Antifungal effects of thymol and salicylic acid on cell membrane and mitochondria of Rhizopus stolonifer and their application in postharvest preservation of tomatoes.

Synergistic inhibition effect of citral and eugenol against Aspergillus niger and their application in bread preservation.

Structured abstracts Background Pollution of foodborne microbial biofilms is a serious problem in the food industry. Microorganisms in the biofilms become insensitive to environmental stresses and increase tolerance to antimicrobial agents, therefore, making them extremely hard to be inactivated by conventional methods. Ultrasound-involved emerging strategies offer options for effectively controlling the biofilms formed on either food contact surfaces or real foods. Scope and approach This review emphasizes the significances of either ultrasonication alone or combined with other strategies for controlling foodborne microbial biofilms. Key findings and conclusions Ultrasound as an emerging technology would effectively destroy biofilm structure and partially inactivate microorganisms in the biofilms; however, stimulated the growth of microbes may happen after treatment of low-frequency and low-intensity ultrasound. Combined ultrasound (especially low-frequency and high-intensity ultrasound) and chemical disinfectants shows a synergistic effect with a relatively high proportion of inactivated microbes in the biofilms compared with that adopted one strategy alone. Ozone and electrolyzed water are also developed for inactivating microbes and removing the biofilms after combining with the ultrasound. Combined treatment of ultrasonication and chelating agents or enzymes is proved to effectively remove the biofilms instead of achieving a strong bactericidal effect. Mechanical oscillation, localized high temperature and pressure, as well as free radicals generated by cavitation during the ultrasonication can partially destroy the basic structure of biofilms, and furthermore, increase the penetration and diffusion of chemicals into the deeper layer of biofilms for achieving a synergistic effect on the biofilm control.

Ultrasound-involved emerging strategies for controlling foodborne microbial biofilms

Improvement of in vitro and in situ antifungal, AFB1 inhibitory and antioxidant activity of Origanum majorana L. essential oil through nanoemulsion and recommending as novel food preservative.

Increasing antibiotic resistance continues to focus on research into the discovery of novel antimicrobial agents. Due to its antimicrobial and wound healing-promoting activity, metal nanoparticles have attracted attention for dermatological applications. This study is designed to investigate the scope and bactericidal potential of zinc ferrite nanoparticles (ZnFe2O4 NPs), and the mechanism of anti-bacterial action along with cytocompatibility, hemocompatibility, and wound healing properties. ZnFe2O4 NPs were synthesized via a modified co-precipitation method. Structure, size, morphology, and elemental compositions of ZnFe2O4 NPs were analyzed using X-ray diffraction pattern, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. In PrestoBlue and live/dead assays, ZnFe2O4 NPs exhibited dose-dependent cytotoxic effects on human dermal fibroblasts. In addition, the hemocompatibility assay revealed that the NPs do not significantly rupture red blood cells up to a dose of 1000 µg/mL. Bacterial live/dead imaging and zone of inhibition analysis demonstrated that ZnFe2O4 NPs showed dose-dependent bactericidal activities in various strains of Gram-negative and Gram-positive bacteria. Interestingly, NPs showed antimicrobial activity through multiple mechanisms, such as cell membrane damage, protein leakage, and reactive oxygen species generation, and were more effective against gram-positive bacteria. Furthermore, in vitro scratch assay revealed that ZnFe2O4 NPs improved cell migration and proliferation of cells, with noticeable shrinkage of the artificial wound model. This study indicated that ZnFe2O4 NPs have the potential to be used as a future antimicrobial and wound healing drug.

