Interaction of water activity and temperature on the growth, gene expression and aflatoxin production by Aspergillus flavus on paddy and polished rice

Development and validation of a DLLME-HPLC-FLD method for determination of aflatoxins in Chrysanthemum morifolium based on quality by design principles

INTRODUCTION

Aflatoxins, potent carcinogens produced by Aspergillus species, present significant health risks and commonly contaminate herbal products such as Chrysanthemum morifolium. Detecting these toxins in C. morifolium proves challenging due to the complex nature of the herbal matrix and the fluctuating levels of toxins found in different samples.

OBJECTIVES

This study aimed to develop and optimize a novel method for the detection of aflatoxins in C. morifolium using dispersive liquid-liquid microextraction combined with high-performance liquid chromatography-fluorescence detection based on quality by design principles.

METHODOLOGY

The method involved determining critical method attributes and parameters through the Plackett-Burman design, followed by optimization using the Box-Behnken design. Monte Carlo simulation was employed to establish a design space, which was experimentally verified. Method validation was performed to confirm accuracy, precision, and stability.

RESULTS

The developed method exhibited excellent linearity (R2 > 0.9991) for aflatoxins B1, B2, G1, and G2 across a range of concentrations, with recovery rates between 85.52% and 102.01%. The validated method effectively quantified aflatoxins in C. morifolium under different storage conditions, highlighting the impact of temperature and storage time on aflatoxin production.

CONCLUSION

This study successfully established a reliable and effective method for the detection of aflatoxins in C. morifolium, highlighting the importance of strict storage conditions to reduce aflatoxin contamination. Using a quality by design framework, the method demonstrated robustness and high analytical performance, making it suitable for routine quality control of herbal products.

Aspergillus flavus and aflatoxins control in long-term storage of food ingredients of Puerh tea, peanut and polished rice

Aflatoxins are a group of high toxic mycotoxins in food chain. Recent studies showed that aflatoxins might contaminate post-fermented tea, but the result remains controversial. Here, Aspgergillus flavus growth and aflatoxin production were characterized in Puerh tea, peanut and polished rice at different initial water activity (aw) values for long-term storage. As a result, food initial aw value was the critical factor for A. flavus growth and aflatoxin production, and A. flavus almost not grew on foods at aw value lower than 0.8. A. flavus grew best in peanut, followed by rice, but growth on Puerh tea was limited. A. flavus growth was inhibited significantly by adding tea to Potato Dextrose Agar (PDA). Accordingly, aflatoxins produced dramatically in peanut, followed by rice at the first 90 days storage. However, aflatoxin neither produced in Puerh tea nor on tea modified PDA, indicating tea components inhibited A. flavus growth and aflatoxins synthesis.

Aflatoxins in cereal based products-an overview of occurrence, detection and health implication

Aflatoxins are naturally produced toxins by specific molds, namely Aspergillus flavus and Aspergillus parasiticus. These toxins can be found in various agricultural products, including crops like maize, peanuts, cottonseed, and tree nuts. They have the potential to contaminate the food supply during different stages of production, processing, and storage. Aflatoxin is a very poisonous substance that has been linked to adverse health effects in both humans and animals. It is essential to detect and monitor aflatoxins to ensure the safety of food. Efficient and precise analytical techniques, such as chromatography and immunoassays, have been used to accurately measure the levels of aflatoxins in different substances. Regulatory bodies and worldwide associations have determined maximum permissible limits for aflatoxins in food and nourishment products to protect the well-being of the general public. Effectively addressing aflatoxin contamination necessitates a comprehensive approach that encompasses various strategies in agriculture, post-harvest practices, and regulatory measures. Continuous research and collaborative endeavors are crucial in order to minimize aflatoxin exposure and mitigate the associated risks. This review offers a comprehensive examination of the presence, health consequences, and elimination techniques associated with aflatoxins.

The Effects of Kernel Type (Inshell, Shelled and Split Almonds) on the Growth and Aflatoxin Production of A. flavus Under Different Combinations of Water Activity and Temperature

Almonds are susceptible to infestation by Aspergillus flavus, an aflatoxin-producing fungus. The objective of this study was to investigate the effects of kernel type (inshell, shelled and split almonds) on the ability of A. flavus to grow and produce aflatoxins at different combinations of temperature (20, 27 and 35 °C), water activity (0.85, 0.92, 0.95 and 0.98 aw) and incubation period (10, 20 and 30 days). There was no fungal growth at 0.85 aw on any of the kernel types. At 0.92 aw, only the split kernels supported growth and aflatoxin synthesis. The fungus was able to grow and produce aflatoxins on all three kernels at 0.95-0.98 aw and 20-35 °C. At 0.98 aw, high total aflatoxin concentrations (>300 µg/kg) were found on the shelled and split kernels at all temperatures. On the inshell nuts, the fungus produced up to 372 µg/kg of total aflatoxins at 0.98 aw and 27 °C. Regression analysis showed that significantly higher levels of aflatoxins were produced at 27 °C (as compared to at 20 and 35 °C) on shelled and split almonds. Incubation time was also a significant predictor of aflatoxin accumulation. The results of this study indicated that shipping almonds below 0.85 aw and reducing storage time would significantly decrease the risk of infestation and aflatoxin production by A. flavus.

