Aflatoxin Control in Maize by Trametes versicolor

Aspergillus flavus is a well-known ubiquitous fungus able to contaminate both in pre- and postharvest period different feed and food commodities. During their growth, these fungi can synthesise aflatoxins, secondary metabolites highly hazardous for animal and human health. The requirement of products with low impact on the environment and on human health, able to control aflatoxin production, has increased. In this work the effect of the basidiomycete Trametes versicolor on the aflatoxin production by A. flavus both in vitro and in maize, was investigated. The goal was to propose an environmental loyal tool for a significant control of aflatoxin production, in order to obtain feedstuffs and feed with a high standard of quality and safety to enhance the wellbeing of dairy cows. The presence of T. versicolor, grown on sugar beet pulp, inhibited the production of aflatoxin B1 in maize by A. flavus. Furthermore, treatment of contaminated maize with culture filtrates of T. versicolor containing ligninolytic enzymes, showed a significant reduction of the content of aflatoxin B1.     

Characterization of Ugandan Endemic Aspergillus Species and Identification of Non-Aflatoxigenic Isolates for Potential Biocontrol of Aflatoxins

Acute stunting in children, liver cancer, and death often occur due to human exposure to aflatoxins in food. The severity of aflatoxin contamination depends on the type of Aspergillus fungus infecting the crops. In this study, Aspergillus species were isolated from households’ staple foods and were characterized for different aflatoxin chemotypes. The non-aflatoxigenic chemotypes were evaluated for their ability to reduce aflatoxin levels produced by aflatoxigenic A. flavus strains on maize grains. Aspergillus flavus (63%), A. tamarii (14%), and A. niger (23%) were the main species present. The A. flavus species included isolates that predominantly produced aflatoxins B1 and B2, with most isolates producing a high amount (>20 ug/µL) of aflatoxin B1 (AFB1), and a marginal proportion of them also producing G aflatoxins with a higher level of aflatoxin G1 (AFG1) than AFB1. Some non-aflatoxigenic A. tamarii demonstrated a strong ability to reduce the level of AFB1 by more than 95% when co-inoculated with aflatoxigenic A. flavus. Therefore, field evaluation of both non-aflatoxigenic A. flavus and A. tamarii would be an important step toward developing biocontrol agents for mitigating field contamination of crops with aflatoxins in Uganda.     

Cumulative Effects of Non-Aflatoxigenic Aspergillus flavus Volatile Organic Compounds to Abate Toxin Production by Mycotoxigenic Aspergilli

Previously, authors reported that individual volatile organic compounds (VOCs) emitted by non-aflatoxigenic Aspergillus flavus could act as a mechanism of biocontrol to significantly reduce aflatoxins and cyclopiazonic acid (CPA) produced by toxigenic strains. In this study, various combinations and volumes of three mycotoxin-reductive VOCs (2,3-dihydrofuran, 3-octanone and decane) were assessed for their cumulative impacts on four Aspergillus strains (LA1–LA4), which were then analyzed for changes in growth, as well as the production of mycotoxins, including aflatoxins, CPA and multiple indole diterpenes. Fungal growth remained minimally inhibited when exposed to various combinations of VOCs. No single combination was able to consistently, or completely, inhibit aflatoxin or CPA across all toxigenic strains tested. However, the combination of 2,3-dihydrofuran and 3-octanone offered the greatest overall reductions in aflatoxin and CPA production. Despite no elimination of their production, findings showed that combining VOCs produced solely by non-aflatoxigenic A. flavus still inhibited several agriculturally important mycotoxins, including B and G aflatoxins and CPA. Therefore, other VOC combinations are worth testing as post-harvest biocontrol treatments to ensure the prolonged effectiveness of pre-harvest biocontrol efforts.     

