Inhibitory effect of essential oils on Aspergillus ochraceus growth and ochratoxin A production

Evaluation of the efficacy of cinnamon oil on Aspergillus flavus and Fusarium proliferatum growth and mycotoxin production on paddy and polished rice: Towards a mitigation strategy

In the present investigation, the effect of cinnamon oil (CO) (10, 30, 50 and 70 %) on the growth rate (mm/day) and aflatoxin B1 (AFB1) and fumonisin B1 (FB1) production of Aspergillus flavus (AF01) and Fusarium proliferatum (FP01) isolates, respectively was determined at optimum water activities (0.95 and 0.99 aw) and temperatures (25, 30 and 35 °C) on paddy and polished rice grains. The results showed that the growth rate, AFB1 and FB1 production of all the fungal isolates decreased with an increase in CO concentrations on both matrices. AF01 and FP01 failed to grow under all conditions on paddy at 50 % of CO concentration whereas both fungi were completely inhibited (No Growth-NG) at 70 % of CO on polished rice. Regarding mycotoxin production, 30 % of CO concentrations could inhibit AFB1 and FB1 production in both matrices (No Detection-ND). In this study, the production of mycotoxins was significantly influenced by cinnamon oil compared to the growth of both fungi. These results indicated the promising potential of CO in improving the quality of rice preservation in post-harvest; however, further investigations should be evaluated on the effects on the qualitative characteristics of grains. Especially, the prospective application of CO in rice storage in industry scales to mitigate mycotoxin contamination need also to be further researched. Moreover, collaboration between researchers, agricultural experts, and food industry should be set up to achieve effective and sustainable strategies for preserving rice.

Comprehensive Insights into Ochratoxin A: Occurrence, Analysis, and Control Strategies

Ochratoxin A (OTA) is a toxic mycotoxin produced by some mold species from genera Penicillium and Aspergillus. OTA has been detected in cereals, cereal-derived products, dried fruits, wine, grape juice, beer, tea, coffee, cocoa, nuts, spices, licorice, processed meat, cheese, and other foods. OTA can induce a wide range of health effects attributable to its toxicological properties, including teratogenicity, immunotoxicity, carcinogenicity, genotoxicity, neurotoxicity, and hepatotoxicity. OTA is not only toxic to humans but also harmful to livestock like cows, goats, and poultry. This is why the European Union and various countries regulate the maximum permitted levels of OTA in foods. This review intends to summarize all the main aspects concerning OTA, starting from the chemical structure and fungi that produce it, its presence in food, its toxicity, and methods of analysis, as well as control strategies, including both fungal development and methods of inactivation of the molecule. Finally, the review provides some ideas for future approaches aimed at reducing the OTA levels in foods.

Compositional profiling and molecular docking studies of Eucalyptus polybrachtea essential oil against mucormycosis and aspergillosis

Essential oil (EO) from Eucalyptus polybrachtea is used as complementary and traditional medicine worldwide. The present study aimed at compositional profiling of EO and molecular docking of EO's bioactive compound 1,8 cineole against fungal enzymes involved in the riboflavin synthesis pathway, namely riboflavin synthase (RS), riboflavin biosynthesis protein RibD domain-containing protein (RibD), and 3,4-dihydroxy-2-butanone 4-phosphate synthase (DBPS) as apposite sites for drug designing against aspergillosis and mucormycosis, and in vitro confirmation. The compositional profile of EO was completed by GC-FID analysis. For molecular docking, the Patchdock tool was used. The ligand-enzyme 3-D interactions were examined, and ADMET properties (absorption, distribution, metabolism, excretion, and toxicity) were calculated. GC-FID discovered the occurrence of 1,8 cineole as a major component in EO, which was subsequently used for docking analysis. The docking analysis revealed that 1,8 cineole actively bound to RS, RibD, and DBPS fungal enzymes. The results of the docking studies demonstrated that the ligand 1,8 cineole exhibited H-bond and hydrophobic interactions with RS, RibD, and DBPS fungal enzymes. 1,8 cineole obeyed Lpinsky's rule and exhibited adequate bioactivity. Wet-lab authentication was achieved by using three fungal strains: Aspergillus niger, Aspergillus oryzae, and Mucor sp. Wet lab results indicated that EO was able to inhibit fungal growth.

Effects and mechanisms of plant bioactive compounds in preventing fungal spoilage and mycotoxin contamination in postharvest fruits: A review

Spoilage and mycotoxin contamination of fruits cause significant economic losses and food safety issues. Synthetic chemical fungicide treatment as primary postharvest management has attracted increasing public concern in recent years, because it may cause negative effects on the environment and human health. Numerous bioactive compounds from plants have demonstrated excellent control effects on fruit spoilage and mycotoxin contamination. Plant bioactive compounds have been considered one of the most promising alternatives, because they are generally regarded as safe and environmentally friendly. Here, we reviewed the most recent advances in plant bioactive compounds in the prevention of fungal spoilage and mycotoxin contamination in fruits. The control effects of these compounds and the mechanisms involved were summarized, and current limitations and future perspectives were discussed.

Probabilistic risk assessment of exposure to multiple mycotoxins in consumers of packaged and unpackaged spices in Iran

The current study assessed the risk posed to Iranian consumers by oral exposure to a mixture of ten mycotoxins in 138 packaged and unpackaged spices collected from the Iran market. Concentrations of mycotoxins in samples were quantified by liquid chromatography, tandem mass spectrometry with triple quadrupole, and ion trap. Probabilistic health risks of oral exposure to these mycotoxins for Iranians were assessed under percent tolerable daily intake (TDI) and cancer risk scenarios. Mean concentrations of mycotoxins in both packaged and unpackaged spice samples showed statistically significant variation among different spice samples. Based on a Monte Carlo simulation model, at the 50th, 80th, and 95th centiles, oral consumption of the analyzed samples poses no carcinogenic risk for exposure to aflatoxin. Moreover, in both packaged and unpackaged samples, while the percent TDIs for ochratoxin A, deoxynivalenol, zearalenone, patulin, fumonisin B1, and fumonisin B2 were below 1.0 at the 50th, 80th, and 95th centiles, the value was above 1.0 for aflatoxin B1, aflatoxin B2, aflatoxin G1, and aflatoxin G2 at each of these centiles.

