Isolation of methyl syringate as a specific aflatoxin production inhibitor from the essential oil of Betula alba and aflatoxin production inhibitory activities of its related compounds

Methyl syringate was isolated from the essential oil of Betula alba as an aflatoxin production inhibitor. It inhibited aflatoxin production of Aspergillus parasiticus and Aspergillus flavus with IC₅₀ values of 0.9 and 0.8 mM, respectively, without significantly inhibiting fungal growth. Methyl syringate reduced mRNA levels of genes (aflR, pksA, and omtA) encoding proteins required for aflatoxin biosynthesis. Methyl gallate, methyl 3,4,5-trimethoxybenzoate, and methyl 3-O-methylgallate inhibited both aflatoxin production and fungal growth of A. parasiticus and A. flavus. However, their acids and syringic acid did not inhibit aflatoxin production and growth of A. parasiticus significantly, although gallic acid inhibited aflatoxin production of A. flavus with selectivity. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of methyl syringate was much weaker than that of gallic acid. These results showed that methyl syringate has a unique inhibitory activity toward aflatoxin production with a different mode of action from that of gallic acid.     

Phenolic compounds in peanut seeds: Enhanced elicitation by chitosan and effects on growth and aflatoxin B1 production by Aspergillus flavus

Effects of chitosan and Aspergillus flavus to enhance elicitation of phenolic compounds in viable peanut seeds were conducted at two water activity levels. In vitro effects of phenolic acids on A. flavus growth and aflatoxin B₁ production were also studied. Chitosan enhanced elicitation of free phenolic compounds (FPC) at Aw .85 and .95 levels. A. flavus initially decreased and subsequently increased FPC content, but bound phenolic compounds (BPC) decreased during incubation. Chitosan + A. flavus treatment caused an increase in FPC reaching a plateau between 24–48 h at Aw .85 while BPC levels increased over the same period at both Aw levels. Major free and bound phenolic acids detected were p‐coumaric, ferulic and an unknown phenolic acid eluting at a retention time of 22 min. Generally, chitosan significantly enhanced elicitation of free ferulic and p‐coumaric acids and bound p‐coumaric acid at Aw .95. Free unknown phenolic and bound ferulic acids at Aw .85 were enhanced by chitosan. A. flavus caused significant induction of bound p‐coumaric and ferulic acids and free unknown phenol at Aw .85. Chitosan + A. flavus enhanced free p‐coumaric (3 h) and unknown phenolic acids and bound p‐coumaric acid at Aw .95 while bound ferulic acid was enhanced at Aw .85. Chitosan limited A. flavus growth and subsequent aflatoxin production by inducing susceptible tissues to produce more preformed phenolic compounds.

Analysis of liquid cultures of A. flavus revealed that p‐coumaric, ferulic, and vanillic acids and a mixture of these phenolic acids slightly inhibited mycelial growth. Production of aflatoxin B₁ by A. flavus was completely inhibited at 1 mM and 10 mM concentrations of the phenolic acids and their mixture on four days of incubation. Mode of action of phenolic acids is likely on the secondary pathway for aflatoxin B₁ production and not on the primary metabolism for fungal growth.     

Phenolic compounds in peanut seeds: Enhanced elicitation by chitosan and effects on growth and aflatoxin b1 production by aspergillus flavus

