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This work aims to prepare ferulic acid alkyl esters (FAEs) through the lipase-catalyzed reaction between methyl ferulate and various fatty alcohols in deep eutectic solvents and ascertain their antibacterial activities and mechanisms. Screens of antibacterial effects of FAEs against Escherichia coli ATCC 25922 ( E. coli) and Listeria monocytogenes ATCC 19115 ( L. monocytogenes) revealed that hexyl ferulate (FAC6) exerted excellent bacteriostatic and bactericidal effects on E. coli and L. monocytogenes (minimum inhibitory concentration (MIC): 1.6 and 0.1 mM, minimum bactericidal concentration (MBC): 25.6 and 0.2 mM, respectively). The antibacterial mechanism of FAC6 against E. coli was systematically studied to facilitate its practical use as a food additive with multifunctionalities. The growth and time-kill curves implied the partial cell lysis and inhibition of the growth of E. coli caused by FAC6. The result related to propidium iodide uptake and cell constituents' leakage (K + , proteins, nucleotides, and β-galactosidase) implied that bacterial cytomembranes were substantially compromised by FAC6. Variations on morphology and cardiolipin microdomains and membrane hyperpolarization of cells visually verified that FAC6 induced cell elongation and destructed the cell membrane with cell wall perforation. SDS-PAGE analysis and alterations of fluorescence spectra of bacterial membrane proteins manifested that FAC6 caused significant changes in constitutions and conformation of membrane proteins. Furthermore, it also could bind to minor grooves of E. coli DNA to form complexes. Meanwhile, FAC6 exhibited antibiofilm formation activity. These findings indicated that that FAC6 has promising potential to be developed as a multifunctional food additive.

The absolute configurations of 2-oxygenated phenylethanoid glycosides were conveniently determined by (1)H NMR spectroscopy. A comparison of the chemical shift differences (Δδ) of the diastereotopic methylene protons (H-1) demonstrate that a large chemical shift difference corresponds to an R configuration and a small chemical shift difference indicates S for the 2-alkoxy form. However, the situation is contrary to that of the 2-hydroxy form. Furthermore, the mechanism underlying this result is discussed based on the visualized conformations of such compounds.