Mechanism of antifungal activity of Perilla frutescens essential oil against Aspergillus flavus by transcriptomic analysis

Sanxiapeptin is an ideal preservative with a dual effect of controlling green mold and inducing systemic defense in postharvest citrus

Green mold is a common postharvest disease infected by Penicillium digitatum that causes citrus fruit decay, and severely affects fruit storage quality. This work aimed to investigate the antifungal activity of Sanxiapeptin against P. digitatum, and elucidate the possible mechanisms involved. Sanxiapeptin was capable of inhibiting spore germination, germ tube length and mycelial growth. The SYTOX green staining assay revealed that Sanxiapeptin targeted the fungal membrane, and changed the membrane permeability, leading to the leakage of cell constituents. Meanwhile, Sanxiapeptin could influence the cell wall permeability and integrity by increasing the activities of chitinase and glucanase, resulting in abnormal chitin consumption and the decrease of glucan. Intriguingly, Sanxiapeptin could effectively control postharvest decay in citrus fruits, and activate the host resistance responses by regulating the phenylpropanoid pathway. In conclusion, Sanxiapeptin exhibits multiphasic antifungal mechanisms of action to control green mold in citrus fruits, shows great potential as novel food preservatives.

Terpinen-4-ol from tea tree oil prevents Aspergillus flavus growth in postharvest wheat grain

Plant volatile organic compounds (PVOCs) have gained increasing attention for their role in preventing fungal spoilage and insect contamination in postharvest agro-products owing to their effectiveness and sustainability. In this study, the essential oil was extracted from fresh M. alternifolia (tea tree) leaves, and the fumigation vapor of tea tree oil (TTO) completely inhibited the growth of Aspergillus flavus on agar plates at a concentration of 1.714 μL/mL. Terpinen-4-ol was identified as the major component (40.76 %) of TTO volatiles analyzed using headspace gas chromatography-mass spectrometry. Terpinen-4-ol vapor completely inhibited the A. flavus growth on agar plates and 20 % moisture wheat grain at 0.556 and 1.579 μL/mL, respectively, indicating that terpinen-4-ol serves as the main antifungal constituent in TTO volatiles. The minimum inhibitory concentration of terpinen-4-ol in liquid-contact culture was 1.6 μL/mL. Terpinen-4-ol treatment caused depressed, wrinkled, and punctured mycelial morphology and destroyed the plasma membrane integrity of A. flavus. Metabolomics analysis identified significant alterations in 93 metabolites, with 79 upregulated and 14 downregulated in A. flavus mycelia exposed to 1.6 μL/mL terpinen-4-ol for 6 h, involved in multiple cellular processes including cell membrane permeability and integrity, the ABC transport system, pentose phosphate pathway, and the tricarboxylic acid cycle. Biochemical analysis and 2,7-dichlorofluorescein diacetate staining showed that terpinen-4-ol induced oxidative stress and mitochondrial dysfunction in A. flavus mycelia. This study provides new insights into the antifungal effects of the main TTO volatile compounds terpinen-4-ol on the growth of A. flavus.

Antifungal mechanisms of binary combinations of volatile organic compounds produced by lactic acid bacteria strains against Aspergillusflavus

Aspergillus flavus（A. flavus）, a common humic fungus known for its ability to infect agricultural products, served as the subject of investigation in this study. The primary objective was to assess the antifungal efficacy and underlying mechanisms of binary combinations of five volatile organic compounds (VOCs) produced by lactic acid bacteria, specifically in their inhibition of A. flavus. This assessment was conducted through a comprehensive analysis, involving biochemical characterization and transcriptomic scrutiny. The results showed that VOCs induce notable morphological abnormalities in A. flavus conidia and hyphae. Furthermore, they disrupt the integrity of the fungal cell membrane and cell wall, resulting in the leakage of intracellular contents and an increase in extracellular electrical conductivity. In terms of cellular components, VOC exposure led to an elevation in malondialdehyde content while concurrently inhibiting the levels of total lipids, ergosterol, soluble proteins, and reducing sugars. Additionally, the impact of VOCs on A. flavus energy metabolism was evident, with significant inhibition observed in the activities of key enzymes, such as Na+/K+-ATPase, malate dehydrogenase, succinate dehydrogenase, and chitinase. And they were able to inhibit aflatoxin B1 synthesis. The transcriptomic analysis offered further insights, highlighting that differentially expressed genes (DEGs) were predominantly associated with membrane functionality and enriched in pathways about carbohydrate and amino acid metabolism. Notably, DEGs linked to cellular components and energy-related mechanisms exhibited down-regulation, thereby corroborating the findings from the biochemical analyses. In summary, these results elucidate the principal antifungal mechanisms of VOCs, which encompass the disruption of cell membrane integrity and interference with carbohydrate and amino acid metabolism in A. flavus.

An innovative Pickering W/O/W nanoemulsion co-encapsulating hydrophilic lysozyme and hydrophobic Perilla leaf oil for extending shelf life of fish products

A Pickering water-in-oil-in-water nanoemulsion co-encapsulating lysozyme (LYS) and Perilla leaf oil (PO) was prepared using whey protein isolate-tannin acid conjugated nanoparticles (WPI-TA NPs) as emulsifiers, called LYS-PO-NE, and subsequently analyzed. The nano size and multiple phases was confirmed based on the results of confocal laser scanning microscope, scanning electron microscope, and droplet size analysis. LYS-PO-NE had high encapsulation efficiencies of 89.36 % (PO) and 43.91 % (LYS) and both could be released at a slow and continuous rate. The PO addition increased the droplet size, and the LYS addition delayed the release of PO. LYS-PO-NE also showed good storage, pH, thermal, and salt stability, and an effective combined bactericidal activity of LYS and PO against spoilage bacteria. Furthermore, the results of chilled salmon storage experiments indicated that LYS-PO-NE could extend the shelf life of chilled salmon to at least 6 days, demonstrating the potential in the shelf life for fish products.