Aflatoxins in the rice production chain: A review on prevalence, detection, and decontamination strategies

Rice (Oryza sativa L.) is one of the most consumed cereals that along with several important nutritional constituents typically provide more than 21% of the caloric requirements of human beings. Aflatoxins (AFs) are toxic secondary metabolites of several Aspergillus species that are prevalent in cereals, including rice. This review provides a comprehensive overview on production factors, prevalence, regulations, detection methods, and decontamination strategies for AFs in the rice production chain. The prevalence of AFs in rice is more prominent in African and Asian than in European countries. Developed nations have more stringent regulations for AFs in rice than in the developing world. The contamination level of AFs in the rice varied at different stages of rice production chain and is affected by production practices, environmental conditions comprising temperature, humidity, moisture, and water activity as well as milling operations such as de-husking, parboiling, and polishing. A range of methods including chromatographic techniques, immunochemical methods, and spectrophotometric methods have been developed, and used for monitoring AFs in rice. Chromatographic methods are the most used methods of AFs detection followed by immunochemical techniques. AFs decontamination strategies adopted worldwide involve various physical, chemical, and biological strategies, and even using plant materials. In conclusion, adopting good agricultural practices, implementing efficient AFs detection methods, and developing innovative aflatoxin decontamination strategies are imperative to ensure the safety and quality of rice for consumers.

Mycotoxins in grains (products), Gansu province, China and risk assessment

This study aimed to estimate the dietary exposure towards mycotoxins of residents in Gansu province, China, from 2014-2020 through surveillance data on mycotoxins in grains and grain products. Fumonisin B1 (FB1), Deoxynivalenol (DON), 3- and 15-Acetyl-deoxynivalenol (3-ADON and 15-ADON), Tentoxin (TEN), Tenuazonic acid (TeA) and Zearalenone (ZEN) in 863 grains and grain products were detected by HPLC-MS and UPLC-MS. DON was the most detected mycotoxin of all samples. For women, the average dietary exposure to DON was 1.49 μg/kg bw/day, with 55.8% of the individuals eating dried noodles exceeding tolerable daily intake. The hazard quotient values were 1.24-12.60, so greater than 1 for DON at the average, 90th percentile, 95th percentile, and maximum levels: 44.6% of the HQ values for men and 45.7% for women were greater than 1.

Glass bead system to study mycotoxin production of Aspergillus spp. on corn and rice starches

Mycotoxin production by aflatoxin B1 (AFB1) -producing Aspergillus flavus Zt41 and sterigmatocystin (ST) -hyperproducer Aspergillus creber 2663 mold strains on corn and rice starch, both of high purity and nearly identical amylose-amylopectin composition, as the only source of carbon, was studied. Scanning electron microscopy revealed average starch particle sizes of 4.54 ± 0.635 µm and 10.9 ± 2.78 µm, corresponding to surface area to volume ratios of 127 1/µm for rice starch and 0.49 1/µm for corn starch. Thus, a 2.5-fold difference in particle size correlated to a larger, 259-fold difference in surface area. To allow starch, a water-absorbing powder, to be used as a sole food source for Aspergillus strains, a special glass bead system was applied. AFB1 production of A. flavus Zt41 was determined to be 437.6 ± 128.4 ng/g and 90.0 ± 44.8 ng/g on rice and corn starch, respectively, while corresponding ST production levels by A. creber 2663 were 72.8 ± 10.0 µg/g and 26.8 ± 11.6 µg/g, indicating 3-fivefold higher mycotoxin levels on rice starch than on corn starch as sole carbon and energy sources. KEY POINTS: • A glass bead system ensuring the flow of air when studying powders was developed. • AFB1 and ST production of A. flavus and A. creber on rice and corn starches were studied. • 3-fivefold higher mycotoxin levels on rice starch than on corn starch were detected.

Ionic liquid-functionalized mesoporous multipod silica for simultaneously effective extraction of aflatoxin B1 and its two precursors from grain

BACKGROUND

Aflatoxin B1 (AFB1) and its precursors contaminate food and agricultural products, posing a significant risk to food safety and human health, but simultaneous and effective extraction and determination of AFB1 and its precursors with varied structures is still a challenging task.