Antifungal effects of selected menthol and eugenol in vapors on green coffee beans during long-term storage

Nowadays, coffee (Coffea Arabica L.) is among the most significant agricultural products of the world and drinking coffee has become one of the most popular habits in the world. The main contamination of stored coffee beans is related with the mycotoxin produced by the toxigenic fungi belonging the genus Aspergillus. Fungal infection followed by mycotoxin biosynthesis in coffee results in notable financial losses. subsequent mycotoxin biosynthesis in coffee leads to major economic losses. Complications ranging from mild to severe can be caused by the mycotoxins produced by this genus. The aim of this investigation was to determine the effect of menthol and eugenol on Aspergillus parasiticus (CBS 100926^T) growth, spore germination, and their potential use as green coffee beans preservative during long-term storage (12 months). The minimum inhibitory concentrations (MICs) values of the menthol and eugenol were recorded to completely inhibit the growth of A. parasiticus in 400 μg/ml and 300 μg/ml, respectively. Both reduced spore germination by 9.33% and 5.66% at 300 μg/ml and 200 μg/ml, respectively. They showed efficacy in fumigated green coffee beans sample during the storage for up to 12 months providing an increase in the protection level of 62.5% for menthol and 73.21% for eugenol against the A. parasiticus contamination. This suggests that menthol and eugenol could be used as good alternatives for decreasing the deteriorations due to the fungal infections in green coffee beans during long-term storage.

The prevalence and concentration of ochratoxin A in meat and edible offal: A global systematic review and meta-analysis

The prevalence of ochratoxin A (OTA) in meat, edible offal, and meat products (MOP) was assessed through systematic review and meta-analysis. Four electronic databases were used to gather data from 1975 to September 15, 2022. Seventy-five articles comprising 8585 samples were identified and analyzed. The studies included in the analysis were conducted at a global level, with a predominant focus on Europe [72% (54/75)], Asia [13.33% (10/75)], Africa [13.33% (10/75)], and North America [1.33% (1/75)]. The overall prevalence of OTA in MOP was 39%. The highest and lowest prevalence percentages were recorded in Iraq (77%) and the USA (3%), respectively. Concerning food type, OTA prevalence was highest in the poultry gizzard (66%) and lowest in the cow liver (2%). The overall concentration of OTA in the MOP was 1.789 μg/kg. Poultry kidneys had the highest concentration of OTA (0.880-22.984 μg/kg), while pork had the lowest concentration (0.127-0.824 μg/kg). Conspicuous amounts of OTA contamination have been reported in fermented sausages. The lowest OTA concentration was found in Belgium (0.220 μg/kg) and the highest in Denmark (60.527μg/kg). These results can help food authorities minimize and control OTA in the MOP.

Experimental Evolution Reveals a Novel Ene Reductase That Detoxifies α,β-Unsaturated Aldehydes in Listeria monocytogenes

The plant essential oil component trans-cinnamaldehyde (t-CIN) exhibits antibacterial activity against a broad range of foodborne pathogenic bacteria, including L. monocytogenes, but its mode of action is not fully understood. In this study, several independent mutants of L. monocytogenes with increased t-CIN tolerance were obtained via experimental evolution. Whole-genome sequencing (WGS) analysis revealed single-nucleotide-variation mutations in the yhfK gene, encoding an oxidoreductase of the short-chain dehydrogenases/reductases superfamily, in each mutant. The deletion of yhfK conferred increased sensitivity to t-CIN and several other α,β-unsaturated aldehydes, including trans-2-hexenal, citral, and 4-hydroxy-2-nonenal. The t-CIN tolerance of the deletion mutant was restored via genetic complementation with yhfK. Based on a gas chromatography-mass spectrometry (GC-MS) analysis of the culture supernatants, it is proposed that YhfK is an ene reductase that converts t-CIN to 3-phenylpropanal by reducing the C=C double bond of the α,β-unsaturated aldehyde moiety. YhfK homologs are widely distributed in Bacteria, and the deletion of the corresponding homolog in Bacillus subtilis also caused increased sensitivity to t-CIN and trans-2-hexenal, suggesting that this protein may have a conserved function to protect bacteria against toxic α,β-unsaturated aldehydes in their environments. IMPORTANCE While bacterial resistance against clinically used antibiotics has been well studied, less is known about resistance against other antimicrobials, such as natural compounds that could replace traditional food preservatives. In this work, we report that the food pathogen Listeria monocytogenes can rapidly develop an elevated tolerance against t-cinnamaldehyde, a natural antimicrobial from cinnamon, by single base pair changes in the yhfK gene. The enzyme encoded by this gene is an oxidoreductase, but its substrates and precise role were hitherto unknown. We demonstrate that the enzyme reduces the double bond in t-cinnamaldehyde and thereby abolishes its antibacterial activity. Furthermore, the mutations linked to t-CIN tolerance increased bacterial sensitivity to a related compound, suggesting that they modify the substrate specificity of the enzyme. Since the family of oxidoreductases to which YhfK belongs is of great interest in the mediation of stereospecific reactions in biocatalysis, our work may also have unanticipated application potential in this field.

In Vitro and In Vivo Activity of Citral in Combination with Amphotericin B, Anidulafungin and Fluconazole against Candida auris Isolates

Candida auris is an emerging fungal pathogen responsible for hospital outbreaks of invasive candidiasis associated with high mortality. The treatment of these mycoses is a clinical challenge due to the high resistance levels of this species to current antifungal drugs, and alternative therapeutic strategies are needed. In this study, we evaluated the in vitro and in vivo activities of combinations of citral with anidulafungin, amphotericin B or fluconazole against 19 C. auris isolates. The antifungal effect of citral was in most cases similar to the effect of the antifungal drugs in monotherapy. The best combination results were obtained with anidulafungin, with synergistic and additive interactions against 7 and 11 of the 19 isolates, respectively. The combination of 0.06 μg/mL anidulafungin and 64 μg/mL citral showed the best results, with a survival rate of 63.2% in Caenorhabditis elegans infected with C. auris UPV 17-279. The combination of fluconazole with citral reduced the MIC of fluconazole from > 64 to 1-4 μg/mL against 12 isolates, and a combination of 2 μg/mL fluconazole and 64 μg/mL citral was also effective in reducing mortality in C. elegans. Amphotericin B combined with citral, although effective in vitro, did not improve the activity of each compound in vivo.

