Bioremediation of aflatoxin B1-contaminated maize by king oyster mushroom (Pleurotus eryngii)

Characterization and mechanism of simultaneous degradation of aflatoxin B1 and zearalenone by an edible fungus of Agrocybe cylindracea GC-Ac2

Contamination with multiple mycotoxins is a major issue for global food safety and trade. This study focused on the degradation of aflatoxin B1 (AFB1) and zearalenone (ZEN) by 8 types of edible fungi belonging to 6 species, inclulding Agaricus bisporus, Agrocybe cylindracea, Cyclocybe cylindracea, Cyclocybe aegerita, Hypsizygus marmoreus and Lentinula edodes. Among these fungi, Agrocybe cylindracea strain GC-Ac2 was shown to be the most efficient in the degradation of AFB1 and ZEN. Under optimal degradation conditions (pH 6.0 and 37.4°C for 37.9 h), the degradation rate of both AFB1 and ZEN reached over 96%. Through the analysis of functional detoxification components, it was found that the removal of AFB1 and ZEN was primarily degraded by the culture supernatant of the fungus. The culture supernatant exhibited a maximum manganese peroxidase (MnP) activity of 2.37 U/mL. Interestingly, Agrocybe cylindracea strain GC-Ac2 also showed the capability to degrade other mycotoxins in laboratory-scale mushroom substrates, including 15A-deoxynivalenol, fumonisin B1, B2, B3, T-2 toxin, ochratoxin A, and sterigmatocystin. The mechanism of degradation of these mycotoxins was speculated to be catalyzed by a complex enzyme system, which include MnP and other ligninolytic enzymes. It is worth noting that Agrocybe cylindracea can degrade multiple mycotoxins and produce MnP, which is a novel and significant discovery. These results suggest that this candidate strain and its enzyme system are expected to become valuable biomaterials for the simultaneous degradation of multiple mycotoxins.

Heat stability of Trichoderma asperelloides SKRU-01 culture filtrates: Potential applications for controlling fungal spoilage and AFB1 production in peanuts

This study aimed to examine the heat stability of culture filtrates of Trichoderma asperelloides SKRU-01 (culture filtrates SKRU-01) over a temperatures range (40-121 °C) and the effects on the antifungal activity against two aflatoxin-producing strains (Aspergillus parasiticus TISTR 3276 and A. flavus PSRDC-4), aflatoxin B1 (AFB1) degradation, and the role in mycotoxin control in peanuts. The impact of SKRU-01 culture age (2-12 day-old) on both pathogenic strains revealed that the culture age of 6-12 day-old cultures exhibited no significant difference (p > 0.05) of growth inhibition for strain TISTR 3276 (81.89-82.28 %) and 4-12 day-old cultures for strain PSRDC-4 (74.87-79.06 %). The heat-treated temperatures from 40 °C to 121 °C caused no significant (p > 0.05) reduction of mycelial growth for strain TISTR 3276 (82.61 % to 79.13 %) but significant (p < 0.05) deduction for strain PSRDC-4 (75.15 % to 59.17 %). Heat treatment of the culture filtrates SKRU-01 at 60-121 °C caused the reduction on spore germination inhibition (from about 68 % to 58.16 % for strain TISTR 3276 and 51.11 % for strain PSRDC-4). These results indicate that strain TISTR 3276 exhibited greater susceptibility to culture filtrates SKRU-01 compared to strain PSRDC-4. Furthermore, the culture filtrates SKRU-01 exhibited remarkable thermal stability at 121 °C, degrading AFB1 to 63.91 %. Application of heat-stable culture filtrates SKRU-01 in peanuts demonstrated that the reduction in fungal population and AFB1 production of both pathogenic strains depended significantly (p < 0.05) on the level of heat treatment. The non-treated and 40 °C treated culture filtrates SKRU-01 could reduce AFB1 production to lower than the Standard Aflatoxin Limitation (<20 μg/kg), ensuring food safety and mitigating the health risks associated with aflatoxin exposure.