RESULTS

In this study, a bisimidazolium-type ionic liquid functionalized mesoporous multipod silica (SiO2@mPMO-IL(im)2) was fabricated to extract AFB1 and its two precursors, i.e., averantin and sterigmatocystin. The SiO2@mPMO-IL(im)2 could simultaneously extract three targets with varied structures based on the multipods, mesopores, and multifunctional groups. The density functional theory calculations further verified the multiple interactions between SiO2@mPMO-IL(im)2 and targets. The fabricated SiO2@mPMO-IL(im)2 could effectively extract and determine three targets in grains by combing with dispersive solid-phase extraction and high-performance liquid chromatography. Good linearity (r2 > 0.9978), low LODs (0.9-1.5 μg kg-1) and LOQs (3.0-4.5 μg kg-1), satisfactory spiked recoveries (92.5%-106.8%) and high precisions (RSD<6.4%) were observed.

SIGNIFICANCE AND NOVELTY

This work demonstrates the feasibility of SiO2@mPMO-IL(im)2 for simultaneous and effective extraction of toxins with varied structures and provides a promising sample preparation for the analysis of AFB1 and its precursors in grain samples.

Variations of the fungal microbiome in Corydalis Rhizoma with different collection areas, processing methods, and storage conditions

Corydalis Rhizoma (CR, Yanhusuo in Chinese) has been widely used as an analgesic in herbal medicine and functional food. Cases of fungal and mycotoxin contamination in CR have been reported. In this study, the composition and diversity of fungal microbiome in CR samples from four herbal markets and two processing methods were investigated by DNA metabarcoding. Variations of the fungal microbiome in CR during cold and conventional storage were monitored. Results showed that Aspergillus was the dominant genus and saprotroph was the dominant trophic mode. Six potential toxigenic fungi, namely, Aspergillus fumigatus, Aspergillus ostianus, Aspergillus terreus, Penicillium citrinum, Penicillium oxalicum, and Trichothecium roseum, were detected. Differences in fungal composition and diversity among various groups based on collection areas and processing methods were also observed. Moreover, the relative abundance of dominant genera in CR samples stored at different temperatures was significantly different and changed with storage time. This study is the first to reveal the influence of collection areas, processing methods, and storage conditions on the fungal microbiome in CR, which was expected to provide a basis for control strategies of fungal contamination in the industrial chain of CR.

Effect of Aspergillus flavus contamination on the fungal community succession, mycotoxin production and storage quality of maize kernels at various temperatures

Aspergillus flavus, a notorious saprobe and opportunistic plant pathogen, alters mycotoxin contamination and biochemical components in maize kernels during processing and storage, thereby reducing the possibilities of maize end use and compromising food safety. This study explored changes in mycotoxin production, fungal community succession and biochemical components in maize kernels stored at 20, 25 and 30 °C, exposed to A. flavus. Results showed that aflatoxin B1 concentration increased over time, reaching 4.88 μg/kg at 20 °C, 167.23 μg/kg at 25 °C and 349.64 μg/kg at 30 °C after 15 days of storage, whereas the zearalenone production was characterized by an increase followed by a decrease. Correspondingly, the number of molds gradually increased and reached a stable stage after 10 days. High-throughput sequencing of the internal transcribed spacer (ITS) revealed that Eurotium dominated the fungal communities, with A. flavus reaching maximum abundance in maize kernels stored at 30 °C for 15 days. Correlation analysis indicated that the relative abundance of A. flavus was significantly negatively correlated with the content of zein and moisture (P < 0.05). Moreover, the wet milling process of maize effectively eliminated the concentration of aflatoxin B1 and zearalenone from the starch. Pasting temperature and setback value of starch decreased while peak viscosity, final viscosity and breakdown value increased with storage. These findings indicate that interactions between the epiphytic fungal community and A. flavus at elevated storage temperatures aggravate both maize quality deterioration and mycotoxin contamination. Furthermore, they have a discernible impact on the pasting properties of starch. This insight informs strategies to control fungal infections during maize processing and storage.

Impacts of Temperature and Water Activity Interactions on Growth, Aflatoxin B1 Production and Expression of Major Biosynthetic Genes of AFB1 in Aspergillus flavus Isolates

The contamination of peanuts, with Aspergillus flavus and subsequent aflatoxins (AFs) is considered to be one of the most serious, safety problems in the world. Water activity (a_w) and temperature are limiting, factors for fungal growth and aflatoxin production during storage. The objectives of this study were to integrate data on the effects of temperature (34, 37, and 42 °C) and water activity (a_w; 0.85, 0.90, and 0.95) on growth rate aflatoxin B1 (AFB1) production and up- or-downregulation of the molecular expression of biosynthetic AFB1 genes divided into three types based on their A. flavus isolate composition and AFB1 capacity in vitro: A. flavus KSU114 (high producer), A. flavus KSU114 (low producer), and A. flavus KSU121 (non-producer). The A. flavus isolates were shown to be resilient in terms of growth on yeast extract sucrose agar media when exposed to temperature and water activity as pivotal environmental factors. The optimal conditions for the fungal growth of three isolates were a temperature of 34 °C and water activity of 0.95 a_w; there was very slow fungal growth at the highest temperature of 42 °C, with different a_w values causing inhibited fungal growth. The AFB1 production for the three isolates followed the same pattern with one exception: A. flavus KSU114 failed to produce any AFB1 at 42 °C with different a_w values. All tested genes of A. flavus were significantly up- or downregulated under three levels of interaction between temperature and a_w. The late structural genes of the pathway were significantly upregulated at 34 °C under a_w 0.95, although aflR, aflS and most of the early structural genes were upregulated. Compared to 34 °C with an a_w value of 0.95, most of the expressed genes were significantly downregulated at 37 and 42 °C with a_w values of 0.85 and 0.90. Additionally, two regulatory genes were downregulated under the same conditions. The expression level of laeA was also completely associated with AFB1 production, while the expression level of brlA was linked to A. flavus colonization. This information is required to forecast the actual effects of climate change on A. flavus. The findings can be applied to improve specific food technology processes and create prevention strategies to limit the concentrations of potential carcinogenic substances in peanuts and their derivatives.