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.

Antifungal Activity of Menthol, Eugenol and Their Combination against Aspergillus ochraceus and Aspergillus niger In Vitro and in Stored Cereals

Aspergillus ochraceus and Aspergillus niger are spoilage and mycotoxin-producing fungi that can contaminate agricultural commodities and derived products. In the present study, menthol, eugenol, and their combination (mix 1:1) were tested to determine their contact and fumigation toxicity against the two fungi. Menthol, eugenol, and their mixture significantly reduced mycelial growth and spore germination at concentrations from 300 to 600 µg/mL, and the inhibitory effects showed clear dose dependence. The minimum inhibitory concentration (MIC) values against A. ochraceus were 500 µg/mL (menthol), 400 µg/mL (eugenol), and 300 µg/mL (mix 1:1), while the MIC values for A. niger were 500 µg/mL (menthol), 600 µg/mL (eugenol), and 400 µg/mL (mix 1:1). Additionally, the analyzed compounds exhibited more than 50% protection against A. ochraceus and A. niger by fumigation of stored cereal grains (maize, barley, and rice) in sealed containers. The binary mixture of menthol and eugenol showed synergistic effects against both fungi in both in vitro direct contact and stored grain fumigation trials. The results of the present study provide a scientific basis for the application of a combination of natural antifungals in food preservation.

Protection of postharvest grains from fungal spoilage by biogenic volatiles

Fungal spoilage of postharvest grains poses serious problems with respect to food safety, human health, and the economic value of grains. The protection of cereal grains from deleterious fungi is a critical aim in postharvest grain management. Considering the bulk volume of grain piles in warehouses or bins and food safety, fumigation with natural gaseous fungicides is a promising strategy to control fungal contamination on postharvest grains. Increasing research has focused on the antifungal properties of biogenic volatiles. This review summarizes the literature related to the effects of biogenic volatiles from microbes and plants on spoilage fungi on postharvest grains and highlights the underlying antifungal mechanisms. Key areas for additional research on fumigation with biogenic volatiles in postharvest grains are noted. The research described in this review supports the protective effects of biogenic volatiles against grain spoilage by fungi, providing a basis for their expanded application in the management of postharvest grains.

The Inhibitory Effect of Pseudomonas stutzeri YM6 on Aspergillus flavus Growth and Aflatoxins Production by the Production of Volatile Dimethyl Trisulfide

Aspergillus flavus and the produced aflatoxins cause great hazards to food security and human health across all countries. The control of A. flavus and aflatoxins in grains during storage is of great significance to humans. In the current study, bacteria strain YM6 isolated from sea sediment was demonstrated effective in controlling A. flavus by the production of anti-fungal volatiles. According to morphological characteristics and phylogenetic analysis, strain YM6 was identified as Pseudomonas stutzeri. YM6 can produce abundant volatile compounds which could inhibit mycelial growth and conidial germination of A. flavus. Moreover, it greatly prevented fungal infection and aflatoxin production on maize and peanuts during storage. The inhibition rate was 100%. Scanning electron microscopy further supported that the volatiles could destroy the cell structure of A. flavus and prevent conidia germination on the grain surface. Gas chromatography/mass spectrometry revealed that dimethyl trisulfide (DMTS) with a relative abundance of 13% is the most abundant fraction in the volatiles from strain YM6. The minimal inhibitory concentration of DMTS to A. flavus conidia is 200 µL/L (compound volume/airspace volume). Thus, we concluded that Pseudomonas stutzeri YM6 and the produced DMTS showed great inhibition to A. flavus, which could be considered as effective biocontrol agents in further application.

Unveiling ochratoxin a controlling and biodetoxification molecular mechanisms: Opportunities to secure foodstuffs from OTA contamination

Anarchic growth of ochratoxin A (OTA) producing fungi during crop production, prolonged storage, and processing results in OTA contamination in foodstuffs. OTA in food exacerbates the risk of health and economic problems for consumers and farmers worldwide. Although the toxic effects of OTA on human health have not been well established, comprehensive preventive and remedial measures will be essential to eliminate OTA from foodstuffs. Strict regulations, controlling OTA at pre- or post-harvest stage, and decontamination of OTA have been adopted to prevent human and animal OTA exposure. Biological control of OTA and bio-decontamination are the most promising strategies due to their safety, specificity and nutritional value. This review addresses the current understanding of OTA biodegradation mechanisms and recent developments in OTA control and bio-decontamination strategies. Additionally, this review analyses the strength and weaknesses of different OTA control methods and the contemporary approaches to enhance the efficiency of biocontrol agents. Overall, this review will support the implementation of new strategies to effectively control OTA in food sectors. Further studies on efficacy-related issues, production issues and cost-effectiveness of OTA biocontrol are to be carried out to improve the knowledge, develop improved delivery technologies and safeguard the durability of OTA biocontrol approaches.

Antifungal and antiocratoxigenic potential of Alpinia speciosa and Cymbopogon flexuosus essential oils encapsulated in poly(lactic acid) nanofibers against Aspergillus fungi

Essential oils encapsulated in a polymeric matrix can be used as an alternative method to control fungi and mycotoxins. The essential oils were extracted by hydrodistillation and characterized by gas chromatography. The nanofibers were produced from poly (acid lactic) (PLA) containing essential oils by the Solution Blow Spinning method. The antifungal and antimicotoxygenic properties were evaluated against Aspergillus ochraceus and Aspergillus westerdijkiae by the fumigation method. Terpinen-4-ol (20.23%), sabinene (20.18%), 1.8-cineole (16.69%), and γ-terpinene (11.03%) were the principal compounds present in the essential oil from Alpinia speciosa, whereas citral (97.67%) was dominant from Cymbopogon flexuosus. Microscopy images showed that the addition of essential oils caused an increase in the diameter of the nanofibers. The infrared spectroscopy results indicated the presence of essential oils in the PLA nanofibers. Differential scanning calorimetry curves also indicated the existence of interactions between the essential oils and polymeric macromolecules through their plasticizing action. The hydrophobic character of nanofibers was revealed by the contact angle technique. An antifungal effect was observed, the mycelial growths (3.25-100%) and the synthesis of ochratoxin A (25.94-100%) were inhibited by the presence of the nanofibers. The results suggest that bioactive nanofibers hold promise for application to control toxigenic fungi.