Antifungal mechanism of rose, mustard, and their blended essential oils against Cladosporium allicinum isolated from Xinjiang naan and its storage application

AIMS

To reveal the inhibition mechanism of rose, mustard, and blended essential oils against Cladosporium allicinum isolated from Xinjiang naan, and investigate the effect of the three essential oils on oxidative damage and energy metabolism.

METHODS AND RESULTS

Rose and mustard essential oils significantly inhibited mycelial growth and spore viability in a dose-dependent relationship. After essential oil treatment, the cell membrane permeability was altered, and significant leakage of intracellular proteins and nucleic acids occurred. SEM observations further confirmed the disruption of cell structure. ROS, MDA, and SOD measurements indicated that essential oil treatment induced a redox imbalance in C. allicinum, leading to cell death. As for energy metabolism, essential oil treatment significantly reduced Na+K+-ATPase, Ca2+Mg2+-ATPase, MDH activity, and CA content, impairing metabolic functions. Finally, storage experiments showed that all three essential oils ensured better preservation of naan, with mustard essential oil having the best antifungal effect.

CONCLUSIONS

Rose and mustard essential oils and their blends can inhibit C. allicinum at multiple targets and pathways, destroying cell morphological structure and disrupting metabolic processes.

Fungicide potential of citronella and tea tree essential oils against tomato cultivation's phytopathogenic fungus Fusarium oxysporum f. sp. lycopersici and analysis of their chemical composition by GC/MS

Tomato is one of the most produced and consumed fruits in the world. However, it is a crop that faces several phytosanitary problems, such as fusarium wilt, caused by Fusarium oxysporum. Thus, this study aimed to evaluate citronella and melaleuca essential oils in vitro potential in the fungus F. oxysporum management. The chemical identification of the components in the essential oils was performed by gas chromatography with flame ionization and mass spectrometer detectors. The IC50 and IC90 were determined by linear regression and the percentage of inhibition of the fungus by analysis of variance. The major compounds in citronella essential oil were citronellal, Geraniol, and citronellol; in melaleuca (tea tree) oil were terpinen-4-ol and α-terpinene. Both oils promoted more significant inhibition at concentrations of 1.5 and 2.5 μL/mL, besides not presenting significant differences with commercial fungicides, confirming the high potential for using this control method in agriculture.

Antifungal effects of carvacrol, the main volatile compound in Origanum vulgare L. essential oil, against Aspergillus flavus in postharvest wheat

Plant volatile organic compounds (VOCs) with antimicrobial activity could potentially be extremely useful fumigants to prevent and control the fungal decay of agricultural products postharvest. In this study, antifungal effects of volatile compounds in essential oils extracted from Origanum vulgare L. against Aspergillus flavus growth were investigated using transcriptomic and biochemical analyses. Carvacrol was identified as the major volatile constituent of the Origanum vulgare L. essential oil, accounting for 66.01 % of the total content. The minimum inhibitory concentrations of carvacrol were 0.071 and 0.18 μL/mL in gas-phase fumigation and liquid contact, respectively. Fumigation with 0.60 μL/mL of carvacrol could completely inhibit A. flavus proliferation in wheat grains with 20 % moisture, showing its potential as a biofumigant. Scanning electron microscopy revealed that carvacrol treatment caused morphological deformation of A. flavus mycelia, and the resulting increased electrolyte leakage indicates damage to the plasma membrane. Confocal laser scanning microscopy confirmed that the carvacrol treatment caused a decrease in mitochondrial membrane potential, reactive oxygen species accumulation, and DNA damage. Transcriptome analysis revealed that differentially expressed genes were mainly associated with fatty acid degradation, autophagy, peroxisomes, the tricarboxylic acid cycle, oxidative phosphorylation, and DNA replication in A. flavus mycelia exposed to carvacrol. Biochemical analyses of hydrogen peroxide and superoxide anion content, and catalase, superoxide dismutase, and glutathione S-transferase activities showed that carvacrol induced oxidative stress in A. flavus, which agreed with the transcriptome results. In summary, this study provides an experimental basis for the use of carvacrol as a promising biofumigant for the prevention of A. flavus contamination during postharvest grain storage.

Microbially-driven alkaline regulation: Organic acid secretion behavior of Penicillium oxalicum and charge neutralization in bauxite residue

Microbially-driven alkaline neutralization in bauxite residue by functional microorganisms is a promising approach for the ecological rehabilitation on alkaline disposal areas. However, the alkali resistance and acid secretion mechanism of functional microorganisms are still unknown, which limits their application. Here, saline-alkaline resistance, acid production performance, and differentially expressed genes of Penicillium oxalicum (P. oxalicum, a functional fungus screened from a typical disposal area) were investigated and its bio-neutralization efficiency was evaluated. This fungus exhibited high tolerance to alkalinity (pH 12), and salinity (NaCl 2.0 M), and produced a large amount of oxalic acid to reduce the medium pH to 2.0. Transcriptome showed that alkali stress induced the overexpression of genes related to antioxidant and stress-resistant enzymes (GST, KatE) and glycolytic pathway rate-limiting enzymes (HK). The rate of glycolysis and other organic acid metabolism processes was increased with higher stress resistance of P. oxalicum. The integrated application of P. oxalicum and maize straw accelerated the dissolved organic carbon content and stabilized the leachate pH of bauxite residue at about 7.4. 3DEEM and BIOSEM analysis indicated that P. oxalicum maintained high activity in the residue leachate and continuously decomposed the maize straw for their metabolism. P. oxalicum showed strong alkaline resistance, biomass degradation capacity, and alkaline regulation potential, which should be beneficial for microbial-driven alkaline regulation in bauxite residue.

Essential oils: An eco-friendly alternative for controlling toxigenic fungi in cereal grains

Fungi are widely disseminated in the environment and are major food contaminants, colonizing plant tissues throughout the production chain, from preharvest to postharvest, causing diseases. As a result, grain development and seed germination are affected, reducing grain quality and nutritional value. Some fungal species can also produce mycotoxins, toxic secondary metabolites for vertebrate animals. Natural compounds, such as essential oils, have been used to control fungal diseases in cereal grains due to their antimicrobial activity that may inhibit fungal growth. These compounds have been associated with reduced mycotoxin contamination, primarily related to reducing toxin production by toxigenic fungi. However, little is known about the mechanisms of action of these compounds against mycotoxigenic fungi. In this review, we address important information on the mechanisms of action of essential oils and their antifungal and antimycotoxigenic properties, recent technological strategies for food industry applications, and the potential toxicity of essential oils.