FEDformer-Based Paddy Quality Assessment Model Affected by Toxin Change in Different Storage Environments

The storage environment can significantly impact paddy quality, which is vital to human health. Changes in storage can cause growth of fungi that affects grain quality. This study analyzed grain storage monitoring data from over 20 regions and found that five factors are essential in predicting quality changes during storage. The study combined these factors with the FEDformer (Frequency Enhanced Decomposed Transformer for Long-term Series Forecasting) model and k-medoids algorithm to construct a paddy quality change prediction model and a grading evaluation model, which showed the highest accuracy and lowest error in predicting quality changes during paddy storage. The results emphasize the need for monitoring and controlling the storage environment to preserve grain quality and ensure food safety.

Impact of environmental factors on ochratoxin A: From natural occurrence to control strategy

Ochratoxin A (OTA) contamination and the associated issues of food security, food safety and economic loss are widespread throughout the world. The occurrence of OTA depends on ochratoxigenic fungi, foodstuffs and their environment. In this review, natural occurrence and control strategy of OTA, with a focus on the impact of environmental factors, are summarized. First, this manuscript introduces potentially contaminated foodstuffs, including the emerging ones which are not regulated in international legislation. Secondly, it gives an update of native producers based on foodstuffs and OTA biosynthesis. Thirdly, complicated environmental regulation is disassembled into individual factors in order to clarify their regulatory effect and mechanism. Finally, to emphasize control OTA at all stages of foodstuffs from farm to table, strategies used at crop planting, harvest, storage and processing stages are discussed.

Advanced mycotoxin control and decontamination techniques in view of an increased aflatoxin risk in Europe due to climate change

Aflatoxins are toxic secondary metabolites produced by Aspergillus spp. found in staple food and feed commodities worldwide. Aflatoxins are carcinogenic, teratogenic, and mutagenic, and pose a serious threat to the health of both humans and animals. The global economy and trade are significantly affected as well. Various models and datasets related to aflatoxins in maize have been developed and used but have not yet been linked. The prevention of crop loss due to aflatoxin contamination is complex and challenging. Hence, the set-up of advanced decontamination is crucial to cope with the challenge of climate change, growing population, unstable political scenarios, and food security problems also in European countries. After harvest, decontamination methods can be applied during transport, storage, or processing, but their application for aflatoxin reduction is still limited. Therefore, this review aims to investigate the effects of environmental factors on aflatoxin production because of climate change and to critically discuss the present-day and novel decontamination techniques to unravel gaps and limitations to propose them as a tool to tackle an increased aflatoxin risk in Europe.

Maximizing Laboratory Production of Aflatoxins and Fumonisins for Use in Experimental Animal Feeds

Warm and humid climatic conditions coupled with poor agricultural practices in sub-Saharan Africa favor the contamination of food and feed by Aspergillus flavus and Fusarium verticillioides fungi, which subsequently may produce aflatoxins (AFs) and fumonisins (FBs), respectively. The growth of fungi and the production of mycotoxins are influenced by physical (temperature, pH, water activity, light and aeration), nutritional, and biological factors. This study aimed at optimizing the conditions for the laboratory production of large quantities of AFs and FBs for use in the animal experiments. A. flavus and F. verticillioides strains, previously isolated from maize in Kenya, were used. Levels of AFB1 and total FBs (FB1, FB2, and FB3) in different growth substrates were screened using ELISA methods. Maize kernels inoculated with three different strains of A. flavus simultaneously and incubated at 29 °C for 21 days had the highest AFB1 level of 12,550 ± 3397 μg/kg of substrate. The highest level of total FBs (386,533 ± 153,302 μg/kg of substrate) was detected in cracked maize inoculated with three different strains of F. verticillioides and incubated for 21 days at temperatures of 22-25 °C in a growth chamber fitted with yellow light. These two methods are recommended for the mass production of AFB1 and FBs for animal feeding trials.

