On the mechanism behind enhanced antibacterial activity of alkyl gallate esters against foodborne pathogens and its application in Chinese icefish preservation.

The objective of this study was to investigate antibacterial activities and action mode of alkyl gallates against three food-related bacteria. Results show that the length of the alkyl chain plays a critical role in eliciting their antibacterial activities and octyl gallate (GAC8) exhibited an outstanding bactericidal effect against these strains. A possible bactericidal mechanism of GAC8 against E. coli was fully elucidated by analyzing associated changes in cellular functions of E. coli, including assessments of membrane modification and intracellular oxidation state. Our data strongly suggested that GAC8 functions outside and inside the bacterial membrane and causes increased intracellular reactive oxygen species (hydroxyl radicals) and subsequent oxidative damage. We demonstrated that the hydroxyl radical formation induced by GAC8 is the end product of an oxidative damage cellular death pathway involving a transient depletion of NADH, the tricarboxylic acid cycle, intrinsic redox cycling activities, and stimulation of the Fenton reaction. Also, chitosan-based edible films containing GAC8 have unique superiorities for icefish preservation at 4 °C. This research highlights the effectiveness of GAC8 as an attractive antibacterial, which possesses both antioxidant and antibacterial activities and can be used as a multifunctional food additive combined with the benefit of active packaging for food preservations.

Antimicrobial mechanism of alkyl gallates against Escherichia coli and Staphylococcus aureus and its combined effect with electrospun nanofibers on Chinese Taihu icefish preservation.

The objective of this study was to investigate the antibacterial activity and potential mechanism of alkyl gallates against Escherichia coli and Staphylococcus aureus. Results show that the length of the alkyl chain plays a pivotal role in eliciting the activity and octyl gallate (OG) exerted excellent bactericidal activity through a multiple bactericidal mechanism. OG functions against both bacteria through damaging bacterial cell wall integrity, permeating into cells and then interacting with DNA, as well as disturbing the activity of the respiratory electron transport chain to induce a high-level toxic ROS (hydroxyl radicals) generation and up-regulation of the ROS genes. Also, electrospun nanofibers with OG have unique superiorities for maintaining the freshness of the icefish (4 °C). This research not only provides a more in-depth understanding of the interaction between OG and microorganisms but also highlights the great promise of using OG as a safe multi-functionalized food additive for food preservations.

New Horizons in Microbiological Food Safety: Ultraefficient Photodynamic Inactivation Based on a Gallic Acid Derivative and UV-A Light and Its Application with Electrospun Cyclodextrin Nanofibers.

An excellent bactericidal effect of octyl gallate (OG)-mediated photodynamic inactivation (PDI) against foodborne pathogens (Escherichia coli and Staphylococcus aureus) was evaluated in relation to the mode of action. UV-A irradiation (wavelength, 365 nm; irradiance, 8.254 ± 0.18 mW/cm2) of the bacterial suspension containing 0.15 mM OG could lead to a >5-log reduction of viable cell counts within 30 min for E. coli and only 5 min for S. aureus. Reactive oxygen species (ROS) formation was considered the main reason for the bactericidal effect of OG + UV-A light treatment because toxic ROS induced by OG-mediated PDI could attack the cellular wall, proteins, and DNA of microbes. Moreover, the bactericidal effect, as well as the yields of ROS, depended on OG concentrations, irradiation time, and laser output power. Furthermore, we prepared an edible photodynamic antimicrobial membrane comprising electrospun cyclodextrin nanofibers (NFs) by embedding OG. The resultant OG/HPßCD NFs (273.6 µg/mL) under UV-A irradiation for 30 min (14.58 J/cm) could cause a great reduction (>5-log) of viable bacterial counts of E. coli. The in situ photodynamic antibacterial activity of OG/HPßCD NF-based packaging was evaluated during the Chinese giant salamander storage. Overall, this research highlights the dual functionalities (antibacterial and photodynamic properties) of OG as both an antibacterial agent and photosensitizer and the effectiveness of electrospun NFs containing OG as an active antibacterial packaging material for food preservation upon UV light illumination.

Lipophilic ferulic acid derivatives protect PC12 cells against oxidative damage via modulating ß-amyloid aggregation and activating Nrf2 enzymes.

Ferulic acid (FA) has been shown to have a neuroprotective effect on Alzheimer's disease induced by amyloid-beta (Aß) neurotoxicity. This work aims to ascertain the structure-activity relationship of FA and its alkyl esters (FAEs) for evaluating the antioxidant activities in PC12 cells and Aß1-42 aggregation inhibitory activities in vitro, as well as the signaling mechanisms against oxidative stress elicited by Aß1-42 in PC12 cells. Our data showed that alterations in the subcellular localization and cytotoxicity of FAEs caused by the lipophilicity of FA were crucial when evaluating their antioxidant capacities. Pre-treating cells with butyl ferulate (FAC4) significantly attenuated Aß1-42-evoked intracellular ROS formation. Besides, FAC4 exhibited the highest Aß1-42 aggregation inhibitory effectiveness. The molecular docking results showed that FAC4 binds to amide NH in Gln15 and Lys16 via a hydrogen bond. Notably, FAC4 could upregulate antioxidant defense systems by modulating the Keap1-Nrf2-ARE signaling pathway. Identification of the functions of FAEs could be useful in developing food supplements or drugs for treating AD.

Alkyl Ferulate Esters as Multifunctional Food Additives: Antibacterial Activity and Mode of Action against Escherichia coli in Vitro.

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 ß-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.

Lipase-catalyzed esterification of ferulic acid with lauryl alcohol in ionic liquids and antibacterial properties in vitro against three food-related bacteria.

Lauryl ferulate (LF) was synthesized through lipase-catalyzed esterification of ferulic acid (FA) with lauryl alcohol in a novel ionic liquid ([(EO)-3C-im][NTf2]), and its antibacterial activities was evaluated in vitro against three food-related bacteria. [(EO)-3C-im][NTf2] was first synthesized through incorporating alkyl ether moiety into the double imidazolium ring. [(EO)-3C-im][NTf2] containing hexane was found to be the most suitable for this reaction. The effects of various parameters were studied, and the maximum yield of LF (90.1%) was obtained in the optimum reaction conditions, in [(EO)-3C-im][NTf2]/hexane (VILs:Vhexane=1:1) system, 0.08mmol/mL of FA concentration, 50mg/mL Novozym 435, 60°C. LF exhibited a stronger antibacterial activity against Gram-negative (25 mm) than Gram-positive (21.5-23.2 mm) bacteria. The lowest MIC value was seen for E. coli (1.25mM), followed by L. Monocytogenes (2.5mM) and S.aureus (5mM). The MBCs for L. Monocytogenes, S.aureus and E. coli were 10, 20 and 5mM.