In vitro and in vivo anti-Candida activity of citral in combination with fluconazole

Background

The ability of Candida to develop biofilms on inert surfaces or living tissues favors recalcitrant and chronic candidiasis associated, in many instances, with resistance to current antifungal therapy.

Aim

The aim of this study was to evaluate the antifungal activity of citral, a phytocompound present in lemongrass essential oil, in monotherapy and combined with fluconazole against azole-resistant Candida planktonic cells and biofilms. The effect of citral combined with fluconazole was also analysed with regard to the expression of fluconazole resistance-associated genes in Candida albicans and the effectiveness of the combination therapy in a Caenorhabditis elegans model of candidiasis.

Results

Citral reduced biofilm formation at initial stages and the metabolic activity of the mature biofilm. The combination of citral with fluconazole was synergistic, with a significant increase in the survival of C. elegans infected with Candida. RNA analysis revealed a reduction of the expression of the efflux pump encoded by MDR1, leading to a greater effect of fluconazole.

Conclusion

Citral in monotherapy and in combination with fluconazole could represent an interesting therapy to treat recalcitrant Candida infections associated to biofilms.

Neurolocomotor Behavior and Oxidative Stress Markers of Thiazole and Thiazolidinedione Derivatives against Nauphoeta cinerea

Thiazolidine compounds NJ20 {(E)-2-(2-(5-bromo-2-methoxybenzylidene)hydrazinyl)-4-(4-nitrophenyl)thiazole} and NW05 [(2-(benzo (d) (1,3) dioxol-4-ylmethylene)-N-(4-bromophenyl)-thiosemicarbazone] potentiated the effect of norfloxacin in resistant bacteria; however, there are no reports on their effects on Nauphoeta cinerea in the literature. The objective of this work was to evaluate the behavioral effects and oxidative markers of NW05 and NJ20 in lobster cockroach N. cinerea. To evaluate the behavioral study, a video tracking software was used to evaluate the locomotor points and the exploratory profile of cockroaches in the horizontal and vertical regions of a new environment. The total concentration of thiol and reduced glutathione (GSH), substances reactive to thiobarbituric acid (TBARS), free iron (II) content and mitochondrial viability were determined. The antioxidant potential was evaluated by the DPPH method. Both substances induced changes in the behavior of cockroaches, showing a significant reduction in the total distance covered and in the speed. In the cell viability test (MTT), there was a significant reduction for NJ20 (1 mM). NJ20 caused a significant increase in total levels of thiol and non-protein thiol (NPSH), although it also slightly increased the content of malondialdehyde (MDA). Both compounds (NW05 and NJ20) caused a significant reduction in the content of free iron at a concentration of 10 mM. In conclusion, the compound NJ20 caused moderate neurotoxicity (1 mM), but had good antioxidant action, while NW05 did not show toxicity or significant antioxidant activity in the model organism tested. It is desirable to carry out complementary tests related to the antioxidant prospection of these same compounds, evaluating them at different concentrations.

Antifungal and physicochemical properties of Ocimum essential oil loaded in poly(lactic acid) nanofibers

Poly(lactic acid) (PLA) nanofibers containing different proportions of the essential oils from Ocimum basilicum L. and Ocimum gratissimum L. were prepared by the solution blow spinning method. The essential oils were extracted by hydrodistillation and characterized by gas chromatography. MEV, contact angle, DSC, and FTIR were used to characterize the nanofibers. The effect of bioative nanofibers on the growth of the fungus and on the production of ochratoxin A were evaluated using the fumigation test. Linalool, 1.8-cineole and camphor were the principal components of the essential oil from O. basilicum, and eugenol was the principal constituent in the oil from O. gratissimum. An increase in the average diameter of the nanofibers was observed with the addition of the essential oils. The essential oils acted as a plasticizer, resulting in a reduction in the crystallinity of the PLA. The encapsulation of essential oils in PLA nanofibers was verified by FTIR. An effective antifungal and antimicotoxygenic activity against Aspergillus ochraceus and Aspergillus westerdjikiae was observed for the bioative nanofibers. These results confirm the potential of PLA nanofibers containing the essential oils for the control of toxigenic fungi that cause the deterioration of food and are harmful to human health.

Antifungal and Antitoxigenic Effects of Selected Essential Oils in Vapors on Green Coffee Beans with Impact on Consumer Acceptability

The main objective of this study is to evaluate the effect of selected essential oils thyme chemotype linalool (Thymus zygis L.), thyme chemotype tymol (Thymus vulgaris L.), eucalyptus (Eucalyptus globulus Labill.), lavender (Lavandula angustifolia Mill.), mint (Mentha piperita L.), almond (Prunbus dulcis Mill.), cinnamon bark (Cinnamomum zeylanicum Nees), litsea (Litsea cubeba Lour. Pers), lemongrass (Cympogon citrati L. Stapf), and ginger (Zingiber officinalis Rosc.) in the vapor phase on growth, sporulation, and mycotoxins production of two Aspergillus strains (Aspergillus parasiticus CGC34 and Aspergillus ochraceus CGC87), important postharvest pathogens of green and roasted coffee beans. Moreover, the effect of the essential oils (EOs) on the sensory profile of the coffee samples treated with EOs was evaluated. The major components of tested EOs were determined by gas chromatography and mass spectrometry (GC-MS) and gas chromatography with flame ionization detector (GC-FID). The results showed that almond, cinnamon bark, lemongrass, and litsea EOs are able to significantly inhibit the growth, sporulation, and mycotoxins production by toxigenic fungi. Sensory evaluation of coffee beans treated with EOs before and after roasting showed that some EOs (except lemongrass and litsea) do not adversely affect the taste and aroma of coffee beverages. Thus, application of the vapors of almond and cinnamon EOs appears to be an effective way that could serve to protect coffee during its transport and storage from toxigenic fungi.