Aflatoxins in Cereals and Cereal-Based Products: Occurrence, Toxicity, Impact on Human Health, and Their Detoxification and Management Strategies

Cereals and cereal-based products are primary sources of nutrition across the world. However, contamination of these foods with aflatoxins (AFs), secondary metabolites produced by several fungal species, has raised serious concerns. AF generation in innate substrates is influenced by several parameters, including the substrate type, fungus species, moisture content, minerals, humidity, temperature, and physical injury to the kernels. Consumption of AF-contaminated cereals and cereal-based products can lead to both acute and chronic health issues related to physical and mental maturity, reproduction, and the nervous system. Therefore, the precise detection methods, detoxification, and management strategies of AFs in cereal and cereal-based products are crucial for food safety as well as consumer health. Hence, this review provides a brief overview of the occurrence, chemical characteristics, biosynthetic processes, health hazards, and detection techniques of AFs, along with a focus on detoxification and management strategies that could be implemented for food safety and security.

High speed homogenization assisted encapsulation of synergistic essential oils formulation: Characterization, in vitro release study, safety profile, and efficacy towards mitigation of aflatoxin B1 induced deterioration in rice samples

Application of essential oils to mitigate aflatoxin B₁ (AFB₁) contamination in food is a current research hotspot; however, their direct incorporation may cause toxic effects, and changes in food organoleptic properties. This work aimed to synthesize novel synergistic formulation of Pinus roxburghii, Juniperus communis, and Cupressus sempervirens essential oils by mixture design assay (PJC) and encapsulation of PJC formulation into chitosan nanocomposite (Nm-PJC) with an aim to protect stored rice (Oryza sativa L., prime staple food) against fungi and AFB₁ mediated loss of valuable minerals, macronutrients, and fatty acids. Nm-PJC was characterized through DLS, SEM, FTIR, and XRD analyses, along with controlled delivery from chitosan nanobiopolymer. Encapsulation of synergistic formulation into chitosan-nanomatrix improved antifungal (4.0 μL/mL), antiaflatoxigenic (3.5 μL/mL), and antioxidant activities (P < 0.05). Impairment in ergosterol and methylglyoxal biosynthesis along with in-silico-homology-modeling of major components with Ver-1 and Omt-A proteins advocated chemico-molecular interaction responsible for fungal growth inhibition and AFB₁ secretion. In addition, in-situ efficacy against lipid-peroxidation, fatty acid biodeterioration, and preservation of minerals, macronutrients without affecting organoleptic attributes in rice and high mammalian safety profile (9874.23 μL/kg) suggested practical application of synergistic nanoformulation as innovative smart, and green candidate to mitigate AFB₁ contamination, and shelf-life extension of stored food products.

Effect of Water Activity on Conidia Germination in Aspergillus flavus

In this study, we explored the mechanism underlying Aspergillus flavus conidia germination inhibited by decreased water activity. The impact of low water activity was analyzed at 4 h, 8 h and 12 h. Additionally, we demonstrated that low water activity affected cell shape and decreased cell sizes. Transcriptomics found numerous differentially expressed genes (DEGs) during the first 12 h of germination, with 654 DEGs observed among 4 h, 8 h and 12 h. In particular, more DEGs were detected at 8 h of germinating. Therefore, proteomics was performed at 8 h, and 209 differentially expressed proteins (DEPs) were speculated, with 94 up-regulated and 115 down-regulated. Combined analysis of KEGG of transcriptomics and proteomics demonstrated that the dominant pathways were nutrient metabolism and translation. We also found several DEGs and DEPs in the Mitogen Activated Protein Kinase (MAPK) pathway. Therefore, we concluded that low water activity inhibited conidia germination, causing unregular morphology. In addition, low water activity influenced expression of creA, TreB in carbohydrate metabolism, Clr4, RmtA in amino acid metabolism and RPL37, RPL3 in translation in Aspergillus flavus.

Natural Occurrence of Mycotoxins in Maize in North China

Mycotoxins seriously threaten the quality of maize seriously around the world. A total of 426 samples of maize kernel from northeast and northwest China were analyzed in this study. Ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) was performed to analyze the mycotoxin contamination of maize samples. The results showed that it was contaminated by mycotoxins in maize. The average contamination levels of fumonisins, deoxynivalenol, aflatoxins, zearalenone, ochratoxin A, T-2 and HT-2 were 937, 431, 22, 27, 2 and 12 μg/kg, respectively. Concentration of mycotoxins in some samples exceeded their limit, but most were still at safe levels. The contamination level of FBs and DON were most significative. The proportion of mycotoxins exceeding the maximum limit standard was in the following order: 8.0%, 8.0%, 7.0%, 1.6%, 1.4% and 0.0%. The contamination of mycotoxins in maize varies from region to region.

Predictive growth kinetic parameters and modelled probabilities of deoxynivalenol production by Fusarium graminearum on wheat during simulated storing conditions

AIMS

Mathematical models were employed to predict the growth kinetic parameters of F. graminearum and the accumulation of deoxynivalenol (DON) during wheat storage as a function of different moisture contents (MCs) and temperatures.