Transcriptomic and biochemical analyses revealed antifungal mechanism of trans-anethole on Aspergillus flavus growth

Plant volatile compounds have great potential for preventing and controlling fungal spoilage in post-harvest grains. Recently, we have reported the antifungal effects of trans-anethole, the main volatile constituent of the Illicium verum fruit, on Aspergillus flavus. In this study, the inhibitory mechanisms of trans-anethole against the growth of A. flavus mycelia were investigated using transcriptomic and biochemical analyses. Biochemical and transcriptomic changes in A. flavus mycelia were evaluated after exposure to 0.2 μL/mL trans-anethole. Scanning electron microscopy showed that trans-anethole treatment resulted in the surface wrinkling of A. flavus mycelia, and calcofluor white staining confirmed that trans-anethole treatment disrupted the mycelial cell wall structure. Annexin V-fluorescein isothiocyanate/propidium iodide double staining suggested that trans-anethole induced apoptosis in A. flavus mycelia. Reduced mitochondrial membrane potential and DNA damage were observed in trans-anethole-treated A. flavus mycelia using 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl-imidacarbocyanine and 4',6-diamidino-2-phenylindole staining, respectively. 2',7'- Dichloro-dihydro-fluorescein diacetate staining and biochemical assays demonstrated that trans-anethole treatment cause the accumulation of reactive oxygen species in the A. flavus mycelia. Transcriptome results showed that 1673 genes were differentially expressed in A. flavus mycelia exposed to trans-anethole, which were mainly associated with multidrug transport, oxidative phosphorylation, citric acid cycle, ribosomes, and cyclic adenosine monophosphate signaling. We propose that trans-anethole can inhibit the growth of A. flavus mycelia by disrupting the cell wall structure, blocking the multidrug transport process, disturbing the citric acid cycle, and inducing apoptosis. This study provides new insights into the inhibitory mechanism of trans-anethole on A. flavus mycelia and will be helpful for the development of natural fungicides. KEY POINTS: • Biochemical analyses of A. flavus mycelia exposed to trans-anethole were performed • Transcriptomic changes in trans-anethole-treated A. flavus mycelia were analyzed • An inhibitory mechanism of trans-anethole on the growth of A. flavus mycelia was proposed.

The Temporal Dynamics of Sensitivity, Aflatoxin Production, and Oxidative Stress of Aspergillus flavus in Response to Cinnamaldehyde Vapor

Cinnamaldehyde (CA), a natural plant extract, possesses notable antimicrobial properties and the ability to inhibit mycotoxin synthesis. This study investigated the effects of different concentrations of gaseous CA on A. flavus and found that higher concentrations exhibited fungicidal effects, while lower concentrations exerted fungistatic effects. Although all A. flavus strains exhibited similar responses to CA vapor, the degree of response varied among them. Notably, A. flavus strains HN-1, JX-3, JX-4, and HN-8 displayed higher sensitivity. Exposure to CA vapor led to slight damage to A. flavus, induced oxidative stress, and inhibited aflatoxin B1 (AFB1) production. Upon removal of the CA vapor, the damaged A. flavus resumed growth, the oxidative stress weakened, and AFB1 production sharply increased in aflatoxin-producing strains. In the whole process, no aflatoxin was detected in aflatoxin-non-producing A. flavus. Moreover, the qRT-PCR results suggest that the recovery of A. flavus and the subsequent surge of AFB1 content following CA removal were regulated by a drug efflux pump and velvet complex proteins. In summary, these findings emphasize the significance of optimizing the targeted concentrations of antifungal EOs and provide valuable insight for their accurate application.

Efficacy of pterostilbene suppression on Aspergillus flavus growth, aflatoxin B1 biosynthesis and potential mechanisms

Aspergillus flavus, a widespread saprotrophic filamentous fungus, could colonize agricultural crops with aflatoxin contamination, which endangers food security and the agricultural economy. A safe, effective and environmentally friendly fungicide is urgently needed. Pterostilbene, a natural phytoalexin originated from Pterocarpus indicus Willd., Vaccinium spp. and Vitis vinifera L., has been reported to possess excellent antimicrobial activity. More importantly, it is quite safe and healthy. In our screening tests of plant polyphenols for the inhibition of A. flavus, we found that pterostilbene evidently inhibited mycelial growth of Aspergillus flavus (EC50 = 15.94 μg/mL) and the inhibitory effect was better than that of natamycin (EC50 = 22.01 μg/mL), which is a natural product widely used in food preservation. Therefore, we provided insights into the efficacy of pterostilbene suppression on A. flavus growth, aflatoxin B1 biosynthesis and its potential mechanisms against A. flavus in the present study. Here, pterostilbene at concentrations of 250 and 500 μg/mL could effectively inhibit the infection of A. flavus on peanuts. And the biosynthesis of the secondary metabolite aflatoxin B1 was also inhibited. The antifungal effects of pterostilbene are exerted by inducing a large amount of intracellular reactive oxygen species production to bring the cells into a state of oxidative stress, damaging cellular biomolecules such as DNA, proteins and lipids and destroying the integrity of the cell membrane. Taken together, our study strongly supported the fact that pterostilbene could be considered a safe and effective antifungal agent against A. flavus infection.

