6,7). Biphenyls such as rosmarinic acid are common in many herbs (1).

Chemically phenolic phytochemicals refers to a wide range of chemical compounds containing at least one aromatic ring and a hydroxyl substituent. Metabolic processing in plants after their synthesis results in chemical variations in basic phenolic structure (8). More than 8000 different phenolic structures, categorized into 10 subclasses, have been identified and are a result of differences in substituent groups and linkages. Structurally different phenolic phytochemicals having distinct properties range from simple molecules (e.g., phenolic acids with a single ring structure) to biphenyls and flavanoids having two or three phenolic rings (9,10). Polyphenols that contain >10 phenolic groups are another abundant group of phenolic phytochemicals in fruits and vegetables. Proanthocyanidins, tannins, and their derivatives phlorotannins are often referred to as polyphenols (9,10).

Phenolic phytochemicals are synthesized in plants via a common biosynthetic pathway and derive precursors from the shikimate-phenylpropanoid and the acetate-malonate (polyketide) pathways (1,11). Cinnamic acid, coumaric acid, and caffeic acid, and their derivatives are widespread in fruits, vegetables, and herbs and are derived primarily from the shikimate/phenylpropanoid pathway (1). Oxidative modifications of side chains produce benzoic acid derivatives, which include protocatechuic acid and its positional isomer gentisic acid. Fruits and legumes are especially rich sources of another group of phenolic phytochemicals called flavonoids and iso-lavonoids, which constitute the most abundant group of phenolic phytochemicals derived from the phenylpropanoid-acetate-malonate pathway (2,11).

Flavonoids are subdivided into several families such as flavonols, flavones, flava-nols, isoflavones, and antocyanidins, which are formed as a result of hydroxylation, meth-ylation, isoprenylation, dimerization, and glycosylation of the substituents in the aromatic rings (2,11). Phenolic phytochemicals are often esterified with sugars and other chemicals such as quinic acid to increase their solubility and to prevent their enzymatic and chemical degradation. Esterification also helps to target the phenolics to specific parts of the plant (11). Phenolic phytochemicals esterified via their hydroxyl groups to sugars are called glycosides. The sugar most commonly involved in esterification is glucose. However, the glycosides of phenolics with galactose, sucrose, and rhamnose are also found in some plant species (11).

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  • cerdic
    What is the importance of phenols as phytochemicals?
    2 years ago

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