Inhibition of Aspergillus flavus growth and aflatoxin B1 production by natamycin

Aspergillus flavus causes huge crop losses, reduces crop quality and has adverse effects on human and animal health. A large amount of food contaminated with aflatoxin can greatly increase the risk of liver cancer. Therefore, prevention and control of aflatoxin production have aroused attention of research in various countries. Natamycin extracted from Streptomyces spp. has been widely used in production practice due to its good specificity and safety. Here, we found that natamycin could significantly inhibit fungal growth, conidia germination, ergosterol and AFB1 production by A. flavus in a dose-dependent manner. Scanning electron microscope analysis indicated that the number of conidia was decreased, the outer wall of conidia was destroyed, and the mycelia were shrivelled and tangled by natamycin. RNA-Seq data indicated that natamycin inhibited fungal growth and conidia development of A. flavus by significantly down-regulating some genes involved in ergosterol biosynthesis, such as Erg13, HMG1 and HMG2. It inhibited conidia germination by significantly down-regulating some genes related to conidia development, such as FluG and VosA. After natamycin exposure, the decreased ratio of aflS/aflR caused by the down-regulation of all the structural genes, which subsequently resulted in the suppression of AFB1 production. In conclusion, this study served to reveal the inhibitory mechanisms of natamycin on fungal growth and AFB1 biosynthesis in A. flavus and to provide solid evidence for its application in controlling AFB1 contamination.

Prevalence of fungi in fresh tomatoes and their control by chitosan and sweet orange (Citrus sinensis) peel essential oil coating

BACKGROUND

Fungal contamination is a major cause of food spoilage. There is an urgent need to find and characterize natural preservatives. This study evaluates the prevalence of fungi in tomatoes and their control by using essential oil (EO) from sweet orange peel. Essential oils were extracted from dried and fresh sweet orange peels by using n-hexane and ethanol as extraction solvents. Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) analyses were performed to identify the chemical composition of the EO. A combination of chitosan (CS) and EO was used to control the fungal decay of tomatoes inoculated with Aspergillus niger and Penicillium citrinum.

RESULTS

Tomatoes obtained from local markets and supermarkets showed a high prevalence of Aspergillus and Penicillium spp. Essential oils extracted by ethanol from dried peels showed complete inhibition of A. niger and P. citrinum and hyphal degradation at a minimum inhibitory concentration (MIC) of 100 μL mL^-1 . The combination of EO with chitosan (2%) as a coating, effectively controlled the fungal decay of tomatoes until the eighth day of storage at 25 °C.

CONCLUSION

Due to their edible nature, and their antifungal and preservative potential, EO- and CS-based coatings can be used to extend the shelf life of tomatoes and other agriculture commodities. Essential oil- and CS-based coating can be used as alternative to synthetic preservatives, which are associated with various health hazards. © 2021 Society of Chemical Industry.

Antimycotic Effects of 11 Essential Oil Components and Their Combinations on 13 Food Spoilage Yeasts and Molds

Food safety is important to reduce food spoilage microorganisms and foodborne pathogens. However, food safety is challenging, as customers' demand for natural preservatives is increasing. Essential oils (EOs) and their components (EOCs) are alternative antibacterial and antimycotic food additives. In this study, the minimal inhibitory concentrations (MIC) of 11 different EOCs against 13 food spoilage molds and yeasts were investigated via the microdilution method. Cinnamaldehyde (CA) revealed the lowest MIC for all tested strains and all EOCs (32.81-328.1 µg ml-1). However, CA is organoleptic and was therefore combined with other EOCs via the checkerboard method. Overall, 27 out of 91 combinations showed a synergistic effect, and both respective EOC concentrations could be reduced by maintaining MIC. Thereby, the combination with citral or citronellal showed promising results. The concentration-dependent effect of CA was studied in further detail on Saccharomyces cerevisiae, with CA causing delayed growth-kinetics and reduced total cell numbers. In addition, flow cytometric measurements combined with live-dead staining indicate the fungicidal effect of CA, due to decreasing total cell numbers and increasing relative amount of propidium iodide-positive cells. In this study, we demonstrated that CA is a potent candidate for the use as a natural preservative against food-relevant mold and yeasts showing fungistatic and fungicidal effects. Therefore, CA and EOC combinations with respective lower EOC concentrations reduce organoleptic reservations, which ease their application in the food industry.

Essential oils and their nanoformulations as green preservatives to boost food safety against mycotoxin contamination of food commodities: a review

Postharvest food spoilage due to fungal and mycotoxin contamination is a major challenge in tropical countries, leading to severe adverse effects on human health. Because of the negative effects of synthetic preservatives on both human health and the environment, it has been recommended that chemicals that have a botanical origin, with an eco-friendly nature and a favorable safety profile, should be used as green preservatives. Recently, the food industry and consumers have been shifting drastically towards green consumerism because of their increased concerns about health and the environment. Among different plant-based products, essential oils (EOs) and their bioactive components are strongly preferred as antimicrobial food preservatives. Despite having potent antimicrobial efficacy and preservation potential against fungal and mycotoxin contamination, essential oils and their bioactive components have limited practical applicability caused by their high volatility and their instability, implying the development of techniques to overcome the challenges associated with EO application. Essential oils and their bioactive components are promising alternatives to synthetic preservatives. To overcome challenges associated with EOs, nanotechnology has emerged as a novel technology in the food industries. Nanoencapsulation may boost the preservative potential of different essential oils by improving their solubility, stability, and targeted sustainable release. Nanoencapsulation of EOs is therefore currently being practiced to improve the stability and bioactivity of natural products. The present review has dealt extensively with the application of EOs and their nanoformulated products encapsulated in suitable polymeric matrices, so as to recommend them as novel green preservatives against foodborne molds and mycotoxin-induced deterioration of stored food commodities. © 2021 Society of Chemical Industry.