Antibacterial mechanism of vanillin against Escherichia coli O157: H7

Vanillin, a plant-derived antimicrobial volatile substance, has potential microbial control applications in the food industry. However, the effect of vanillin on the food-borne pathogen Escherichia coli (E. coli) O157:H7 has not been well studied. This study aims to explore the antibacterial mechanism of vanillin against E. coli O157:H7. The minimum inhibitory concentration (MIC) and antibacterial effect of vanillin were determined by microdilution. Scanning electron microscopy (SEM) was used to observe the damage of vanillin to the cell membrane, while cell membrane potential and the leakage of nucleic acid protein were measured to explore the effect of vanillin on the membrane system. Confocal laser scanning and intracellular adenosine triphosphate (ATP) concentration determination were utilized to investigate the effects of vanillin on the energy, life, and death of E. coli. Finally, transcriptome sequencing was conducted to investigate the gene expression differences induced by vanillin treatment. The results showed that vanillin treatment effectively controlled E. coli O157:H7 with an MIC of 2 mg/mL. After treatment, damage to the membrane system, depolarization of the membrane, and leakage of nucleic acid and protein were observed. Meanwhile, vanillin treatment caused decreased ATP content and cell death. Transcriptome analysis showed that vanillin treatment significantly affected the expression of genes involved in cell membrane formation, tricarboxylic acid (TCA) cycling pathway, and oxidative phosphorylation pathway in E. coli O157:H7. In conclusion, membrane damage and energy metabolism disruption are important mechanisms of vanillin's inhibitory effect on E. coli O157:H7. This study provides new insights into the molecular reaction mechanism of vanillin against E. coli O157:H7, highlighting its potential as an antibacterial substance for preventing E. coli contamination in the food industry.

DNA from herbs can be obtained from air and authenticated by polymerase chain reaction

DNA barcoding of herbs allows accurate species authentication. However, the DNA of herbs are often not easily PCR amplified due to co-extraction of inhibitors. Methods have been developed to improve DNA extraction to reduce contaminants. These methods usually require toxic chemical treatments or expensive commercial kits and are labor intensive. In this report, we collected the air passed from the herbs and directly amplified the DNA obtained. Results showed that DNA could be obtained, and it was PCR amplifiable. Sequencing of the amplified DNA allowed species authentication. This DNA collection method is applicable to herbs from different plant tissues. It has the advantages of reducing the use of toxic substances and more economical.

Ursolic acid, the main component of blueberry cuticular wax, inhibits Botrytis cinerea growth by damaging cell membrane integrity

Cuticular wax has been reported to play an essential role in resisting pathogens in various fruits. This study investigated the antifungal ability of the components in blueberry cuticular wax. We showed that the cuticular wax of blueberry inhibited the growth of Botrytis cinerea and ursolic acid (UA) was the key antifungal compound. UA inhibited B. cinerea growth in vitro and in vivo. Furthermore, UA increased extracellular conductivity and cellular leakage in B. cinerea, deformed the mycelial morphology, and destroyed cell ultrastructure. We also demonstrated that UA stimulated the accumulation of reactive oxygen species (ROS) and inactivated ROS scavenging enzymes. These results indicate that UA may exert antifungal effects against B. cinerea by disrupting cell membrane integrity. Thus, UA has significant potential as an agent for the control of gray mold in blueberry.

Antifungal Activity of Glucosinolate-Derived Nitriles and Their Synergistic Activity with Glucosinolate-Derived Isothiocyanates Distinguishes Various Taxa of Brassicaceae Endophytes and Soil Fungi

The glucosinolates of Brassicaceae plants are converted into bioactive isothiocyanates and other volatiles during a challenge by pathogens and other biotic stressors. However, the role of alternative downstream products with weaker potency (e.g., nitriles) is far from being fully understood. This study tested the possible synergistic antifungal interaction between various glucosinolate-derived nitriles and 2-phenylethyl isothiocyanate (PEITC) on 45 fungal strains, including endophytes from horseradish roots (Brassicaceae) and soil fungi, using an airtight system enabling the accurate study of extremely volatile antifungal agents. The median minimal inhibitory concentrations (MICs) were 1.28, 6.10, 27.00 and 49.72 mM for 1H-indole-3-acetonitrile (IAN), 3-phenylpropanenitrile (PPN), 4-(methylsulfanyl)-butanenitrile (MSBN) and 3-butenenitrile (BN, = allyl cyanide), respectively. Thus, nitriles were considerably weaker antifungal agents compared to PEITC with a median MIC of 0.04 mM. For the same nitriles, the median fractional inhibitory concentration indices (FICIs) of the combinations were 0.562, 0.531, 0.562 and 0.625, respectively. Altogether, 47.7%, 56.8%, 50.0% and 27.3% of tested fungal strains showed a synergistic antifungal activity (FICI ≤ 0.5) for the nitrile-isothiocyanate combinations, respectively. Hypocreales strains showed the least sensitivity towards the GSL decomposition products and their combinations. The mean MIC values for PEITC showed 0.0679 ± 0.0358, 0.0400 ± 0.0214, 0.0319 ± 0.0087 and 0.0178 ± 0.0171 mM for Hypocreales, Eurotiales, Glomerellales and Pleosporales, respectively. In addition, nitriles, especially IAN, also showed significant differences. For the same fungi, the median FICI values fell in the ranges of 0.61-0.67, 0.52-0.61, 0.40-0.50 and 0.48-0.67, respectively, depending on the nitrile. Our results suggest that glucosinolate-derived nitriles may enhance isothiocyanate antifungal activity and that they may play an active role in shaping the plant microbiome and contribute to the filtering of microbes by plants.

Advances in Controllable Release Essential Oil Microcapsules and Their Promising Applications

Essential oils (EOs) have emerged as natural and popular ingredients used in the preparation of safe and sustainable products because of their unique characteristics, such as antibacterial and antioxidant activity. However, due to their high volatility, poorly solubility in water, and susceptibility to degradation and oxidation, the application of EOs is greatly limited. One of the promising strategies for overcoming these restrictions is encapsulation, which involves in the entrapment of EOs inside biocompatible materials to utilize their controllable release and good bioavailability. In this review, the microencapsulation of the controllable release EOs and their applications are investigated. The focus is on the antimicrobial mechanism of various EOs on different bacteria and fungi, release mechanism of microencapsulated EOs, and preparation research progress of the controllable EOs microcapsules. In addition, their applications are introduced in relation to the food, textiles, agriculture, and medical fields.