Auricularia auricular Adsorbs Aflatoxin B1 and Ameliorates Aflatoxin B1-Induced Liver Damage in Sprague Dawley Rats

Aflatoxin B1 (AFB1), as a class I carcinogen, poses a substantial health risk to individuals. Contamination of food sources, particularly grains and nuts, with Aspergillus flavus (A. flavus) contributes to the prevalence of AFB1. The impact of global warming has spurred research into the development of AFB1 prevention technologies. While edible fungi have shown potential in detoxifying AFB1, there is a scarcity of literature on the application of Auricularia auricular (A. auricular) in this context. This study aimed to investigate the ability and underlying mechanism of A. auricular mycelia to adsorb aflatoxin B1, as well as evaluate its protective effects on the AFB1-induced liver damage in SD rats. Additionally, the effects of temperature, time, pH, and reaction ratio on the adsorption rate were examined. Combining thermodynamic and kinetic data, the adsorption process was characterized as a complex mechanism primarily driven by chemical adsorption. In SD rats, the A. auricular mycelia exhibited alleviation of AFB1-induced liver damage. The protective effects on the liver attributed to A. auricular mycelia may involve a reduction in AFB1 adsorption in the intestine, mitigation of oxidative stress, and augmentation of second-phase detoxification enzyme activity. The adsorption method for AFB1 not only ensures safety and non-toxicity, but also represents a dietary regulation strategy for achieving effective defense against AFB1.

Efficacy of the antifungal metabolites of Streptomyces philanthi RL-1-178 on aflatoxin degradation with its application to prevent aflatoxigenic fungi in stored maize grains and identification of the bioactive compound

Aflatoxin B₁ is a potent carcinogen produced by Aspergillus flavus (A. flavus) and Aspergillus. parasiticus (A. parasiticus), mainly during grain storage. The efficacy of the freeze-dried culture filtrate of Streptomyces philanthi (S. philanthi) strain RL-1-178 (DCF) on degradation of aflatoxin B₁ (AFB₁) were evaluated and its bioactive compounds were identified. The DCF at a concentration of 9.0% (w/v) completely inhibited growth and AFB₁ production of A. parasiticus TISTR 3276 and A. flavus PSRDC-4 after 7 days tested in yeast-extract sucrose (YES) medium and on stored maize grains after 28 and 14 days incubation, respectively. This indicated the more tolerance of A. parasiticus over A. flavus. The DCF and bacterial cells of S. philanthi were capable to degrade AFB₁ by 85.0% and 100% for 72 h and 8 days, respectively. This confirmed the higher efficacy of the DCF over the cells. After separation of the DCF on thin-layer chromatography (TLC) plate by bioautography bioassay, each active band was identified by liquid chromatography-quadrupole time of flight mass spectrometer (LC-Q-TOF MS/MS). The results revealed two compounds which were identified as azithromycin and an unknown based on mass ions of both ESI⁺ and ESI^- modes. The antifungal metabolites in the culture filtrate of S. philanthi were proved to degrade aflatoxin B₁. It could be concluded that the DCF may be applied to prevent the growth of the two aflatoxin-producing fungi as well as the occurrence of aflatoxin in the stored maize grains.

Recent Research on Fusarium Mycotoxins in Maize—A Review

Maize (Zea mays L.) is one of the most susceptible crops to pathogenic fungal infections, and in particular to the Fusarium species. Secondary metabolites of Fusarium spp.—mycotoxins are not only phytotoxic, but also harmful to humans and animals. They can cause acute or chronic diseases with various toxic effects. The European Union member states apply standards and legal regulations on the permissible levels of mycotoxins in food and feed. This review summarises the most recent knowledge on the occurrence of toxic secondary metabolites of Fusarium in maize, taking into account modified forms of mycotoxins, the progress in research related to the health effects of consuming food or feed contaminated with mycotoxins, and also the development of biological methods for limiting and/or eliminating the presence of the same in the food chain and in compound feed.