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Anti‐bacterial and wound healing‐promoting effects of zinc ferrite nanoparticles

The antifungal mechanism of essential oils against fungi remains in the shallow study. In this paper, antifungal mechanism of trans-cinnamaldehyde against Penicillium italicum was explored. Trans-cinnamaldehyde exhibited strong mycelial growth inhibition against Penicillium italicum, with minimum inhibitory concentration of 0.313 μg/mL. Conventional analytical tests showed that trans-cinnamaldehyde changed the cell membrane permeability, which led to the leakage of some materials. Meanwhile, the membrane integrity and cell wall integrity also changed. Surface-enhanced Raman spectroscopy, an ultrasensitive and fingerprint method, was served as a bran-new method to study the antifungal mechanism. Characteristic peaks of supernatant obviously changed at 734, 1244, 1330, 1338 and 1466 cm−1. The Raman intensity represented a strong correlation with results from conventional methods, which made SERS an alternative to study antifungal process. All evidences implied that trans-cinnamaldehyde exerts its antifungal capacity against Penicillium italicum via membrane damage mechanism.

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Membrane damage mechanism contributes to inhibition of trans-cinnamaldehyde on Penicillium italicum using Surface-Enhanced Raman Spectroscopy (SERS).

The effect of 10 essential oil (EO) components on biofilm formation for vegetable spoilage Erwinia carotovora and Pseudomonas fluorescens at sub-MICs were investigated. Chromobacterium violaceum CV026 (CV026) was selected as quorum sensing (QS) biosensor bacterium. The swimming, swarming, twitching motility, exopolysaccharide (EPS) production and biofilm formation were determined. All tested EO components showed QS inhibition of CV026, E. carotovora and P. fluorescens. Biofilms were inhibited by all EO components by inhibiting their motilities and EPS production. Salicylic acid and thymol showed the best inhibitory effect on biofilm formation of P. fluorescens (37.61%) and E. carotovora (47.24%) respectively. Hexanal as QS inhibitor for biofilm formation was first reported, with inhibition ratio of 25.86% and 20.18%, which was confirmed by scanning electron and fluorescence microscopy. Inhibition of biofilm formation by anti-QS EO components could be novel intervention strategy to enhance safety and quality of vegetables in the food industry.

Essential oil components inhibit biofilm formation in Erwinia carotovora and Pseudomonas fluorescens via anti-quorum sensing activity.

To control the decay of fresh vegetables or fruits after harvest and overcome higher costs using a natural agent, synergistic antifungal effects were studied in tomatoes and their main decay fungi Fusarium solani and Rhizopus stolonifer. After screening 56 groups with a checkerboard method based on 11 natural agents, only one combination of thymol and salicylic acid (S TSA ) had a synergistic effect on both fungi. Their average minimal inhibitory concentration (MIC) values decreased significantly to 0.43 fold compared with the single agents tested. Their mycelial growth was completely inhibited; the inhibition rates of spore germination exceeded 96% at 0.5, 1, and 2 MIC. The protective and therapeutic effects were found to be dose-dependent during exposure; the former was always better than the latter against both fungi at any tested concentration in wound-inoculated tomatoes, and phytotoxicity occurred only when the concentration of S TSA reached 2 MIC in naturally stored fruit. Consumer evaluation showed that the natural, non-inoculated tomatoes treated with 1 MIC and the wound-inoculated tomatoes treated with 2 MIC were both acceptable. The in vitro and in vivo results show that a combination of thymol and salicylic acid could be developed as a control measure and could reduce costs.

Jie Kong

Papers

Antifungal effects of thymol and salicylic acid on cell membrane and mitochondria of Rhizopus stolonifer and their application in postharvest preservation of tomatoes.

Membrane damage mechanism contributes to inhibition of trans-cinnamaldehyde on Penicillium italicum using Surface-Enhanced Raman Spectroscopy (SERS).

Essential oil components inhibit biofilm formation in Erwinia carotovora and Pseudomonas fluorescens via anti-quorum sensing activity.

Biocontrol of postharvest fungal decay of tomatoes with a combination of thymol and salicylic acid screening from 11 natural agents

Hexanal as a QS inhibitor of extracellular enzyme activity of Erwinia carotovora and Pseudomonas fluorescens and its application in vegetables.