Inhibitive effect and mechanism of cinnamaldehyde on growth and OTA production of Aspergillus niger in vitro and in dried red chilies

Mould and mycotoxin contamination is an ongoing issue in agriculture and food industry. Production by Aspergillus niger DTZ-12 in Guizhou dried red chilies was found, leading to significant economic losses. In this study, the inhibitive efficacy (Effective Concentration, EC) of cinnamaldehyde (CIN), eugenol (EUG), carvacrol (CAR), and linalool (LIN) against A. niger DTZ-12 were evaluated. CIN with the best antifungal capacity was then investigated for the comprehensive inhibitory activity against A. niger DTZ-12 including mycelia, spores, and physiological activities. Results showed that CIN can effectively retard mycelial growth, spore germination, and OTA production of A. niger DTZ-12 in vitro and in dried red chilies during storage. At physiological level, CIN can increase cell membrane permeability by reducing the ergosterol, decrease ATP content and ATPase activity, and promote the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) in cell. These results suggested that CIN displayed a great potential to be employed as a natural and effective alternative preservative during dried red chili storage.

Inhibition of Perilla frutescens Essential Oil on Pellicle Formation of Candida tropicalis and Pichia kluyveri and Its Effect on Volatile Compounds in Sichuan Pickles

Pellicle formation is the most typical characteristic of deteriorating fermented vegetable products. Perilla frutescens essential oil (PEO) is widely used as a useful natural preservative. However, few studies have addressed the antifungal activity and mechanism of PEO in pellicle formation microorganisms, and it is still unclear whether it can inhibit pellicle formation and affect its volatile compounds in Sichuan pickles. The current study showed that PEO can inhibit pellicle formation during fermentation of Sichuan pickles as it had significant antifungal activity against the pellicle formation microorganisms Candida tropicalis SH1 and Pichia kluyveri SH2. The minimum inhibitory concentration (MIC) of PEO against C. tropicalis SH1 and P. kluyveri SH2 was determined to be 0.4 μL/mL, and the minimum fungicidal concentrations (MFCs) were 1.6 μL/mL and 0.8 μL/mL, respectively. The antifungal mechanism was activated as a result of damage to the cell membrane, an increase in the cell permeability, a decrease in the mitochondrial membrane potential, and the inhibition of ATPase activity. Meanwhile, the addition of PEO to Sichuan pickles can enrich the profiles of volatile compounds during fermentation, including limonene, myrcene, 1,8-cineole, linalool, perilla ketone, heptanal, hexanal, α-thujone and β-terpineol and thus improve the overall sensory acceptability. These results indicated that PEO has the potential to be used as a novel food preservative to control pellicle formation in fermented vegetables.

Iturin A Strongly Inhibits the Growth and T-2 Toxin Synthesis of Fusarium oxysporum: A Morphological, Cellular, and Transcriptomics Study

Fusarium oxysporum (F. oxysporum) is a common contaminant of dried fish, and the T-2 synthesis by this organism in dried fish products poses a serious public health risk. In this study, we investigated the effects of iturin A, a cyclic lipopeptide produced by Bacillus subtilis, on the growth and synthesis of the T-2 toxin of F. oxysporum, and transcriptomics was conducted. Results showed that the inhibitory effect of iturin A on F. oxysporum was significantly enhanced with an increase in iturin A concentrations. More specifically, compared with the control group, all indexes in the iturin A treatment group with 50 μg/mL were decreased to 24.84 mm, 0.33 × 106 cfu/mL, and 5.86 ng/mL for the colony diameter, number of spores, and concentration of T-2 toxin, respectively. Furthermore, iturin A was proven to destroy the integrity of cell membranes and cause a significant increase in ROS at 25 μg/mL or 50 μg/mL. Transcriptomic analysis revealed that with the treatment of iturin A, the genes of the oxidation-reduction process were up-regulated, while the gene expression of mycelial growth, cell integrity, transmembrane transport, energy metabolism, and others were down-regulated. More importantly, the Tri5 gene cluster was significantly inhibited. This study provided new insights into the mechanism for the inhibitory effect of iturin A on the growth and T-2 toxin synthesis of F. oxysporum and theoretical guidance for the application of iturin A in the preservation of dried aquatic products.

Antifungal activity and mechanism of electron beam irradiation against Rhizopus oryzae

Electron beam irradiation is a physical fungicidal technique that has emerged as a potential application in China. However, its antifungal activity and mechanism against Rhizopus oryzae have not been reported. Thus, this study aimed to investigate the antifungal activity and mechanism of electron beam irradiation of R. oryzae. The antifungal activity analysis showed that the D₁₀ value and complete elimination dose of R. oryzae irradiated by electron beam were 1.73 kGy and 8.08 kGy, respectively. Electron beam irradiation has a strong inhibitory effect on the filamentous biomass of R. oryzae. To reveal the antifungal mechanism of electron beam against R. oryzae, this study analyzed the dynamic changes in the cell wall, cell membrane, and oxidative stress induced by different irradiation doses. The results showed that electron beam irradiation destroyed the cell wall structure of R. oryzae, increasing chitinase activity and decreasing chitin content. Cell membrane integrity is disrupted, increasing relative conductivity, decreasing pH values, and decreasing soluble protein content. Electron beam irradiation causes oxidative stress in cells, increasing H₂O₂ content, decreasing antisuperoxide anion activity, decreasing DPPH free radical scavenging activity, and inhibiting defense enzyme (CAT and SOD) activity. This phenomenon indicates that electron beams can cause structural damage to and metabolic dysfunction of cells and disorders of redox homeostasis, which may be the main cause of growth inhibition and cell death in R. oryzae.