Aflatoxins in Maize: A Mexican Perspective

Aflatoxins are carcinogenic metabolites produced by Aspergillus flavus, a fungal pathogen that infects maize both in the field and during storage. Mexico is the center of origin of maize and its production in most parts in the country is characterized by the employment of a wide diversity of open‐pollinated genotypes adapted to certain environments. In most regions, maize is produced under rain fed conditions with low fertilizer and pesticide input and consequent low yields, probably fostering A. flavus infection in drought‐stressed plants. In addition, poor pest control increases insect damage, facilitating fungal infection and aflatoxin contamination. Ideally, management of aflatoxin contamination should begin with the employment of resistant genotypes as has been demonstrated by several U.S. breeding programs. However, in Mexico the wide genetic diversity of maize has not been fully exploited to identify resistance to aflatoxin contamination in breeding programs, thus impeding the reduction of aflatoxin levels in the field. Additional complications come from the fact that transgenic maize expressing insecticidal protein or any other trait to reduce aflatoxin is not viable in Mexico due to a government prohibition on the use of genetically modified maize. Maize is a staple crop in Mexico with high consumption in forms such as tortillas; thus, aflatoxin contamination is a significant threat to human health. Although aflatoxins are partially destroyed during the alkaline cooking procedure (called nixtamalization) to prepare tortillas, residual levels of aflatoxins might be considerable. Although important research has been conducted in several aspects of aflatoxin contamination of maize by universities, agricultural centers, and some government agencies, a full mycotoxin research program is needed in Mexico to ascertain the extents of aflatoxin contamination in different parts of the country and to develop economically viable technology to reduce aflatoxin exposure.     

Comparison of Expression of Secondary Metabolite Biosynthesis Cluster Genes in Aspergillus flavus,A. parasiticus,and A. oryzae

Fifty six secondary metabolite biosynthesis gene clusters are predicted to be in the Aspergillus flavus genome. In spite of this, the biosyntheses of only seven metabolites, including the aflatoxins, kojic acid, cyclopiazonic acid and aflatrem, have been assigned to a particular gene cluster. We used RNA-seq to compare expression of secondary metabolite genes in gene clusters for the closely related fungi A. parasiticus, A. oryzae, and A. flavus S and L sclerotial morphotypes. The data help to refine the identification of probable functional gene clusters within these species. Our results suggest that A. flavus, a prevalent contaminant of maize, cottonseed, peanuts and tree nuts, is capable of producing metabolites which, besides aflatoxin, could be an underappreciated contributor to its toxicity.     

Toxigenic Potential of Aspergillus Species Occurring on Maize Kernels from Two Agro-Ecological Zones in Kenya

Two agro-ecological zones in Kenya were selected to compare the distribution in maize of Aspergillus spp. and their toxigenicity. These were Nandi County, which is the main maize growing region in the country but where no human aflatoxicoses have been reported, and Makueni County where most of the aflatoxicosis cases have occurred. Two hundred and fifty-five households were sampled in Nandi and 258 in Makueni, and Aspergillus was isolated from maize. Aspergillus flavus and A. parasiticus isolates were tested for the presence of aflD and aflQ genes. Positive strains were induced to produce aflatoxins on yeast extract sucrose and quantified using liquid chromatography-tandem mass spectrometry (LCMSMS). Aspergillus flavus was the most common contaminant, and the incidence of occurrence in Nandi and Makueni was not significantly different (82.33% and 73.26%, respectively). Toxigenic strains were more prevalent than non-toxigenic strains. All the toxigenic strains from Makueni were of the S-type while those from Nandi belonged to the L-type. Quantitative differences in aflatoxin production in vitro between isolates and between strains were detected with S strains producing relatively larger amounts of total aflatoxins, B toxins and lower values for G toxins. This was in accord with the frequent aflatoxicosis outbreaks in Makueni. However some L strains produced considerable amounts of B toxins. Given the widespread distribution of toxigenic strains in both regions, the risk of aflatoxin poisoning is high when favorable conditions for toxin production occur.     