Competency of Clove and Cinnamon Essential Oil Fumigation against Toxigenic and Atoxigenic Aspergillus flavus Isolates

Aspergillus flavus is a frequent contaminant of maize grain. We isolated this fungus, determined the colony morphology and species (by internal transcribed spacer sequencing) and measured the aflatoxin content. The selected A. flavus fungi were placed into two groups, toxigenic and atoxigenic; both appeared similar morphologically, except that the atoxigenic group lacked sclerotia. An essential oil fumigation test with clove and cinnamon oils as antifungal products was performed on fungal conidial discs and fungal colonies in Petri plates. Cinnamon oil at 2.5 to 5.0 μL/plate markedly inhibited the mycelial growth from conidial discs of both strains, whereas clove oil showed less activity. The oils had different effects on fungal mycelia. The higher clove fumigation doses of 10.0 to 20.0 μL/plate controlled fungal growth, while cinnamon oil caused less inhibition. Compared with atoxigenic groups, toxigenic A. flavus responded stably. Within abnormal A. flavus hyphae, the essential oils degenerated the hyphal morphology, resulting in exfoliated flakes and shrinkage, which were related to fungal membrane injury and collapse of vacuoles and phialide. The treatments, especially those with cinnamon oil, increased the electroconductivity, which suggested a weak mycelium membrane structure. Moreover, the treatments with essential oils reduced the ergosterol content in mycelia and the aflatoxin accumulation in the culture broth. The fumigations with clove and cinnamon oils inhibited the development of both conidia and colonies of A. flavus in dose-dependent manners.

iTRAQ proteome analysis of the antifungal mechanism of citral on mycelial growth and OTA production in Aspergillus ochraceus

BACKGROUND

Aspergillus ochraceus causes food spoilage and produces mycotoxin ochratoxin A (OTA) during storage of agricultural commodities. In this study, citral was used to inhibit A. ochraceus growth and OTA accumulation, proteomic analysis was employed to verify the mechanism of citral.

RESULTS

Citral was found to significantly inhibit fungal growth and mycotoxin production in A. ochraceus. Specifically, 75, 125, 150 and 200 μL L^-1 citral suppressed mycelial growth by 33%, 46%, 50% and 100%, respectively. Additionally, 75 μL L^-1 citral inhibited OTA accumulation by 25%. Proteomic analysis was performed to elucidate the inhibitory mechanism of citral on mycelial growth and OTA production at subinhibitory concentrations (75 μL L^-1 ). Proteomics analysis identified 2646 proteins in A. ochraceus fc-1, of which 218 were differentially expressed between control and 75 μL L^-1 citral treatment samples. Differentially expressed proteins were identified by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of biological process, cellular component and molecular function terms. Potential factors affecting mycelial growth and OTA production were analysed, and OTA production was revealed to be a complex process involving many associated factors related to various processes including nutrient intake, sterol biosynthesis, ribosome biogenesis, energy metabolism, oxidative stress and amino acid metabolism. In addition, citral at 75 μL L^-1 down-regulated OTA biosynthetic genes including pks and nrps, but slightly up-regulated the global regulatory factors veA, velB and laeA.

CONCLUSION

The findings further demonstrate the potential of citral for the preservation of grains and other agricultural products, and provide new insight into its antifungal mechanisms at subinhibitory concentrations. © 2021 Society of Chemical Industry.

Inhibitory effect of allyl and benzyl isothiocyanates on ochratoxin a producing fungi in grape and maize

The purpose of this study was to evaluate the inhibitory effect of allyl-isothiocyanate (AITC) and benzyl-isothiocyanate (BITC) on fungal growth and Ochratoxin A (OTA) production by Aspergillus ochraceus, A. carbonarius and A. niger. Here, we found that spore germination and fungal growth of the three fungi were significantly inhibited when the concentration of AITC and BITC was higher than 1.25 μg/mL. The inhibitory effect of AITC or BITC on A. carbonaceus and A. ochraceus was significantly stronger than that of A. niger. Scanning electron microscopy showed that the mycelia of all three fungi were changed by AITC and BITC. Compared with A. ochraceus and A. carbonarius, the damage to A. niger was lower. For OTA production, AITC and BITC could significantly down-regulated the expression of all five OTA biosynthesis genes in A. niger and A. carbonarius. In A. ochraceus, although several OTA biosynthesis genes were up-regulated, the key PKS gene was down-regulated by AITC and BITC. Twenty-five μg/mL of AITC or BITC could reduce the infection of the three fungi on grapes with inhibition rates of 28%-36% during 14 days and prolong the shelf life of grapes. In maize, the OTA production of the three fungi was significantly reduced by 25 μg/mL of AITC and BITC with the inhibition rates 68.04%-93.49% and 65.87%-75.45%, respectively. These results suggest that AITC and BITC can be used as natural fungicides to prevent A. niger, A. carbonarius and A. ochraceus from infecting grapes and maize and control OTA contamination.

Insight into the substrate-dependent anti-aflatoxigenic effects of nanosized ZnO film: Electron transfer directed oxidative stress mechanisms

Exploring new anti-aflatoxigenic materials and their mechanisms are critical to reduce the prevalence of drug-resistant fungi and the contamination of aflatoxins. Zinc oxide nanoparticles (ZnONPs) are promising antifungal candidates but supporting substrates generally affect their antifungal activities. In this study, ZnONPs with a three-dimensional flower-like hierarchical microstructure bound to different substrates as anti-aflatoxigenic composites were prepared using a facile deposition method. It was found that ZnO nanocomposites showed the substrate-dependent anti-aflatoxigenic activities. The antifungal activities of ZnO films toward A. flavus growth and aflatoxin B₁ production decreased significantly in the order ZnO@Zn＞ZnO@Sn＞ZnO@Steel＞ZnO@Glass. The electrical conductivity of the substrate should play an important role for antifungal response. When compared with ZnO@Sn and ZnO@Steel, the conductivity value of ZnO@Zn was 2.07-fold and 14.84-fold of them, respectively. The higher the electrical conductivity of the substrate, the better the anti-aflatoxigenic efficiency of the composite. Such anti-aflatoxigenic activity was also due to ROS generation through electron transfer between fungi and the ZnO-substrate system, which could provoke the strength of intracellular oxidative stress. This mechanism was further confirmed using several assays such as hyphal morphology analysis, Zn²⁺ release, ROS evaluation, lipid peroxidation and antioxidant response. Collectively, improvement in knowledge regarding anti-aflatoxigenic performance of ZnONPs can help develop novel and effective strategies to reduce fungi growth and aflatoxin contamination in the food field.