Characterization and mechanism of aflatoxin degradation by a novel strain of Trichoderma reesei CGMCC3.5218

Aflatoxins, which are produced mainly by Aspergillus flavus and A. parasiticus, are recognized as the most toxic mycotoxins, which are strongly carcinogenic and pose a serious threat to human and animal health. Therefore, strategies to degrade or eliminate aflatoxins in agro-products are urgently needed. We investigated 65 Trichoderma isolates belonging to 23 species for their aflatoxin B₁ (AFB₁)-degrading capabilities. Trichoderma reesei CGMCC3.5218 had the best performance, and degraded 100% of 50 ng/kg AFB₁ within 3 days and 87.6% of 10 μg/kg AFB₁ within 5 days in a liquid-medium system. CGMCC3.5218 degraded more than 85.0% of total aflatoxins (aflatoxin B₁, B₂, G₁, and G₂) at 108.2–2323.5 ng/kg in artificially and naturally contaminated peanut, maize, and feed within 7 days. Box–Behnken design and response surface methodology showed that the optimal degradation conditions for CGMCC3.5218 were pH 6.7 and 31.3°C for 5.1 days in liquid medium. Possible functional detoxification components were analyzed, indicating that the culture supernatant of CGMCC3.5218 could efficiently degrade AFB₁ (500 ng/kg) with a ratio of 91.8%, compared with 19.5 and 8.9% by intracellular components and mycelial adsorption, respectively. The aflatoxin-degrading activity of the fermentation supernatant was sensitive to proteinase K and proteinase K plus sodium dodecyl sulfonate, but was stable at high temperatures, suggesting that thermostable enzymes or proteins in the fermentation supernatant played a major role in AFB₁ degradation. Furthermore, toxicological experiments by a micronucleus assay in mouse bone marrow erythrocytes and by intraperitoneal injection and skin irritation tests in mice proved that the degradation products by CGMCC3.5218 were nontoxic. To the best of our knowledge, this is the first comprehensive study on Trichoderma aflatoxin detoxification, and the candidate strain T. reesei CGMCC3.5218 has high efficient and environment-friendly characteristics, and qualifies as a potential biological detoxifier for application in aflatoxin removal from contaminated feeds.

Accumulation of HT-2 toxin from contaminated mushroom compost by edible Agaricus bisporus

Wheat straw is commonly used as a cellulose source in mushroom compost and could be a secondary source of mycotoxin contamination in the food chain. We cultivated edible Agaricus bisporus and Pleurotus ostreatus on T-2/HT-2 artificially-contaminated mushroom compost and developed and in-house validated an UHPLC-MS/MS method for determination of T-2, HT-2, T2-triol and T2-tetraol in mushroom compost and mushroom basidiocarp. A rapid phase I metabolization of T-2 and HT-2 in mushroom compost was observed. In Agaricus bisporus, basidiocarps 8-15 µg kg^-1 accumulation of HT-2 calculated on wet weight was measured. No detectable mycotoxins were found in Pleurotus ostreatus basidiocarp.

A Systematic Review of the Efficacy of Interventions to Control Aflatoxins in the Dairy Production Chain—Feed Production and Animal Feeding Interventions

The study presents a systematic review of published scientific articles investigating the effects of interventions aiming at aflatoxin reduction at the feed production and animal feeding phases of the milk value chain in order to identify the recent scientific trends and summarize the main findings available in the literature. The review strategy was designed based on the guidance of the systematic review and knowledge synthesis methodology that is applicable in the field of food safety. The Web of Science and EBSCOhost online databases were searched with predefined algorithms. After title and abstract relevance screening and relevance confirmation with full-text screening, 67 studies remained for data extraction, which were included in the review. The most important identified groups of interventions based on their mode of action and place in the technological process are as follows: low-moisture production using preservatives, acidity regulators, adsorbents and various microbiological additives. The results of the listed publications are summarized and compared for all the identified intervention groups. The paper aimed to help feed producers, farmers and relevant stakeholders to get an overview of the most suitable aflatoxin mitigation options, which is extremely important in the near future as climate change will likely be accompanied by elevated mycotoxin levels.

Potential of Trichoderma spp. for Biocontrol of Aflatoxin-Producing Aspergillus flavus

