Effect of Pentyl Alcohol Isomerism on the Biocatalytic Synthesis, Process Efficiency, and Antioxidant Properties of Dihydrocaffeic Acid Esters

Alkyl-chain architecture may influence both the enzymatic synthesis and antioxidant performance of phenolic esters. This study examined the esterification of dihydrocaffeic acid with four isomeric C5 alcohols catalyzed by immobilized Candida antarctica lipase B (CALB). The isolated products were evaluated using process metrics, NMR, physicochemical predictions, density functional theory calculations, DPPH and ABTS assays, and pressure differential scanning calorimetry in flaxseed and grape seed oils. The isolated yields of n-pentyl, 2-methylbutyl, and 3-methylbutyl dihydrocaffeates were 61.25%, 49.87%, and 53.08%, respectively, whereas no measurable amount of the 2,2-dimethylpropyl ester was isolated under the applied conditions. The linear derivative showed the highest biocatalyst productivity and the most favorable reaction-stage material-efficiency indices. DPPH activity was similar across all isolated esters, whereas the 3-methylbutyl derivative showed the strongest ABTS activity. The lowest calculated O–H bond dissociation enthalpy was obtained for the 2-methylbutyl derivative. At 0.01%, all three esters provided greater oxidative protection than butylated hydroxytoluene under the applied PDSC conditions. Their effects were similar in flaxseed oil, whereas the n-pentyl derivative was clearly superior in grape seed oil. Under the applied reaction conditions, the linear and branched alcohols showed different synthesis outcomes, whereas antioxidant performance in oils was strongly matrix-dependent and not predicted by any single computational or solution-based descriptor.