METHODS AND RESULTS

The colony counting method was used to quantify F. graminearum growth under different environmental conditions, and kinetic and probability models were developed to describe the effect of different MCs and temperatures on fungal growth and DON production during wheat storage. Among the employed secondary models (Arrhenius-Davey, Gibson, and Cardinal), the general polynomial best predicted the fungal growth rate under varying temperature and MC during wheat storage. According to the logistic model, DON contamination was correctly predicted in 96.5% of cases.

CONCLUSIONS

The maximum growth rate of fungi was 0.4889±0.092 Log CFU g^-1 d^-1 at 25°C and 30% moisture according to the polynomial model. At below 17°C and ≤15% moisture, no fungal growth was observed. The probability model of toxin production showed no toxin production at less than 15% moisture (a_w ≤ 0.76) and below 15°C.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first application of a probability model of DON production during wheat storage, providing a reference for preventing fungal growth and mycotoxin accumulation by F. graminearum during wheat storage and guaranteeing food product safety.

Interaction of water activity and temperature on growth, gene expression, and aflatoxin B1 production in Aspergillus flavus on Indian senna (Cassia angustifolia Vahl.)

Senna (Cassia angustifolia Vahl.) is a medicinal crop with laxative properties, and it has significant demand in the global pharmaceutical market. Senna pods are highly susceptible to aflatoxin contamination, and the successful export of pods is hindered due to the regulatory limits of importing countries. The senna pod water activity (a_w) from harvest to storage is the key factor determining AFB₁ accumulation. The temperature conditions from field to warehouse also interact with pod a_w, which influences fungal growth and AFB₁ production. The determination of an ideal combination of a_w and temperature led to the assessment of the critical control point for AFB₁ synthesis in senna. Hence, this study aimed to evaluate the influence of a_w (0.99, 0.96, 0.93, 0.90, and 0.87 a_w) and temperature (20, 28, and 37 °C) on fungal growth, gene expression (aflR and aflS), and AFB₁ production by A. flavus in senna agar medium. The fungus showed the longest lag time (7.7 days) at 20 °C with 0.87 a_w. We observed that 0.96 a_w (P < 0.01) was optimum for the diametric growth rate at 28 and 37 °C. However, the peak expression of regulatory genes (aflR and aflS) and the maximum AFB₁ production were observed only at 28 °C (0.96 a_w). The highest growth rate occurred at 37 °C, which did not favor the expression of genes and AFB₁ production. However, at 28 °C, it positively correlated with gene expression and AFB₁ production. The suppressed expression of regulatory genes and a trace amount of aflatoxin B₁ were found at 20 °C with all the tested a_w. In our experiments, the low a_w (0.87 and 0.90 a_w) suppressed the fungal growth, gene expression, and AFB₁ production of A. flavus at all of the tested temperatures (20, 28, and 37 °C). The rapid drying of senna pods with a low water activity (≤0.87 a_w) and storage at low temperature (20 °C) are ideal conditions to avoid AFB₁ and ensure the quality of produce for export.

Comparison of growth and aflatoxin B1 production profiles of Aspergillus flavus strains on conventional and isogenic GM-maize-based nutritional matrices

Maize grown in both North and South America are now predominantly genetically modified (GM) cultivars with some resistance to herbicide, pesticide, or both. There is little information on the relative colonisation and aflatoxin B₁ (AFB₁) production with maize meal-based nutritional matrices based on kernels of non-GM maize and isogenic GM-ones by strains of Aspergillus flavus. The objectives were to examine the effect of interacting conditions of temperature (25-35 °C) and water availability (0.99-0.90 water activity, a_w) on (a) mycelial growth, (b) AFB₁ production and (c) develop contour maps of optimum and marginal conditions of these parameters for four strains of A. flavus on three different non-GM and isogenic GM-maize based nutritional media. The growth of the four strains of A. flavus (three aflatoxigenic; one non-aflatoxigenic) was relatively similar in relation to the temperature × a_w conditions examined on both non-GM and GM-based matrices. Optimum growth overall was at 30-35 °C and 0.99 a_w for all four strains. Under water stress (0.90 a_w) growth was optimum at 35 °C. Statistically: non-GM, GM cultivars, temperature and a_w all significantly affected growth rates. For AFB₁ production, all single and interacting factors were statistically significant except for non-GM × GM cultivar. In conclusion, colonisation of GM- and non-GM nutritional sources was similar for the different A. flavus strains examined. The contour maps will be very useful for understanding the ecological niches for both toxigenic and non-toxigenic strains in the context of the competitive exclusion of those producing aflatoxins.

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.