Effects of chitosan and Aspergillus flavus to enhance elicitation of phenolic compounds in viable peanut seeds were conducted at two water activity levels. In vitro effects of phenolic acids on A. flavus growth and aflatoxin B₁ production were also studied. Chitosan enhanced elicitation of free phenolic compounds (FPC) at Aw .85 and .95 levels. A. flavus treatment initially decreased and subsequently increased FPC content, but bound phenolic compounds (BPC) decreased during incubation. Chitosan + A. flavus treatments caused an increase in FPC that reached a plateau between 24–48 h at Aw .85 while BPC levels increased over the same time period at both Aw levels. The major free and bound phenolic acids detected were p‐coumaric and ferulic acids and an unknown phenol that eluted at a retention time of 22 min. Generally, chitosan treatment significantly enhanced elicitation of free ferulic and p‐coumaric acids and bound p‐coumaric acid at Aw .95. Free unknown phenolic and bound ferulic acids at Aw .85 were enhanced by chitosan. A. flavus treatment caused significant induction of bound p‐coumaric and ferulic acids and free unknown phenol at Aw .85. Chitosan + A. flavus treatment measure to reduce or eliminate pre‐harvest contamination by A. flavus and aflatoxins contributes to sustainable agriculture, especially to developing countries.

The enhanced elicitation of preformed phenolic compounds by chitosan may provide seed tissues an additive or synergistic effect in controlling aflatoxin‐producing fungi and preventing aflatoxin contamination. Further, such investigation will help elucidate the biochemical basis of elicitor‐host interaction that contribute to defensive responses of host tissues. Identification of biochemical factors in induced resistance involves a refinement in the separation and identification of induced phenolic compounds. Methodologies such as spectrophotometric assay or reverse‐phase high performance liquid chromatography (HPLC) may be used to evaluate phenolic compound induction by these elicitors. In addition, these compounds can be tested on their effects on A. flavus mycelial growth and subsequent aflatoxin production in vitro.

Hence, a study on the possible role of phenols on the natural resistance of peanuts to A. flavus invasion was conducted with the following objectives: 1) to quantitate changes in free and bound phenolic compounds influenced by chitosan, A. flavus, and water activity (Aw) levels by Folin‐Ciocalteu assay; 2) to separate, identify, and quantitate free and bound phenolic acids influenced by elicitors and Aw levels; and 3) to determine the effects of phenolic acids in liquid cultures at different concentrations on mycelial growth and aflatoxin B₁ production by A. flavus.     

Modelling the Probability of Growth and Aflatoxin B1 Production of Aspergillus Flavus under Changing Temperature Conditions in Pistachio Nuts

The aim of this work was to use probability models for the prediction of growth and aflatoxin production by Aspergillus flavus as a strategy to mitigate the aflatoxin presence in pistachio nuts during postharvest. Logistic models, with temperature and time as explanatory variables, were fitted to the probability of growth and aflatoxin B₁ (AFB1) production under constant temperature levels, afterwards they were used to predict probabilities under non-isothermal scenarios. The models obtained showed levels of concordance from 80 to 100% in most of the cases. Moreover, the presence of AFB1 in pistachio nuts could be correctly predicted through AFB1 models developed in agar medium or through growth models in pistachio nuts. These findings can support decision making, at transport and storage level, and could be used by producers and processors to predict the time for AFB1 production by A. flavus in pistachio nuts in postharvest.     

The application of novel rotary plasma jets to inhibit the aflatoxin-producing Aspergillus flavus and the spoilage fungus,Aspergillus niger on peanuts

The major safety risk of peanuts is contamination with aflatoxin. Cold atmospheric plasma (CAP) has been demonstrated to inactivate fungi effectively. In this study, a novel CAP device with a rotary jet system was used to inactivate the existing A. flavus and A. niger on peanuts. The initial inoculation levels were 6.39 and 5.83 log CFU/g of A. flavus and A. niger, respectively. After treatments at 180 W for 7.5 min and 200 W for 5 min, A. flavus was not detected. For A. niger, the treatments at 180 W for 10 min and 200 W for 5 min resulted in undetected population. Observation under scanning electron microscope revealed the fungal spores were evidently damaged. The growth of A. flavus and aflatoxin concentrations were significantly lower (p < 0.05) on the group treated with 200 W for 5 min than other treatment groups stored for 29 d. Oil quality indexes of the CAP-treated peanuts were maintained in the range of excellent grades. This study demonstrated CAP effectively inhibited fungal growth and toxin production without adversely affected oil quality.     