Encapsulation of Cymbopogon khasiana × Cymbopogon pendulus Essential Oil (CKP-25) in Chitosan Nanoemulsion as a Green and Novel Strategy for Mitigation of Fungal Association and Aflatoxin B1 Contamination in Food System

The present study deals with the encapsulation of Cymbopogon khasiana × Cymbopogon pendulus essential oil (CKP-25-EO) into a chitosan nanoemulsion and efficacy assessment for inhibition of fungal inhabitation and aflatoxin B₁ (AFB₁) contamination in Syzygium cumini seeds with emphasis on cellular and molecular mechanism of action. DLS, AFM, SEM, FTIR, and XRD analyses revealed the encapsulation of CKP-25-EO in chitosan with controlled delivery. The CKP-25-Ne displayed enhanced antifungal (0.08 µL/mL), antiaflatoxigenic (0.07 µL/mL), and antioxidant activities (IC_{50 DPPH} = 6.94 µL/mL, IC_{50 ABTS} = 5.40 µL/mL) in comparison to the free EO. Impediment in cellular ergosterol, methylglyoxal biosynthesis, and in silico molecular modeling of CKP-25-Ne validated the cellular and molecular mechanism of antifungal and antiaflatoxigenic activity. The CKP-25-Ne showed in situ efficacy for inhibition of lipid peroxidation and AFB₁ secretion in stored S. cumini seeds without altering the sensory profile. Moreover, the higher mammalian safety profile strengthens the application of CKP-25-Ne as a safe green nano-preservative against fungal association, and hazardous AFB₁ contamination in food, agriculture, and pharmaceutical industries.

Temperature controlled microcapsule loaded with Perilla essential oil and its application in preservation of peaches

In this study, Perilla frutescens essential oil (PEO) loaded microcapsules (PEOM) were successfully prepared and their thermal stability, temperature-responsive releasing effect, antioxidant activity, antibacterial activity, and preservation of peach were systematically investigated. PEOM showed excellent encapsulation efficiency (91.5%) with a core-shell ratio of 1.4:1 and exhibited high thermal stability, indicating that PEOM could effectively maintain PEO release rate. In vitro assays indicated that the optimal kinetic model for PEO release fitted well with first order with a diffusion mechanism. A high level of antioxidant and antibacterial activity of PEOM was maintained. In addition, owing to its sustained release, PEOM could prolong the shelf life of peaches significantly. Therefore, PEOM has potential application and development prospects in the field of food preservation.

Antifungal mechanisms of volatile organic compounds produced by Pseudomonas fluorescens ZX as biological fumigants against Botrytis cinerea

To explore the antifungal mechanisms of volatile organic compounds (VOCs) produced by Pseudomonas fluorescens ZX against Botrytis cinerea, biochemical analyses and transcriptomic techniques were employed in this work. The results showed that P. fluorescens ZX-producing VOCs can increase the cell membrane permeability of B. cinerea and disrupt cell membrane integrity, resulting in leakage of the pathogen's cellular contents, inhibition of ergosterol biosynthesis (about 76%), and an increase in malondialdehyde (MDA) content. Additionally, for B. cinerea respiration, P. fluorescens ZX-producing VOCs (1 × 10⁹ CFU /mL) significantly inhibited the activities of ATPase (55.7%), malate dehydrogenase (MDH) (33.1%), and succinate dehydrogenase (SDH) (57.9%), seriously interfering with energy metabolism and causing accumulation of reactive oxygen species (ROS). Furthermore, transcriptome analysis of B. cinerea following exposure to VOCs revealed 4590 differentially expressed genes (DEGs) (1388 upregulated, 3202 downregulated). Through GO analysis, these DEGs were determined to be enriched in intrinsic components of membrane, integral components of membrane, and membrane parts, while KEGG analysis indicated that they were enriched in many amino acid metabolism pathways. Significantly, the DEGs related to ergosterol biosynthesis, ATPase, mitochondrial respiratory chain, malate dehydrogenase, and cell membrane showed down-regulation, corroborating the biochemical analyses. Taken together, these results suggest that the antifungal activity of P. fluorescens ZX-producing VOCs against B. cinerea occurs primary mechanisms: causing significant damage to the cell membrane, negatively affecting respiration, and interfering with amino acid metabolism.

Transcriptomic and metabolomic investigation of molecular inactivation mechanisms in Escherichia coli triggered by graphene quantum dots

Graphene quantum dots (GQDs), a novel broad-spectrum antibacterial agent, are considered potential candidates in the field of biomedical and food safety due to their outstanding antimicrobial properties and excellent biocompatibility. To uncover the molecular regulatory mechanisms underlying the phenotypes, the overall regulation of genes and metabolites in Escherichia coli (E. coli) after GQDs stimulation was investigated by RNA-sequencing and LC-MS. Gene transcription and metabolite expression related to a series of crucial biomolecular processes were influenced by the GQDs stimulation, including biofilm formation, bacterial secretion system, sulfur metabolism and nitrogen metabolism, etc. This study could provide profound insights into the GQDs stress response in E. coli, which would be useful for the development and application of GQDs in food safety.

Chemical Composition and Antifungal Activity of Zanthoxylum armatum Fruit Essential Oil against Phytophthora capsici

Pathogenic plant oomycetes cause devastating damage to fruits and vegetables worldwide. Plant essential oils (EOs) are known to be promising candidates for the development of fungicides. In this study, we isolated twelve EOs from Tetradium ruticarpum, Tetradium daniellii, Tetradium fraxinifolium, Zanthoxylum armatum, Ruta graveolens, and Citrus medica leaves and fruits. We then investigated their chemical composition and antifungal activity against phytopathogenic oomycetes. Our results demonstrated that Z. armatum fruit essential oil (ZFO) in particular substantially inhibited the mycelial growth of Phytophthora capsici. Similarly, ZFO also strongly suppressed spore production and germination of P. capsici, and the application of ZFO significantly reduced disease symptoms caused by P. capsici in pepper. Furthermore, results from microscopic and biochemical studies indicated that ZFO damaged the ultrastructure and destroyed the membrane integrity of P. capsici, leading to the leakage of the cellular contents and ultimately causing cell death. It was concluded that ZFO could enhance the activities of defense-related enzymes in pepper fruits, which may also be responsible for the inhibition of phytophthora disease. Moreover, linalool and D-limonene were proven to be the primary effective components of ZFO. Our results collectively indicate that ZFO could be a potential candidate for the management of disease caused by P. capsici.

