p-Coumaric acid was used as a substrate to study the enzyme activity of 4-hydroxyphenylacetate 3-hydroxylase (4HPA3H) found in E.coli which inturn was used in biosynthesis of caffeic acid . Phenylpropanoids (p-Coumaric acid) esterified with sucrose was essential for higher antimicrobial activity of vanicosides . The FSI (flavone synthase I) - expressing recombinant strain produced 50% more apigenin and six times less naringenin than the FSII (membrane-bound flavone synthase II) - expressing recombinant strain when p-coumaric acid was used as a precursor phenylpropanoid acid.