The inhibitory action of 20 antagonistic Trichoderma isolates against the aflatoxigenic isolate A. flavus ITEM 9 (Af-9) and their efficacy in reducing aflatoxin formation in vitro were examined. Production of metabolites with inhibitory effect by the Trichoderma isolates was also investigated. Antagonistic effect against Af-9 was assessed by inhibition of radial growth of the colonies and by fungal interactions in dual confrontation tests. A total of 8 out of 20 isolates resulted in a significant growth inhibition of 3-day-old cultures of Af-9, ranging from 13% to 65%. A total of 14 isolates reduced significantly the aflatoxin B₁ (AfB₁) content of 15-day-old Af-9 cultures; 4 were ineffective, and 2 increased AfB₁. Reduction of AfB₁ content was up to 84.9% and 71.1% in 7- and 15-day-old cultures, respectively. Since the inhibition of Af-9 growth by metabolites of Trichoderma was not necessarily associated with inhibition of AfB₁ production and vice versa, we investigated the mechanism of reduction of AfB₁ content at the molecular level by examining two strains: one (T60) that reduced both growth and mycotoxin content; and the other (T44) that reduced mycotoxin content but not Af-9 growth. The expression analyses for the two regulatory genes aflR and aflS, and the structural genes aflA, aflD, aflO and aflQ of the aflatoxin biosynthesis cluster indicated that neither strain was able to downregulate the aflatoxin synthesis, leading to the conclusion that the AfB₁ content reduction by these Trichoderma strains was based on other mechanisms, such as enzyme degradation or complexation. Although further studies are envisaged to identify the metabolites involved in the biocontrol of A. flavus and prevention of aflatoxin accumulation, as well as for assessment of the efficacy under controlled and field conditions, Trichoderma spp. qualify as promising agents and possible alternative options to other biocontrol agents already in use.

Simultaneous degradation of two mycotoxins enabled by a fusion enzyme in food-grade recombinant Kluyveromyces lactis

Aflatoxin B1 (AFB1) and zearalenone (ZEN) are two predominant mycotoxins ubiquitously found in corn, peanuts, and other grains, which pose a great threat to human health. Therefore, safe and effective methods for detoxification of these mycotoxins are urgently needed. To achieve simultaneous degradation of multiple mycotoxins, a fusion enzyme ZPF1 was constructed by linking zearalenone hydrolase and manganese peroxidase with a linker peptide GGGGS. This fusion enzyme was secretory expressed successfully in the newly constructed food-grade recombinant strain Kluyveromyces lactis GG799(pKLAC1-ZPF1), and was investigated with the mycotoxins degradation efficiency in two reaction systems. Results showed that both AFB1 and ZEN can be degraded by ZPF1 in reaction system 1 (70.0 mmol/L malonic buffer with 1.0 mmol/L MnSO4, 0.1 mmol/L H2O2, 5.0 µg/mL AFB1 and ZEN, respectively) with the ratios of 46.46% and 38.76%, respectively. In reaction system 2 (50.0 mmol/L Tris-HCl, with 5.0 µg/mL AFB1 and ZEN, respectively), AFB1 cannot be degraded while ZEN can be degraded with the ratio of 35.38%. To improve the degradation efficiency of these mycotoxins, optimization of the induction and degradation conditions were fulfilled subsequently. The degradation ratios of AFB1 and ZEN by ZPF1 in reaction system 1 reached 64.11% ± 2.93% and 46.21% ± 3.17%, respectively. While in reaction system 2, ZEN was degraded by ZPF1 at a ratio of 41.45% ± 3.34%. The increases of degradation ratios for AFB1 and ZEN in reaction system 1 were 17.65% and 7.45%, respectively, while that for ZEN in reaction system 2 was 6.07%, compared with the unoptimized results.

Comparison of QuEChERS and "dilute and shoot" extraction methods for multi-mycotoxin analysis of samples from button mushroom (Agaricus bisporus) cultivation

Several components of mushroom compost (wheat straw, chicken manure) can be contaminated with mycotoxins posing food health risks to mushroom consumers. To assess the relevance of such contaminations high-throughput analytical methods are needed. In this study, two sample preparation approaches, dilute & shoot (D&S) and modified citrate buffered Quick, Easy, Cheap, Effective, Rugged, Safe (QuEChERS) were compared in terms of extraction efficiency and matrix effect in case of 13 mycotoxins in complex matrices-wheat straw, the growing media and button mushrooms (Agaricus bisporus)-of mushroom cultivation using high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). D&S method resulted in recoveries of LB medium, button mushroom and compost for ≥60% in case of all investigated mycotoxins except for DON-3G. However, using modified citrate buffered QuEChERS with 2% acidification of the extraction solvent showed the complete loss of strongly polar DON-3G and fumonisin B₁ (FB₁). The investigated matrices had suppressive effect on ionization in all target mycotoxins except for FB₁. Regarding the use of isotopologues to compensate matrix effect, even U-[¹³C₁₅]-DON and U-[¹³C₂₄]-T-2 can also be used to quantify their related metabolites in the studied matrices, using internal standard method.