Detoxification of Aflatoxin-Contaminated Maize by Neutral Electrolyzed Oxidizing Water

Aflatoxins, a group of extremely toxic mycotoxins produced by Aspergillus flavus, A. parasiticus and A. nomius, can occur as natural contaminants of certain agricultural commodities, particularly maize. These toxins have been shown to be hepatotoxic, carcinogenic, mutagenic and cause severe human and animal diseases. The effectiveness of neutral electrolyzed oxidizing water (NEW) on aflatoxin detoxification was investigated in HepG2 cells using several validation methodologies such as the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, the induction of lipid peroxidation, the oxidative damage by means of glutathione modulation, the Ames test and the alkaline Comet assay. Our results showed that, after the aflatoxin-contaminated maize containing 360 ng/g was soaked in NEW (60 mg/L available chlorine, pH 7.01) during 15 min at room temperature, the aflatoxin content did not decrease as confirmed by the immunoaffinity column and ultra performance liquid chromatography methods. Aflatoxin fluorescence strength of detoxified samples was similar to untreated samples. However, aflatoxin-associated cytotoxicity and genotoxicity effects were markedly reduced upon treatment. According to these results, NEW can be effectively used to detoxify aflatoxin-contaminated maize.     

Influence of Temperature and Humidity on Biodeterioration and Aflatoxin Production in Groundnut Fodder by Aspergillus Flavus

Abstract

The Influence of temperature and relative humidity (RH) on biodeterioration of groundnut fodder and aflatoxin elaboration by Aspergillus flavus was investigated. Though aflatoxin production was observed at all incubation temperature tried, its production was maximum at 25°C. The amount of aflatoxin production decreased significantly with increase in incubation temperature. When a marginal increase in total proteins and ash content was recorded, cellulose, lignin, starch and total nitrogen content decreased significantly due to A. flavus infestation. This was maximum at 25°C and decreased both with an increase or decrease of incubation temperature. Groundnut fodder supported significant weight loss due to A. flavus infestation and it was maximum at 25°C. RH of 90 and above was more conducive for aflatoxin elaboration. A. flavus could elaborate aflatoxins even at RH 30 which, however, was only in trace amounts.     

Safety and efficacy evaluation of aqueous citric acid to degrade B-aflatoxins in maize.

Chemical inactivation of aflatoxin B1 (AFB1) and aflatoxin B2 (AFB2) in maize grain by means of 1N aqueous citric acid was confirmed by the AFLATEST immunoaffinity column method, high performance liquid chromatography (HPLC), and the Ames test (Salmonella-microsomal screening system). The AFLATEST assay showed that aflatoxins in the maize grain with an initial concentration of 29 ng/g were completely degraded and 96.7% degradation occurred in maize contaminated with 93 ng/g when treated with the aqueous citric acid. Aflatoxin fluorescence strength of acidified samples was much weaker than untreated samples as observed in HPLC chromatograms. On the other hand, the Ames test results indicated that the mutagenic activity of acidified samples was greatly reduced compared with that of untreated samples based on his- --> his+ reversions in the Salmonella TA100 strain. Chemical inactivation appears to be a promising method of removing aflatoxin from food commodities.     

Aspergillus flavus and Total Aflatoxins Occurrence in Dairy Feed and Aflatoxin M1 in Bovine Milk in Aguascalientes,Mexico

Contamination of food chains by toxigenic fungi and aflatoxins is a global problem that causes damage to human health, as well as to crop and livestock production. The objective is to evaluate Aspergillus flavus and total aflatoxins (AFs) occurrence in totally mixed rations (TMRs) for dairy cows and aflatoxin M₁ (AFM₁) in milk for human consumption. Ninety-nine dairy production units located in Aguascalientes, Mexico, were randomly selected, and samples were collected from TMRs, raw milk, and milk marketed in the city in two consecutive agricultural cycles. AFs were quantified in TMRs and milk by indirect enzyme immunoassay and HPLC; aflatoxigenic and molecular (PCR) capacity of monosporic A. flavus isolates in the feed was characterized. All feed, raw, and pasteurized milk samples showed aflatoxin contamination (26.0 ± 0.4 µg/kg, 32.0 ± 1.0, and 31.3 ± 0.7 ng/L, respectively), and a significant proportion (90.4, 11.3, and 10.3%) exceeded the locally applied maximum permissible limits for feed and milk (20.0 µg/kg and 50 ng/L). Aflatoxin contamination in both TMRs and milk indicated a seasonal influence, with a higher concentration in the autumn–winter cycle when conditions of higher humidity prevail. The results obtained suggest the existence of contamination by aflatoxigenic A. flavus and aflatoxins in the diet formulated for feeding dairy cows and, consequently, in the dairy food chain of this region of the Mexican Highland Plateau.     