Antifungal Activity of Essential Oil and Plant-Derived Natural Compounds against Aspergillus flavus

Aspergillus flavus is a facultative parasite that contaminates several important food crops at both the pre- and post-harvest stages. Moreover, it is an opportunistic animal and human pathogen that causes aspergillosis diseases. A. flavus also produces the polyketide-derived carcinogenic and mutagenic secondary metabolite aflatoxin, which negatively impacts global food security and threatens human and livestock health. Recently, plant-derived natural compounds and essential oils (EOs) have shown great potential in combatting A. flavus spoilage and aflatoxin contamination. In this review, the in situ antifungal and antiaflatoxigenic properties of EOs are discussed. The mechanisms through which EOs affect A. flavus growth and aflatoxin biosynthesis are then reviewed. Indeed, several involve physical, chemical, or biochemical changes to the cell wall, cell membrane, mitochondria, and related metabolic enzymes and genes. Finally, the future perspectives towards the application of plant-derived natural compounds and EOs in food protection and novel antifungal agent development are discussed. The present review highlights the great potential of plant-derived natural compounds and EOs to protect agricultural commodities and food items from A. flavus spoilage and aflatoxin contamination, along with reducing the threat of aspergillosis diseases.

Preparation and characterization of Perilla essential oil composite microcapsule based on the complex coacervation and interface polymerization

In this paper, we prepared a novel double-layer Perilla essential oil composite membrane microcapsule (PEOCM) by the composite methods of complex coacervation and interface polymerization. The particle size distribution, morphology, pressure resistance, thermal stability, and elemental proportions of the microcapsule shell of the obtained microcapsules were characterized by laser particle size analyzer, scanning electron microscopy (SEM), dynamic rheometer, thermogravimetric analysis (TGA), and energy spectrometer. In order to further examine the application effect of the PEOCM, we carried out a fresh-keeping experiment on nectarines. The results showed that the average volume diameter of the microcapsules was 226.9 µm, with a completely spherical shape and a slight depression on the surface and had good pressure resistance and thermal stability. The results also demonstrated that microencapsulation does not change the composition of Perilla essential oil, and the polyurea membrane with amide structure (-NH-CO-NH-) was formed successfully. Furthermore, the total soluble solids content and peroxidase activity of nectarines indicated that the PEOCM can be a preservative of food. PRACTICAL APPLICATION: We prepared a double-layer Perilla essential oil composite membrane microcapsule by the composite methods of complex coacervation and interface polymerization. The encapsulation conditions of the microcapsules were optimized, the structure of the microcapsule was characterized, and the fresh-keeping effects of the microcapsule on nectarine were studied. The results showed that microcapsules had a completely spherical shape and a slight depression on the surface and had good pressure resistance, good thermal stability, and good fresh-keeping ability. The above characteristics indicated that the double-layer microcapsules have good application prospect and plays an important role in food fresh-keeping and the preservation of essential oils.

Antifungal mechanism of essential oil against foodborne fungi and its application in the preservation of baked food

Baked food is one of the most important staple foods in people's life, but its shelf life is limited. In addition, the spoilage of baked food caused by microbial deterioration will not only cause huge economic losses, but also pose a serious threat to human health. At present, due to the improvement of consumers' health awareness, the use of chemical preservatives has been gradually restricted. Compared with other types of synthetic preservatives, essential oils are becoming more and more popular because they are in line with the current development trend of "green," "safety" and "health" of food additives. Therefore, in this paper, we first summarized the main factors affecting the fungal contamination of baked food. Then analyzed the antifungal activity and mechanism of essential oil. Finally, we comprehensively summarized the application strategy of essential oil in the preservation of baked food. This review is of great significance for fully understanding the antifungal mechanism of essential oils and promoting the application of essential oils in the preservation of baked food.

Mechanisms underlying the inhibitory effects of linalool on Aspergillus flavus spore germination

Biogenic volatile organic compounds hold remarkable potential for controlling fungal decay in agro- and food products. Recently, we reported that linalool, the major volatile component of the Zanthoxylum schinifolium pericarp, showed great potential as a biofumigant to control Aspergillus flavus growth in postharvest grains. In this study, the inhibitory effects of linalool on A. flavus growth in stored grains and its underlying mechanism were investigated through transcriptomic and biochemical analyses. Linalool vapor at 800 μL/L can effectively prevent A. flavus growth in 22% moisture wheat grains. Linalool at 2 μL/mL completely inhibited the germination of A. flavus spores, and 10 μL/mL caused spore death. Scanning electron microscopy revealed that linalool treatment caused wrinkling and spore breakage. Transcriptomics showed that 3806 genes were significantly differentially expressed in A. flavus spores exposed to 2 μL/mL linalool, predominantly showing enrichment regarding the ribosome, DNA replication, glutathione metabolism, peroxisome, and MAPK signaling pathways. Flow cytometry showed that linalool treatment caused hyperpolarization of mitochondrial membrane potential. 4,6-Diamidino-2-phenylindole staining indicated that linalool caused DNA fragmentation in A. flavus spores, and monodansylcadaverine staining confirmed that linalool induced autophagy in A. flavus spores. We thus propose that linalool can damage the plasma membrane, cause mitochondrial dysfunction and DNA damage, and induce autophagy in A. flavus spores. These findings considerably improve our understanding of the mechanisms underlying the inhibitory effects of linalool on A. flavus, which is crucial regarding the development of applications to prevent postharvest grain spoilage due to A. flavus infestations. KEY POINTS: • The inhibitory potency of linalool on A. flavus spore germination was determined. • Transcriptomic analyses were performed to identify differentially expressed genes of A. flavus exposed to linalool. • A functional mechanism underlying the inhibitory effects of linalool on A. flavus spore germination is proposed.

