The formation of FA in plants occurs through the metabolic route of shikimate pathway starting with aromatic amino acids, l-phenylalanine and l-tyrosine as key entities. Initially, phenylalanine and tyrosine are converted into cinnamic and p-coumaric acid with
the help of phenylalanine ammonia lyase and tyrosine ammonia lyase, respectively [17]. The p-coumaric acid gets converted into FA by hydroxylation and methylation reaction [16]. Oxidation and methylation of FA and other aromatic compounds give di- and tri-hydroxy derivatives of cinnamic acid, which takes part in the lignin formation together with check details FA. The conversion reactions occur during the formation of FA and other aromatic compounds, which are schematically represented in Fig. 2. In vivo studies on FA metabolism suggests that it gets converted into a variety of metabolites such as ferulic acid-sulfate, ferulic acid-glucuronide, ferulic acid-sulfoglucuronide (major metabolites in the plasma and urine of rats), ferulic acid-diglucuronide, feruloylglycine, this website m-hydroxyphenylpropionic acid, dihydroferulic acid, vanillic acid and vanilloylglycine [90] and [91]. The data obtained from these outcomes recommends that the major pathway of FA metabolism is the conjugation reaction with glucuronic acid and/or sulfate. The conjugation of FA takes place mainly in the liver through the activities of
sulfotransferases and uridine diphosphate (UDP) glucuronosyl transferases, while small amount of conjugation reaction also takes place in the intestinal mucosa and kidney [10],
[32] and [90]. A small portion of free FA possibly metabolized through β-oxidation in the liver [11]. A study was carried out by Overhage et al. with the help of Pseudomonas sp. strain HR199 at the end of twentieth century which revealed that the genes involved in the catabolic mechanism of FA were present on a DNA region, which was covered by two EcoRI fragments, E230 and E94, respectively. These genes were fcs, ech, and aat encoding for feruloyl coenzyme A synthetase, enoyl-CoA hydratase/aldolase, and β-ketothiolase, respectively [63]. Report on the degradation of FA into vanillin and other useful organic compounds through protocatechuate 4,5-cleavage (PCA) Fossariinae pathway in Sphingomonas paucimobilis SYK-6 confirmed that FA got converted into feruloyl-CoA by feruloyl-CoA synthetase (FerA), and further into HMPMP-CoA (4-hydroxy-3-methoxyphenyl-β-hydroxypropionyl-coenzyme A) with the help of feruloyl-CoA hydratases/lyases (FerB and FerB2). It subsequently resulted into vanillin with the removal of CH3COSCoA (acetyl coenzyme A), and finally vanillin transformed into pyruvate and oxaloacetate through the PCA pathway [43]. The end products of FA catabolism enter into the TCA (tricarboxylic acid cycle), and produce energy in the biological system as shown in Fig. 3.