Novel strategies for degradation of aflatoxins in food and feed: A review

Aflatoxins are toxic secondary metabolites mainly produced by Aspergillus fungi, posing high carcinogenic potency in humans and animals. Dietary exposure to aflatoxins is a global problem in both developed and developing countries especially where there is poor regulation of their levels in food and feed. Thus, academics have been striving over the decades to develop effective strategies for degrading aflatoxins in food and feed. These strategies are technologically diverse and based on physical, chemical, or biological principles. This review summarizes the recent progress on novel aflatoxin degradation strategies including irradiation, cold plasma, ozone, electrolyzed oxidizing water, organic acids, natural plant extracts, microorganisms and enzymes. A clear understanding of the detoxification efficiency, mechanism of action, degradation products, application potential and current limitations of these methods is presented. In addition, the development and future perspective of nanozymes in aflatoxins degradation are introduced.

Statistical optimization of cultural variables for enzymatic degradation of aflatoxin B1 by Panus neostrigosus

The aim of this study is to determine the best aflatoxin B₁ degradation conditions which was optimized using a combination of the Plackett-Burman and Box-Behnken methods with Panus neostrigosus culture filtrate. Panus neostrigosus was grown in a modified Kirk Broth medium to determine optimal degradation conditions. As a result, aflatoxin B₁ was degraded under varying culture conditions. The Plackett-Burman method was designed after sixteen different experiments with fifteen variables. The three most effective variables (Sucrose, yeast extract, wheat bran) were chosen for the Box-Behnken methodology. The aflatoxin B₁ degradation rate was 49% in just 1 h exposure to culture filtrate which was obtained under optimal growth conditions; (g-ml/L) sucrose 10, yeast extract 3, wheat bran 3, soytone 5, KH₂PO₄ 2, MgSO₄.7H₂O 0.5, CaCl₂.H₂O 0.1, ammonium tartrate 2, trace element solution 10; 28 °C of incubation temperature, medium pH 5, 7.5% inoculum rate, 125 rpm of agitation speed, and a twelve-day incubation period. The SDS-PAGE studies show that the enzyme responsible for AFB₁ degradation has 38 kDa molecular weight and has no laccase or MnP activity. To the best of our knowledge, this is the first report for AFB₁ degradation by Panus neostrigosus.

Aflatoxins: Producing-Molds, Structure, Health Issues and Incidence in Southeast Asian and Sub-Saharan African Countries

This review aims to update the main aspects of aflatoxin production, occurrence and incidence in selected countries, and associated aflatoxicosis outbreaks. Means to reduce aflatoxin incidence in crops were also presented, with an emphasis on the environmentally-friendly technology using atoxigenic strains of Aspergillus flavus. Aflatoxins are unavoidable widespread natural contaminants of foods and feeds with serious impacts on health, agricultural and livestock productivity, and food safety. They are secondary metabolites produced by Aspergillus species distributed on three main sections of the genus (section Flavi, section Ochraceorosei, and section Nidulantes). Poor economic status of a country exacerbates the risk and the extent of crop contamination due to faulty storage conditions that are usually suitable for mold growth and mycotoxin production: temperature of 22 to 29 °C and water activity of 0.90 to 0.99. This situation paralleled the prevalence of high liver cancer and the occasional acute aflatoxicosis episodes that have been associated with these regions. Risk assessment studies revealed that Southeast Asian (SEA) and Sub-Saharan African (SSA) countries remain at high risk and that, apart from the regulatory standards revision to be more restrictive, other actions to prevent or decontaminate crops are to be taken for adequate public health protection. Indeed, a review of publications on the incidence of aflatoxins in selected foods and feeds from countries whose crops are classically known for their highest contamination with aflatoxins, reveals that despite the intensive efforts made to reduce such an incidence, there has been no clear tendency, with the possible exception of South Africa, towards sustained improvements. Nonetheless, a global risk assessment of the new situation regarding crop contamination with aflatoxins by international organizations with the required expertise is suggested to appraise where we stand presently.