Aflatoxin Contamination,Its Impact and Management Strategies: An Updated Review

Aflatoxin, a type of mycotoxin, is mostly produced by Aspergillus flavus and Aspergillus parasiticus. It is responsible for the loss of billions of dollars to the world economy, by contaminating different crops such as cotton, groundnut, maize, and chilies, and causing immense effects on the health of humans and animals. More than eighteen different types of aflatoxins have been reported to date, and among them, aflatoxins B1, B2, G1, and G2 are the most prevalent and lethal. Early detection of fungal infection plays a key role in the control of aflatoxin contamination. Therefore, different methods, including culture, chromatographic techniques, and molecular assays, are used to determine aflatoxin contamination in crops and food products. Many countries have set a maximum limit of aflatoxin contamination (2–20 ppb) in their food and agriculture commodities for human or animal consumption, and the use of different methods to combat this menace is essential. Fungal infection mostly takes place during the pre- and post-harvest stage of crops, and most of the methods to control aflatoxin are employed for the latter phase. Studies have shown that if correct measures are adopted during the crop development phase, aflatoxin contamination can be reduced by a significant level. Currently, the use of bio-pesticides is the intervention employed in many countries, whereby atoxigenic strains competitively reduce the burden of toxigenic strains in the field, thereby helping to mitigate this problem. This updated review on aflatoxins sheds light on the sources of contamination, and the on occurrence, impact, detection techniques, and management strategies, with a special emphasis on bio-pesticides to control aflatoxins.     

Effect of Lactic Acid Bacteria on the Fermentation Quality and Mycotoxins Concentrations of Corn Silage Infested with Mycotoxigenic Fungi

This study was conducted to evaluate the effect of lactic acid bacteria (LAB) on fermentation quality, mycotoxin concentrations, and microbial communities of whole-crop corn silages infested with mycotoxigenic fungi. Cultured spores (10⁶ cfu/mL) of mycotoxigenic Aspergillus flavus and Fusarium graminearum were sprayed (5 mL) on corn forage on 27 July and 10 August 2018. On 21 August 2018, sprayed (FI; 3 plots) and unsprayed (NFI; 3 plots) corn forage were harvested at the 1/2 kernel milk line stage, followed by chopping and ensiling without inoculants (CON), or with Lactobacillus buchneri (LB, 1 × 10⁶ cfu/g FW), Lactobacillus plantarum (LT, 1 × 10⁶ cfu/g FW), or L. buchneri + L. plantarum (BT: both L. buchneri and L. plantarum applied at 0.5 × 10⁶ cfu/g FW). After 90 d of ensiling, FI silages had a higher (p < 0.05) pH value and higher acetic acid (ACA), ethanol, and ammonia nitrogen (ammonia N) concentrations, but lower (p < 0.05) lactic acid (LA) concentrations than NFI silage. The inoculants decreased pH and increased LA concentration and LA/ACA compared with CON. The aflatoxin B₁ (AFB₁) was only detected in FI fresh corn and silages; ensiling decreased (p < 0.05) AFB₁ concentration compared with fresh corn, and LB and BT decreased AFB₁ concentration compared with CON. The zearalenone (ZEN), deoxynivalenol (DON), and fumonisin B₁ (FB₁) concentrations were similar (p < 0.05) for NFI silages, while ZEN concentration in BT was the lowest (p < 0.05) among all FI silages; DON and FB₁ concentrations in LB, LT, and BT silages were significantly lower (p < 0.05) than those of CON in FI silages. The fungal infestation increased the bacterial and fungal diversity of silages compared with NFI silages. The FI silages had a higher relative abundance (RA) of Lactobacillus, Weissella, Wickerhamomyces, Pichia, and Epicoccum than the corresponding NFI silages. The RA of Aspergillus and Fusarium markedly decreased after 90 d of ensiling, and the inoculation expanded this trend irrespective of fungal infestation. The Penicillium in FI silages survived after 90 d of ensiling, while the inoculants decreased the RA of Penicillium. Inoculants mitigate the adverse effects of fungal infestation on corn silage quality by changing the bacterial and fungal communities.     