Citronellal Exerts Its Antifungal Activity by Targeting Ergosterol Biosynthesis in Penicillium digitatum

Ergosterol (ERG) is a potential target for the development of antifungal agents against Penicillium digitatum, the pathogen of green mold in citrus fruits. This study examined the mechanism by which citronellal, a typical terpenoid of Cymbopogon nardus essential oil, acts on ergosterol to exhibit its antifungal activity against P. digitatum. We previously reported that citronellal inhibited the growth of P. digitatum with minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of 1.36 and 2.72 mg/mL, respectively. In citronellal-treated cells, the membrane integrity and ergosterol contents significantly decreased, whereas lanosterol, which serves as a precursor for ergosterol biosynthesis, massively accumulated. Addition of 150 mg/L of exogenous ergosterol decreased the inhibitory rate of citronellal, restoring the ergosterol content and hence the membrane structure to normal levels, and triggered expression of nearly all ERG genes. Based on our findings, we deduce that citronellal damages the cell membrane integrity of P. digitatum by down-regulating the ERG genes responsible for conversion of lanosterol to ergosterol, the key downregulated gene being ERG3, due to the observed accumulation of ergosta-7,22-dienol.

The AFLATOX® Project: Approaching the Development of New Generation, Natural-Based Compounds for the Containment of the Mycotoxigenic Phytopathogen Aspergillus flavus and Aflatoxin Contamination

The control of the fungal contamination on crops is considered a priority by the sanitary authorities of an increasing number of countries, and this is also due to the fact that the geographic areas interested in mycotoxin outbreaks are widening. Among the different pre- and post-harvest strategies that may be applied to prevent fungal and/or aflatoxin contamination, fungicides still play a prominent role; however, despite of countless efforts, to date the problem of food and feed contamination remains unsolved, since the essential factors that affect aflatoxins production are various and hardly to handle as a whole. In this scenario, the exploitation of bioactive natural sources to obtain new agents presenting novel mechanisms of action may represent a successful strategy to minimize, at the same time, aflatoxin contamination and the use of toxic pesticides. The Aflatox® Project was aimed at the development of new-generation inhibitors of aflatoxigenic Aspergillus spp. proliferation and toxin production, through the modification of naturally occurring molecules: a panel of 177 compounds, belonging to the thiosemicarbazones class, have been synthesized and screened for their antifungal and anti-aflatoxigenic potential. The most effective compounds, selected as the best candidates as aflatoxin containment agents, were also evaluated in terms of cytotoxicity, genotoxicity and epi-genotoxicity to exclude potential harmful effect on the human health, the plants on which fungi grow and the whole ecosystem.

Development of a Methodology for Estimating the Ergosterol in Meat Product-Borne Toxigenic Moulds to Evaluate Antifungal Agents

Antifungal agents are commonly used in the meat industry to prevent the growth of unwanted moulds, such as toxigenic ones, on dry-cured meat products. For enhancing the application of antifungals, their mode of action must be evaluated. Their effect on the mould ergosterol content is one of the most studied ones, since it is the target site of some commercialised antifungals or of those that are in development. The aim of this study was to develop a methodology for determining how the antifungal agents used in the meat industry work. A method for analysing ergosterol was firstly developed using high-performance liquid chromatography with fluorescence detection coupled to a diode array detector (HPLC-FLD/DAD). The chromatographically optimised conditions (gradient and mobile phases) allowed us to reduce the time per analysis with respect to previously published methods up to 22 min. Withing the six checked extraction methods, method 5, showing the best mean recovery values (99.51%), the shortest retention time (15.8 min), and the lowest standard deviation values (9.92) and working temperature (60 °C), was selected. The limit of detection and limit of quantification were 0.03 and 0.1 µg/mL, respectively. All the validation parameters corroborated the method's suitability. Finally, its feasibility for evaluating the effect of a commercial antifungal preparation (AP) and different herbs that are frequently added to meat products on the ergosterol content of several toxigenic moulds was studied. Differences at the strain level were obtained in the presence of AP. Moreover, the addition of herbs significantly reduced the ergosterol content in Penicillium nordicum up to 83.91%. The developed methodology is thus suitable for screening the antifungals' role in altering mould ergosterol biosynthesis before their application in real meat products.

Recent advances on the efficacy of essential oils on mycotoxin secretion and their mode of action

Essential oils, as extracted compounds from plants, are volatile and aromatic liquids which their unique aromatic compounds give each essential oil its distinctive essence. Fungi toxins can induce various adverse health effects like allergy, cancer, and immunosuppression. Moreover, fungal spoilage impacts pharmaceutical and food industries economic state. A drop in the utilization of synthetic compounds as food prophylaxis has occurred due to several factors such as hygiene agents' alerts and stricter legal regulations. Therefore, the applications of natural substances such as essential oils have increased in recent years. Oregano, cinnamon, thyme, rosemary, fennel, clove, palmarosa, and eucalyptus have been the highest employed essential oils against mycotoxigenic fungi and their mycotoxins in studies conducted in the past decade. Essential oils inhibit fungi growth and mycotoxin synthesis via diverse pathways including modified fungal growth rate and extended lag phase, disruption of cell permeability, disruption of the electron transport chain and manipulating gene expression patterns and metabolic processes. In the present review, we will investigate the implications and efficacy of essential oils in preventing the growth of mycotoxigenic fungi, eliminating mycotoxins and their mechanism of actions conducted in the last decade. HighlightsThe most investigated toxigenic genera are Aspergillus, Fusarium and Penicillium Spp.AB1, AG1, OTA and AB2 are the most frequently studied toxinsOregano, cinnamon and thyme are mostly exploited EOs on toxigenic fungi & mycotoxinsOregano, thyme & cinnamon are the most significant antifungals on toxigenic generaCinnamon, oregano & cinnamaldehyde are the fittest antimycotoxins on DON, OTA & AFB1.