Antifungal Activity of Polymethoxylated Flavonoids (PMFs)-Loaded Citral Nanoemulsion against Penicillium italicum by Causing Cell Membrane Damage

A major citrus postharvest pathogen, Penicillium italicum (P. italicum), causes substantial economic losses in citrus. In this study, a citral nanoemulsion containing polymethoxylated flavonoids (PMFs), the antimicrobial compounds from citrus, was prepared. The antifungal activity and potential antifungal mechanisms of the nanoemulsion against P. italicum were evaluated. The results showed that the growth of P. italicum was effectively inhibited by the nanoemulsion, with a minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of 62.5 and 250 mg L−1, respectively. The nanoemulsion significantly inhibited spore germination and mycelial growth, and it altered the morphology of P. italicum. In addition, the permeability of the cell membrane increased with increasing nanoemulsion concentrations, as evidenced by a rapid rise in extracellular electric conductivity and stronger red fluorescence from mycelia (propidium iodide staining). Compared with the control, the nanoemulsion treatment induced a decrease in total lipid and ergosterol contents in P. italicum cells by 64.61% and 60.58%, respectively, demonstrating that membrane integrity had been disrupted. The results indicated that the PMFs-loaded nanoemulsion exerted antifungal activity against P. italicum by disrupting cell membrane integrity and permeability; such a nanoemulsion may be used as a potential fungicide substitute for preservation in citrus fruits.

Transcriptomics analyses and biochemical characterization of Aspergillus flavus spores exposed to 1-nonanol

The exploitation of plant volatile organic compounds as biofumigants to control postharvest decaying of agro-products has received considerable research attention. Our previous study reported that 1-nonanol, the main constituent of cereal volatiles, can inhibit Aspergillus flavus growth and has the potential as a biofumigant to control the fungal spoilage of cereal grains. However, the antifungal mechanism of 1-nonanol against A. flavus is still unclear at the molecular level. In this study, the minimum inhibitory concentration and minimum fungicidal concentration of 1-nonanol against A. flavus spores were 2 and 4 μL/mL, respectively. Scanning electron microscopy revealed that the 1-nonanol can distort the morphology of A. flavus spore. Annexin V-FITC/PI double staining showed that 1-nonanol induced phosphatidylserine eversion and increased membrane permeability of A. flavus spores. Transcriptional profile analysis showed that 1-nonanol treatment mainly affected the expression of genes related to membrane damage, oxidative phosphorylation, blockage of DNA replication, and autophagy in A. flavus spores. Flow cytometry analysis showed that 1-nonanol treatment caused hyperpolarization of mitochondrial membrane potential and accumulation of reactive oxygen species in A. flavus spores. 4',6-diamidino-2-phenylindole staining showed that treatment with 1-nonanol destroyed the DNA. Biochemical analysis results confirmed that 1-nonanol exerted destructive effects on A. flavus spores by decreasing intracellular adenosine triphosphate content, reducing mitochondrial ATPase activity, accumulating hydrogen peroxide and superoxide anions, and increasing catalase and superoxide dismutase enzyme activities. This study provides new insights into the antifungal mechanisms of 1-nonanol against A. flavus. KEY POINTS: • 1-Nonanol treatment resulted in abnormal morphology of A. flavus spores. • 1-Nonanol affects the expression of key growth-related genes of A. flavus. • The apoptosis of A. favus spores were induced after exposed to 1-nonanol.

Antifungal and Antiaflatoxinogenic Effects of Cymbopogon citratus, Cymbopogon nardus, and Cymbopogon schoenanthus Essential Oils Alone and in Combination

The antifungal and antiaflatoxinogenic activities of the essential oils (EOs) from the leaves of Cymbopogon schoenanthus, Cymbopogon citratus, Cymbopogon nardus, and their pair combinations were investigated. Antifungal susceptibility and the efficacy of paired combinations of EOs were assessed using agar microdilution and checkerboard methods, respectively. Identification and quantification of chemical components of the EOs were carried out by gas chromatography-mass spectrometry and gas chromatography-flame ionization detector (GC-MS and GC-FID), respectively. Aflatoxins were separated and identified by High-Performance Liquid Chromatography (HPLC) and then quantified by spectrofluorescence. The EO of C. nardus exhibited the highest inhibitory activity against Aspergillus flavus and Aspergillus parasiticus. The combination of C. citratus and C. nardus and that of C. nardus and C. schoenanthus exhibited a synergistic effect against Aspergillus flavus and Aspergillus, respectively. Both C. citratus and C. schoenanthus EOs totally inhibited the synthesis of aflatoxin B1 at 1 µL/mL. C. citratus blocked the production of aflatoxins B2 and G2 at 0.5 µL/mL. Both C. citratus and C. schoenanthus totally hampered the production of the aflatoxin G1 at 0.75 µL/mL. The combination of C. citratus and C. schoenanthus completely inhibited the production of the four aflatoxins. The study shows that the combinations can be used to improve their antifungal and antiaflatoxinogenic activities.

Biocontrol Potential of Essential Oils in Organic Horticulture Systems: From Farm to Fork

In recent decades, increasing attention has been paid to food safety and organic horticulture. Thus, people are looking for natural products to manage plant diseases, pests, and weeds. Essential oils (EOs) or EO-based products are potentially promising candidates for biocontrol agents due to their safe, bioactive, biodegradable, ecologically, and economically viable properties. Born of necessity or commercial interest to satisfy market demand for natural products, this emerging technology is highly anticipated, but its application has been limited without the benefit of a thorough analysis of the scientific evidence on efficacy, scope, and mechanism of action. This review covers the uses of EOs as broad-spectrum biocontrol agents in both preharvest and postharvest systems. The known functions of EOs in suppressing fungi, bacteria, viruses, pests, and weeds are briefly summarized. Related results and possible modes of action from recent research are listed. The weaknesses of applying EOs are also discussed, such as high volatility and low stability, low water solubility, strong influence on organoleptic properties, and phytotoxic effects. Therefore, EO formulations and methods of incorporation to enhance the strengths and compensate for the shortages are outlined. This review also concludes with research directions needed to better understand and fully evaluate EOs and provides an outlook on the prospects for future applications of EOs in organic horticulture production.