The term “phenolic acids” generally describes the phenolic compounds having one carboxylic acid group. Phenolic acids or phenolcarboxylic acids are a subclass of a larger category of metabolites commonly referred to as “phenolics”, possess phenol moiety and resonance stabilized structure which causes the H-atom donation results in antioxidant property through radical scavenging mechanism.
Phenolic acid are found in the variety of plant-based foods viz. seeds, skins of fruits and leaves of vegetables contain them in highest concentrations.
Phenolic acids are mainly divided in to two sub-groups: hydroxybenzoic and hydroxycinnamic acid. Chemically, these compounds have at least one aromatic ring in which at least one hydrogen is substituted by a hydroxyl group.
If the carboxylic acid functional group is directly bonded to the phenol ring, the phenolic compound is termed as hydroxybenzoic acid. In this group the ones that stand out are protocatechuic acids, vanillic acids, syringic acid, gentisic acid, salicylic acid, p-hydroxybenzoic acid and gallic acid
When carboxylic acid functional group and the phenol ring are separated by two doubly bonded carbons (a C=C bond), phenolic compounds are termed as hydroxycinnamic acids. Among the cinnamic acids, p-coumaric, ferulic, caffeic and sinapic acids are the most common in nature.
Hydroxycinnamic acids, derived from cinnamic acid, present in foods often as simple esters with quinic acid or glucose. The most abundant soluble bound hydroxycinnamic acid present is chlorogenic acid (a combined from form of caffeic and quinic acids).
Phenolic acids are synthesized from the shikimate pathway from L-phenylalanine or Ltyrosine. Phenylalanine and tyrosine are very important amino acids in this pathway since these amino acids are the common precursors of the majority of the natural phenolic products.
Phenolic acid
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Common structures of hydroxyl-substituted cinnamic acid |