A review of the methods used to determine the target site or the mechanism of action of essential oils and their components against fungi

Essential oils (EOs) are complex mixtures of compounds derived from plants that exhibit antimicrobial activity. Several studies have demonstrated their antifungal activity in food matrices or in vitro via vapor phase or direct addition. Recently, researchers are focusing on elucidating the target site or the mechanism of action of various EOs. Past research has suggested evidence of how EOs act in the fungal cells via assays assessed from cell wall alterations or gene expression modifications. However, no previous reports have summarized most methods for finding the target site of the mechanism of action for EOs. Therefore, this review presents the methods and assays used to discover the target site or the mechanism of action of EOs against fungal cells. Researchers commonly analyze the plasma membrane integrity using various techniques as well as the changes in cell morphology. Meanwhile, the quantification of the activity of the mitochondrial enzymes, ROS species, and gene expression are less assayed.

Investigation of the Antifungal and Anti-Aflatoxigenic Potential of Plant-Based Essential Oils against Aspergillus flavus in Peanuts

Aspergillus species are known to cause damage to food crops and are associated with opportunistic infections in humans. In the United States, significant losses have been reported in peanut production due to contamination caused by the Aspergillus species. This study evaluated the antifungal effect and anti-aflatoxin activity of selected plant-based essential oils (EOs) against Aspergillus flavus in contaminated peanuts, Tifguard, runner type variety. All fifteen essential oils, tested by the poisoned food technique, inhibited the growth of A. flavus at concentrations ranging between 125 and 4000 ppm. The most effective oils with total clearance of the A. flavus on agar were clove (500 ppm), thyme (1000 ppm), lemongrass, and cinnamon (2000 ppm) EOs. The gas chromatography-mass spectrometry (GC-MS) analysis of clove EO revealed eugenol (83.25%) as a major bioactive constituent. An electron microscopy study revealed that clove EO at 500 ppm caused noticeable morphological and ultrastructural alterations of the somatic and reproductive structures. Using both the ammonia vapor (AV) and coconut milk agar (CMA) methods, we not only detected the presence of an aflatoxigenic form of A. flavus in our contaminated peanuts, but we also observed that aflatoxin production was inhibited by clove EO at concentrations between 500 and 2000 ppm. In addition, we established a correlation between the concentration of clove EO and AFB1 production by reverse-phase high-performance liquid chromatography (HPLC). We demonstrate in our study that clove oil could be a promising natural fungicide for an effective bio-control, non-toxic bio-preservative, and an eco-friendly alternative to synthetic additives against A. flavus in Georgia peanuts.

Agrobiological Interactions of Essential Oils of Two Menthol Mints: Mentha piperita and Mentha arvensis

This review article discusses the active constituents and potential of two menthol mint oils, Mentha piperita (MPEO) and Mentha arvensis (MAEO), as natural sources for botanical pesticides. The biological activities of these menthol mint oils, which can be useful in agriculture, have been broadly researched, especially toward phytotoxic microorganisms. To a lesser extent, the insecticidal and herbicidal activities of mint EOs have also been studied. It is apparent that the prospect of using menthol mint oils in agriculture is increasing in popularity. A number of investigations showed that the in vitro efficacy of MPEO and MAEO, as well as that of their main constituent, menthol, is pronounced. The results of in vitro research are useful for choosing EOs for further investigations. However, it is clear that in situ experiments are crucial and should be more extensively developed. At the same time, known techniques are to be applied to this area and new methods should be worked out, aiming at the improvement of EOs’ pesticidal efficacy and cost-effectiveness, for future implementation in agricultural pest control.

Influence of nonionic and ionic surfactants on the antifungal and mycotoxin inhibitory efficacy of cinnamon oil nanoemulsions

The influence of ionic surfactants (cationic surfactant lauric arginate and anionic surfactant lysolecithin) on the physical properties, antifungal and mycotoxin inhibitory efficacy of Tween 80 stabilized cinnamon oil-in-water nanoemulsions was investigated. Nanoemulsion droplets of similar particle diameter (∼100 nm), but variable electrical characteristics, were formed by mixing 0.1 wt% ionic surfactant with 0.9 wt% Tween 80 before homogenization. The nanoemulsions were physically stable over 28 days at 23 °C. The antifungal activity (against mycelial growth and spore germination) and mycotoxin inhibitory activity of cinnamon oil nanoemulsions bearing positive, neutral, and negative charge surface was then evaluated against two chemotypes of Fusarium graminearum. In general, the cinnamon oil played a decisive role in the resulting antifungal and mycotoxin inhibitory activities. The surfactant charge had a limited impact on the antifungal mycotoxin inhibitory activities of cinnamon oil in the nanoemulsions. Both ionic surfactant-based cinnamon oil nanoemulsions showed greater activity in inhibiting mycelial growth and mycotoxin production of F. graminearum than those based on Tween 80. Treatment of mycelium with cinnamon oil nanoemulsions resulted in the loss of cytoplasm from fungal hyphae, and accounted for the antifungal action. These results have important implications for the design of essential oil based nanoemulsions as effective antifungal delivery systems in foods.

A review of cinnamaldehyde and its derivatives as antibacterial agents

There is a continuing rise in the occurrence of multidrug-resistant bacterial infections. Antibiotic resistance to currently available antibiotics has become a global health issue leading to an urgent need for alternative antibacterial strategies. There has been a renewed interest in the development of antibacterial agents from natural sources, and trans-cinnamaldehyde is an example of a naturally occurring compound that has received significant attention in recent years. Trans-Cinnamaldehyde has been shown to possess substantial antimicrobial activity, as well as an array of other medicinal properties, and represents an intriguing hit compound from which a number of derivatives have been developed. In some cases, these derivatives have been shown to possess improved activity, not only compared to trans-cinnamaldehyde but also to commonly used antibiotics. Therefore, understanding the antibacterial mechanisms of action that these compounds elicit is imperative in order to facilitate their development and the development of new antibacterial agents that could exploit similar mechanistic approaches. The purpose of this review is to provide an overview of current knowledge on the antibacterial activity and mechanisms of action of cinnamaldehyde and its derivatives, and to highlight significant contributions made in this research area. It is hoped that the findings presented in this work will aid the future development of new antibacterial agents.