Degradation of Aflatoxin B1 by a Sustainable Enzymatic Extract from Spent Mushroom Substrate of Pleurotus eryngii

Ligninolytic enzymes from white-rot fungi, such as laccase (Lac) and Mn-peroxidase (MnP), are able to degrade aflatoxin B₁ (AFB1), the most harmful among the known mycotoxins. The high cost of purification of these enzymes has limited their implementation into practical technologies. Every year, tons of spent mushroom substrate (SMS) are produced as a by-product of edible mushroom cultivation, such as Pleurotus spp., and disposed at a cost for farmers. SMS may still bea source of ligninolytic enzymes useful for AFB1 degradation. The in vitro AFB1-degradative activity of an SMS crude extract (SMSE) was investigated. Results show that: (1) in SMSE, high Lac activity (4 U g⁻¹ dry matter) and low MnP activity (0.4 U g⁻¹ dry matter) were present; (2) after 1 d of incubation at 25 °C, the SMSE was able to degrade more than 50% of AFB1, whereas after 3 and 7 d of incubation, the percentage of degradation reached the values of 75% and 90%, respectively; (3) with increasing pH values, the degradation percentage increased, reaching 90% after 3 d at pH 8. Based on these results, SMS proved to be a suitable source of AFB1 degrading enzymes and the use of SMSE to detoxify AFB1 contaminated commodities appears conceivable.

Biochar and hydrochar from waste biomass promote the growth and enzyme activity of soil-resident ligninolytic fungi

Biochar (BC) and hydrochar (HC) are carbonaceous products obtained through, respectively, pyrolysis and hydrothermal carbonization processes of biomass. Both materials are multi-functional soil amendments. Ligninolytic fungi are primary decomposers of recalcitrant lignocellulosic material in nature through their extensive hyphal network and enzymes. In this work, two BC samples from red spruce pellets (BC_SP) and grapevine pruning residues (BC_GV) and two HC samples from urban pruning residues (HC_UP) and the organic fraction of solid urban wastes (HC_SU) were tested at concentrations of 0.4% and 2% (w/v) on the growth and enzyme activity of Trametes versicolor, Pleurotus ostreatus and Pleurotus eryngii. In all treatments with the lower concentration, BC and HC significantly stimulated fungal growth (up to about 90% increase for HC_SU on T. versicolor), whereas at the higher dose some inhibition was observed on T. versicolor by BC_SP and P. ostreatus by BC_SP, BC_GV and HC_UP. The two materials, especially HC, at both doses noticeably increased the activity of laccase from T. versicolor and P. eryngii, up to 21 and 13 times, respectively, for HC_UP compared to controls. The activity of manganese peroxidase from P. ostreatus was also greatly stimulated by BC and HC, especially when added at the higher concentration. The overall results obtained in this study suggest potential benefits for ligninolytic fungi from the presence of these materials in soil at adequate dose of application.

Aflatoxin B1-Adsorbing Capability of Pleurotus eryngii Mycelium: Efficiency and Modeling of the Process

Aflatoxin B₁ (AfB₁) is a carcinogenic mycotoxin that contaminates food and feed worldwide. We determined the AfB₁-adsorption capability of non-viable Pleurotus eryngii mycelium, an edible fungus, as a potential means for removal of AfB₁ from contaminated solutions. Lyophilized mycelium was produced and made enzymatically inert by sterilization at high temperatures. The material thus obtained was characterized by scanning electron microscopy with regard to the morpho-structural properties of the mycotoxin-adsorbing surfaces. The active surfaces appeared rough and sponge-like. The AfB₁-mycelium system reached equilibrium at 37°C, 30 min, and pH 5–7, conditions that are compatible with the gastro-intestinal system of animals. The system remained stable for 48 h at room temperature, at pH 3, pH 7, and pH 7.4. A thermodynamic study of the process showed that this is a spontaneous and physical adsorption process, with a maximum of 85 ± 13% of removal efficiency of AfB₁ by P. eryngii mycelium. These results suggest that biosorbent materials obtained from the mycelium of the mushroom P. eryngii could be used as a low-cost and effective feed additive for AfB₁ detoxification.