Current Research on Reducing Pre‐ and Post‐harvest Aflatoxin Contamination of U.S. Almond,Pistachio, and Walnut

Aflatoxins are considered to be potent carcinogens and teratogens to humans and farm animals. A variety of species of the fungal genus Aspergillus (mainly A. flavus and A. parasiticus) synthesize aflatoxins. Spores of these fungi are common in air and soil of agricultural areas of temperate and tropical environments. Because aflatoxigenic fungi are ubiquitous and opportunistic, aflatoxin contamination has become a food safety concern. The chief U.S. crops affected by the threat of contamination with aflatoxin include corn, peanuts, cottonseed, and certain tree nuts. Additionally, aflatoxin contamination has also become an international trade issue. Major trading partners of U.S. agricultural products have set total aflatoxin action threshold levels at four ng/g (ppb). This action level is far below the 20 ppb level recommended by the U.S. Food and Drug administration for domestic foods. Almonds, pistachios and walnuts are one of the major food commodities affected by food safety and trade issues associated with aflatoxin contamination. Commercial domestic production of these tree nuts in the U.S. is entirely in California. Moreover, 50 to 75% of domestically produced tree nuts are exported, chiefly to countries of the European Union (EU), which adhere to the four ppb action threshold level. Scientists at the USDA's Western Regional Research Center and the University of California, Davis' Department of Pomology and Kearney Agricultural Center have developed products and methods to reduce aflatoxin contamination of tree nuts. Control of insect pests in tree nut orchards is a major strategy to curtail aflatoxin contamination. Insect feeding damage can lead to fungal infection and concomitant aflatoxin contamination. This is especially the case with navel orangeworm on pistachio and almond. A new and potent lure has been developed to control codling moth, a major insect pest of walnuts whose feeding damage potentially leads to fungal infection. Through breeding and genetic engineering, new varieties of almonds and walnuts have been developed which are resistant to insect attack. New orchard management strategies have been prescribed to reduce reservoirs of A. flavus in tree nut orchards. A number of saprophytic yeasts, natural to tree nut orchards, have been discovered which show promise as biological control agents of A. flavus, in vitro, and are awaiting field testing. New and improved risk assessment models have been developed for sampling and measuring aflatoxin contamination through the processing stream and in bulk shipping lots of tree nuts. An automated sorter that detects and removes aflatoxin contaminated nuts from a processing stream in real time was developed. It was also concluded that methods currently used for hand‐cracking of closed shell pistachios result in a higher risk of aflatoxin contamination. Perhaps the foremost breakthrough to date, however, is that constituents of walnut seed coat, especially from the cultivar ‘Tulare’, are potent inhibitors of aflatoxin biosynthesis, capable of rendering aflatoxigenic A. flavus virtually atoxigenic.     