The Regulatory Mechanism of Water Activities on Aflatoxins Biosynthesis and Conidia Development, and Transcription Factor AtfB Is Involved in This Regulation

Peanuts are frequently infected by Aspergillus strains and then contaminated by aflatoxins (AF), which brings out economic losses and health risks. AF production is affected by diverse environmental factors, especially water activity (a_w). In this study, A. flavus was inoculated into peanuts with different a_w (0.90, 0.95, and 0.99). Both AFB₁ yield and conidia production showed the highest level in a_w 0.90 treatment. Transcriptional level analyses indicated that AF biosynthesis genes, especially the middle- and later-stage genes, were significantly up-regulated in a_w 0.90 than a_w 0.95 and 0.99. AtfB could be the pivotal regulator response to a_w variations, and could further regulate downstream genes, especially AF biosynthesis genes. The expressions of conidia genes and relevant regulators were also more up-regulated at a_w 0.90 than a_w 0.95 and 0.99, suggesting that the relative lower a_w could increase A. flavus conidia development. Furthermore, transcription factors involved in sexual development and nitrogen metabolism were also modulated by different a_w. This research partly clarified the regulatory mechanism of a_w on AF biosynthesis and A. flavus development and it would supply some advice for AF prevention in food storage.

Molecular Aspects of Mycotoxins-A Serious Problem for Human Health

Mycotoxins are toxic fungal secondary metabolities formed by a variety of fungi (moulds) species. Hundreds of potentially toxic mycotoxins have been already identified and are considered a serious problem in agriculture, animal husbandry, and public health. A large number of food-related products and beverages are yearly contaminated by mycotoxins, resulting in economic welfare losses. Mycotoxin indoor environment contamination is a global problem especially in less technologically developed countries. There is an ongoing effort in prevention of mould growth in the field and decontamination of contaminated food and feed in order to protect human and animal health. It should be emphasized that the mycotoxins production by fungi (moulds) species is unavoidable and that they are more toxic than pesticides. Human and animals are exposed to mycotoxin via food, inhalation, or contact which can result in many building-related illnesses including kidney and neurological diseases and cancer. In this review, we described in detail the molecular aspects of main representatives of mycotoxins, which are serious problems for global health, such as aflatoxins, ochratoxin A, T-2 toxin, deoxynivalenol, patulin, and zearalenone.

Assessment of the Microbiome and Potential Aflatoxin Associated With the Medicinal Herb Platycladus orientalis

Platycladi Semen, which is derived from the dried ripe seed of Platycladus orientalis, has been used for the treatment of insomnia and constipation in China for 2000 years. However, it is susceptible to fungal and aflatoxin contamination under proper humidity and temperature during storage. Although aflatoxin contamination in Platycladi Semen has been reported preliminarily, few studies have been conducted on fungal infection and aflatoxin contamination simultaneously. Thus, this work aims to provide an in-depth understanding of fungal contamination in Platycladi Semen, and information on aflatoxin contamination. We focused on a comparison of the difference in fungal diversity between aflatoxin-contaminated and aflatoxin-free Platycladi Semen samples. First, aflatoxin levels in 11 Platycladi Semen samples, which were collected from local herbal markets in Shandong, Anhui, and Hebei provinces throughout China, were determined by IAC-HPLC-FLD, and positive confirmation of detected samples was performed by LC-MS/MS. The samples were divided into two groups, based on production or non-production of aflatoxin. We then used the Illumina MiSeq PE250 platform, and targeted the internal transcribed spacer two sequences to analyze the diversity and composition of the fungal microbiome, as well as to assess the presence of potential mycotoxin-producing fungi. Results showed that five samples were contaminated with aflatoxins, one of which exceeded the legal limits of Chinese Pharmacopeia Commission (2015). At the phylum level, the Ascomycota was the most dominant in all tested samples, with a relative abundance of 83.04-99.46%. Aspergillus (27.88-97.28%), Xerochrysium (0-28.49%), and Xeromyces (0-22.24%) were the three predominant genera. Furthermore, differences in fungal composition between the aflatoxin-contaminated and aflatoxin-free groups, as well as between different provinces were observed. A total of 74 species were identified, and four potential mycotoxin-producing fungi were detected in all samples, namely Aspergillus flavus, Aspergillus fumigatus, Fusarium poae, and Penicillium steckii. In conclusion, we report the great diversity of fungi associated with Platycladi Semen, highlight the risk to consumers of ingesting potent aflatoxin, and provide a reference for the safe application and quality improvement of Platycladi Semen.

Characteristics, Occurrence, Detection and Detoxification of Aflatoxins in Foods and Feeds

Mycotoxin contamination continues to be a food safety concern globally, with the most toxic being aflatoxins. On-farm aflatoxins, during food transit or storage, directly or indirectly result in the contamination of foods, which affects the liver, immune system and reproduction after infiltration into human beings and animals. There are numerous reports on aflatoxins focusing on achieving appropriate methods for quantification, precise detection and control in order to ensure consumer safety. In 2012, the International Agency for Research on Cancer (IARC) classified aflatoxins B1, B2, G1, G2, M1 and M2 as group 1 carcinogenic substances, which are a global human health concern. Consequently, this review article addresses aflatoxin chemical properties and biosynthetic processes; aflatoxin contamination in foods and feeds; health effects in human beings and animals due to aflatoxin exposure, as well as aflatoxin detection and detoxification methods.

