Phenolic acids can be classified as free, soluble and insoluble
bound phenolic acids (Renger and Steinhart, 2000). The free forms
of phenolic compounds are very rarely present in plants. Majority
of phenolic acids exists in the form of ester, acetal, or ethers and
some of the phenolic acids are linked either to structural compounds
of plants such as protein, dietary fiber or to longer or smaller
organic molecules such as glucose, maleic acid or to other
natural products (Robbins, 2003; Nardini et al., 2004). Acid hydrolysis
and saponification are the commonly used methods for
releasing bound phenolics by different workers. Esterases are also
used to cleave the ester bond, but not as popular as the other two
methods (Robbins, 2003).