A Survey Using Normal Phase Hplc of Aflatoxins in Domestic and Imported Foods and Dairy Products in the Ussr

Abstract

An improved normal phase HPLC method has been developed to study the occurrence of aflatoxins B₁, B₂, G₁, G₂ and M₁ in domestic and imported foods. Ether-methanol-water (95:5:1) mobile phase and fluorometric detector with silica gel packed flow cell were used. The detection limit of the method was 0.1 ug/kg for aflatoxin B₁, coefficients of variation were 11% and 8.5% at contamination levels 10 and 100 ug/kg of aflatoxin B₁ respectively. Recoveries of added aflatoxins B₁, B₂, G₁, G₂ for corn ranged from 78% to 88%. This method allows the determination of aflatoxins B₁, B₂, G₁, G₂, and M₁, B_2a, M_2a as well as other aflatoxin metabolites. The method is used in monitoring aflatoxin contamination of foods, the first stage of which is a preliminary screening of samples by TLC method (the detection limit is 1.0 ug/kg for aflatoxin B₁). A survey of the occurrence of aflatoxins B₁, B₂, G₁, G₂, in Soviet domestic and imported cereals, nuts, beans, and oil seeds harvested in 1985-87 (over 4300 samples) as well as aflatoxin M₁ in domestic dairy products (over 250 samples) was carried out using HPLC and TLC methods. It was shown that 26.9% of imported peanuts, 2.2% of corn and 6.2% of barley were contaminated by aflatoxins at levels exceeding the maximum tolerated level established in the USSR (5 ug/kg for aflatoxin B₁ in foods of all kinds excluding baby foods). Maximum concentrations were 3600, 155 and 8.0 ug/kg respectively. As much as 28.3% of domestic cotton seed samples, which were chosen for the analysis due to toxic effects on animals, were also contaminated by aflatoxins. The USSR aflatoxin monitoring system was demonstrated to be effective during this study.     

aflN Is Involved in the Biosynthesis of Aflatoxin and Conidiation in Aspergillus flavus

Aspergillus flavus poses a threat to society economy and public health due to aflatoxin production. aflN is a gene located in the aflatoxin gene cluster, but the function of AflN is undefined in Aspergillus flavus. In this study, aflN is knocked out and overexpressed to study the function of AflN. The results indicated that the loss of AflN leads to the defect of aflatoxin biosynthesis. AflN is also found to play a role in conidiation but not hyphal growth and sclerotia development. Moreover, AlfN is related to the response to environmental oxidative stress and intracellular levels of reactive oxygen species. At last, AflN is involved in the pathogenicity of Aspergillus flavus to host. These results suggested that AflN played important roles in aflatoxin biosynthesis, conidiation and reactive oxygen species generation in Aspergillus flavus, which will be helpful for the understanding of aflN function, and will be beneficial to the prevention and control of Aspergillus flavus and aflatoxins contamination.     

Overview on aflatoxins and oxidative stress

Aflatoxins are naturally occurring mycotoxins that are produced by many species of Aspergillus, a fungus, mainly by Aspergillus flavus and Aspergillus parasiticus. Aflatoxins, especially aflatoxin B1 (AFB1), are very potent carcinogens in many species, including humans, birds, swine, fish, and rodents. The oxidative stress caused by AFB1 may be one of the underlining mechanisms for AFB1-induced cell injury and DNA, protein and lipid damages, which lead to tumorigenesis. This review presents an overview on aflatoxins and oxidative stress, with an emphasis on the protective role of the antioxidants.     

Mould incidence and mycotoxin contamination in maize kernels from Swat Valley,North West Frontier Province of Pakistan

Mould incidence and aflatoxin B1 (AFB1) and ochratoxin A (OTA) contamination as well as proximate composition and minerals content of maize kernels from Swat Valley, North West Frontier Province of Pakistan was studied during the year, 2007. Results indicated that the mean moisture content of the kernels was within the recommended safe storage levels of ?15%. Across the whole valley, Aspergillus, Fusarium, Penicillium and Rhizopus were the most predominant fungal genera identified and amongst the mycotoxigenic species, Aspergillus flavus had the highest incidence. AFB1 content ranged from none to 30.92 μg/kg with the average values of 14.94 and 16.22 μg/kg for Upper and Lower Swat regions, respectively. Similar trend was observed for OTA with the contamination level ranged from <0.001 to 7.32 μg/kg. A significant numbers of samples contained AFB1 and OTA levels above the safe limits as recommended by the USFDA and EU but on the average the results were within the safe limit. These results indicate that maize consumers in Swat Valley may be exposed to the danger of aflatoxins and ochratoxins poisoning. Thus, there is a need for policy makers to establish and enforce maize quality standards and regulations related to moulds and mycotoxins across the area.     