Exploration of the safe water content and activity control points for medicinal and edible lotus seeds from mildew

Affected by the inner properties and the external environmental conditions, medicinal and edible lotus seeds are susceptible to mildew with fungal infection under suitable temperature and humidity conditions, leading to the production and contamination of various mycotoxins, along with threats to its quality and safety. In this study, the changes of water content (C_w) and water activity (A_w) of lotus seeds stored at 25 °C and different relative humidity conditions, as well as the correlation between them and mildew of this edible and medicinal material were studied, aiming to explore the safe C_w and A_w control points for screening out the suitable storage conditions from mildew. Blank (without fungal conidia) and experimental (artificially added with Aspergillus flavus conidia) groups of lotus seeds were stored at 25 °C and relative humidity of 40%, 50%, 60% and 70% for about 30 days, respectively. The mildew was observed and the changes of C_w, A_w, together with the production of aflatoxins were measured. Results showed that no mildew was found and aflatoxins were not detected in lotus seeds when they were stored for 30 days at 25 °C and relative humidity of 40%, 50% and 60% with C_w < 12% and A_w < 0.6. While, when the relative humidity was up to 70%, the C_w and A_w values rose quickly, and the C_w exceeded the officially-permitted level (14%). Although no mildew was observed, AFB₁ was still detected, increasing the potential risk of lotus seeds regarding aflatoxins. For warranting the quality with economic and safe storage, lotus seeds are suggested to be stored at 25 °C and relative humidity lower than 60% with 12% and 0.6 as the safe C_w and A_w control points, respectively, to prevent medicinal and edible products from mildew and the contamination of aflatoxins.

Influence of Storage Temperature and Packaging on Bacteria and Yeast Viability in a Plant-Based Fermented Food

Optimization of food storage has become a central issue for food science and biotechnology, especially in the field of functional foods. The aim of this work was to investigate the influence of different storage strategies in a fermented food product (FFP) and further determine whether the regular storage (room temperature (RT) and standard packaging (SP)) could be refined. Eight experimental conditions (four different temperatures × two packaging) were simulated and changes in FFP's microbial ecology (total bacteria, lactic acid bacteria (LAB), and yeasts) and physicochemical characteristics (pH and moisture content (MC)) were determined following 1, 3, 6, and 12 months. All conditions tested showed a decline in microbial content due to the effect of the temperature, 37 °C being the most detrimental condition, while -20 and 4 °C seemed to be better than RT in some parameters. Vacuum packaging (VP) only had a major effect on MC and we found that VP preserved greater MC values than SP at 3, 6, and 12 months. The correlation analysis revealed that total bacteria, LAB, and yeasts were positively associated, and also both pH and MC showed a correlation. According to our results and with the purpose to maintain the load of viable microorganisms, we observed that the best storage conditions should contemplate SP and freezing or cooling temperature during a period no longer than 3 months.

Recent progress of the effect of environmental factors on Aspergillus flavus growth and aflatoxins production on foods

The contamination of Aspergillus flavus and subsequent aflatoxins (AFs) has been considered as one of the most serious food safety problems due to their acute and chronic adverse effects on humans and animals. This review collects the available information from recent years on the effect of the major environmental factors such as water activity (aw), temperature, CO2, and pH on the fungal growth, the expression of AFs-related genes, and AFs production by A. flavus on foods. In particular, the relationship between the relative expression of key regulatory (aflR and aflS) and structural genes (aflD, aflO, aflQ, etc.) and AFs production under different environmental conditions are collected and discussed. The information collected in this review can be used to design control strategies of A. flavus and AFs contamination in practical applications, primarily during storage and processing. These data suggest that integrating various post-harvest methods with synergistic functions may be more efficient for the control of A. flavus growth and AFs production, although the individual environmental factors alone have an impact.

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.

Aflatoxins in Food and Feed: An Overview on Prevalence, Detection and Control Strategies

Aflatoxins produced by the Aspergillus species are highly toxic, carcinogenic, and cause severe contamination to food sources, leading to serious health consequences. Contaminations by aflatoxins have been reported in food and feed, such as groundnuts, millet, sesame seeds, maize, wheat, rice, fig, spices and cocoa due to fungal infection during pre- and post-harvest conditions. Besides these food products, commercial products like peanut butter, cooking oil and cosmetics have also been reported to be contaminated by aflatoxins. Even a low concentration of aflatoxins is hazardous for human and livestock. The identification and quantification of aflatoxins in food and feed is a major challenge to guarantee food safety. Therefore, developing feasible, sensitive and robust analytical methods is paramount for the identification and quantification of aflatoxins present in low concentrations in food and feed. There are various chromatographic and sensor-based methods used for the detection of aflatoxins. The current review provides insight into the sources of contamination, occurrence, detection techniques, and masked mycotoxin, in addition to management strategies of aflatoxins to ensure food safety and security.