Antioxidant properties and efficacies of synthesized alkyl caffeates, ferulates, and coumarates

Caffeic, ferulic, and coumaric acids were lipophilized with saturated fatty alcohols (C1-C20). The antioxidant properties of these hydroxycinnamic acids and their alkyl esters were evaluated in various assays. Furthermore, the antioxidant efficiency of the compounds was evaluated in a simple o/w microemulsion using the conjugated autoxidizable triene (CAT) assay. All evaluated phenolipids had radical scavenging, reducing power, and metal chelating properties. Only caffeic acid and caffeates were able to form a complex with iron via their catechol group in the phenolic ring. In the o/w emulsion, the medium chain phenolipids of the three homologues series were most efficient. The antioxidant properties and efficacies were dependent upon functional groups substituted to the ring structure and were in the following order: caffeic acid and caffeates > ferulic acid and ferulates > coumaric acid and coumarates. Moreover, the results demonstrated that the test system has an impact on the antioxidative properties measured.