The International Mycotoxin Check Sample Programme

Abstract

Each year, laboratories in more than 40 countries around the world involved in the analysis of aflatoxins of food, control the quality of their analytical results by participating in the International Mycotoxin Check Sample Programme. Identical portions of homogenized samples of peanuts or maize, contaminated with aflatoxins B₁, B₂, G₁ and G₂, and of lyophilized milk, contaminated with aflatoxin M₁, are distributed to over 300 laboratories. In 1988, a sample of ochratoxin A contaminated wheat flour was also distributed to about 150 interested laboratories. By analysing these samples, the participating analyst can compare his own results, obtained using the method of his choice, with those of a large number of other laboratories and can take steps to modify and improve techniques if his results do not compare favourably. Participation in the programme is without charge and samples are distributed about once each year. Interested laboratories are encouraged to participate in future surveys.     

Cultural Methods for Aflatoxin Detection

Aflatoxins present important food safely problems in both developed and developing countries. Contamination is monitored in developed countries using enzyme‐linked immunusorbent assay (ELISA)‐ and high‐performance liquid chromatography (HPLC)‐based assays, both of which may be too expensive for routine use in many developing countries. There is a need for inexpensive alternative approaches to detect aflatoxins in lots of foods and feeds. Reviewed here are culture‐based methods that determine if a sample is contaminated with aflatoxigenic fungi. These approaches include 1) blue fluorescence of aflatoxin B₁, particularly when enhanced by including β‐cyclodextrin in the culture medium, 2) yellow pigment production, and 3) color change on exposure to ammonium hydroxide vapor. The presence of aflatoxin B₁ can be detected by its blue fluorescence, which is enhanced when the toxin complexes with the hydrophobic pocket of β‐cyclodextrin. The yellow pigment and ammonium hydroxide vapor tests are based on the production of yellow anthraquinone biosynthetic intermediates in the aflatoxin pathway. These compounds act as pH indicator dyes, which are more visible when they have turned red at alkaline pH. Because these tests are based on two different mechanisms, it has been possible to combine them into a single test. In a study of 517 A. flavus isolates from the Mississippi Delta, the combined assay reduced false positives for aflatoxigenicity to 0%, and false negatives to 7%. The increased predictive power of the combined cultural assay may enable its use for inexpensively identifying potential aflatoxin contamination in feeds and foods.     

Aflatoxin-producing fungi associated with Nigerian maize

Maize samples were obtained from different locations—namely Aba, Abakaliki, Afikpo, Okigwe, and Owerri—all in southeast Nigeria. Twelve mold species of the genera Aspergillus, Penicillium, Cladosporium, Alternaria, Fusarium, and Acremonium (Cephalosporium) were isolated. The presence of aflatoxin B₁ was detected in 80% of the samples by the characteristic blue fluorescence that appeared on silica gel coated thin layer chromatography plates when viewed with a long-wave ultraviolet radiation source alongside an aflatoxin standard. Eight isolates of the Aspergillus flavus group obtained from the maize samples were tested for aflatoxin production. Natural medium (maize) at 26°C and moisture content adjusted to no less than 20% was used. Aflatoxin was produced to some degree by 87.5% of the isolates. There was no aflatoxin production at a market moisture content of 5.4% and temperature of 25, 30, and 35°C. However, at 26°C and increased moisture contents of 22.3–24.9%, varying amounts of aflatoxin were produced. © 1994 by John Wiley & Sons, Inc..