Geometric isomers of ferulic acid and ethyl ferulate: Photo- and thermal-induced isomerization behavior, physicochemical properties, antioxidant capacity, and enzyme inhibitory activities.

Highly purified (>99%) cis isomers of ferulic acid (FA) and ethyl ferulate (EF) were prepared from the corresponding trans isomers by photoisomerization and chromatographic separation, and the trans and cis isomers were compared for isomer-dependent differences in isomerization behavior, physicochemical properties, antioxidant capacity, and enzyme inhibitory activities. Photoisomerization studies showed different visible-light responses for FA and EF. Isomerization markedly altered UV-Vis spectra, molar absorption coefficient, crystallinity, and melting behavior; notably, trans-EF was crystalline, whereas cis-EF was amorphous. Antioxidant profiling indicated that singlet oxygen quenching tended to favor the trans isomers, whereas free-radical scavenging tended to favor the cis isomers. Enzyme inhibitory activities were broadly comparable between isomers, although significant differences were observed for selected endpoints, including higher collagenase inhibition for the trans isomers and a tendency for higher renin inhibition for the cis isomers. These results provide an isomer-aware basis for the development of FA- and EF-related products.