The growth and aflatoxin production of Aspergillus flavus strains on a cheese model system are influenced by physicochemical factors

Traditional cheeses may be contaminated by aflatoxin-producing Aspergillus flavus during the ripening process, which has not been sufficiently taken into account. The objectives of this study were to evaluate the influence of water activity (a_w), pH, and temperature on the lag phases, growth, and aflatoxin production of 3 A. flavus strains (CQ7, CQ8, and CG103) on a cheese-based medium. The results showed that the behavior of A. flavus strains was influenced by pH, a_w, and temperature conditions. The CQ7 strain showed the maximum growth at pH 5.5, 0.99 a_w, and 25°C, whereas for CQ8 and CQ103 strains, no differences were obtained at pH 5.5 and 6.0. In general, low pH, a_w, and temperature values increased the latency times and decreased the growth rate and colony diameter, although a_w and temperature were the most limiting factors. Maximum aflatoxin production on the cheese-based medium occurred at pH 5.0, 0.95 a_w, and 25 or 30°C, depending on the strain. This study shows the effect of pH, a_w, and temperature factors on growth and aflatoxin production of 3 aflatoxigenic A. flavus strains on a cheese-based medium. The findings may help to design control strategies during the cheesemaking process and storage, to prevent and avoid aflatoxin contamination by aflatoxigenic molds.     

Effect of γ‐irradiation on aflatoxin B1 production by Aspergillus flavus and chemical composition of three crop seeds

The effect of γ‐irradiation on aflatoxin B₁ production by Aspergillus flavus, and the chemical composition of some different crop seeds were investigated. A. flavus infected seeds behaved differently according to their principal constituents. A. flavus caused an increase in protein and decrease in lipids and carbohydrate contents of wheat, soyabean and fababean seeds. Growth of A. flavus and production of aflatoxin B₁ was inhibited at a dose level of 5 kGy. A. flavus utilizes carbohydrates of seeds for its growth and aflatoxin production. Crops were arranged, in descending order, according to aflatoxin produced in seeds as wheat > soyabean > fababean. There were no changes in chemical constituents of irradiated seeds, such as protein, lipids, and carbohydrates.     

Complex regulation of the aflatoxin biosynthesis gene cluster of Aspergillus flavus in relation to various combinations of water activity and temperature

A microarray analysis was performed to study the effect of varying combinations of water activity and temperature on the activation of aflatoxin biosynthesis genes in Aspergillus flavus grown on YES medium. Generally A. flavus showed expression of the aflatoxin biosynthetic genes at all parameter combinations tested. Certain combinations of a_w and temperature, especially combinations which imposed stress on the fungus resulted in a significant reduction of the growth rate. At these conditions induction of the whole aflatoxin biosynthesis gene cluster occurred, however the produced aflatoxin B₁ was low. At all other combinations (25 °C/0.95 and 0.99; 30 °C/0.95 and 0.99; 35 °C/0.95 and 0.99) a reduced basal level of cluster gene expression occurred. At these combinations a high growth rate was obtained as well as high aflatoxin production. When single genes were compared, two groups with different expression profiles in relation to water activity/temperature combinations occurred. These two groups were co-ordinately localized within the aflatoxin gene cluster. The ratio of aflR/aflJ expression was correlated with increased aflatoxin biosynthesis.     

Aspergillus flavus population isolated from soil of Argentina's peanut‐growing region. Sclerotia production and toxigenic profile

The Aspergillus flavus population was evaluated in the period 1998–2001 in soil samples from the peanut‐growing region in Argentina. A total of 369 A flavus isolates were examined for sclerotia, aflatoxin and cyclopiazonic acid production. The L phenotype was isolated in a higher percentage than the S phenotype and represented 59% of the total isolates. Statistical analysis showed significant differences between L, S and non‐sclerotial strains with regard to aflatoxin and cyclopiazonic acid production (p < 0.05). The S strains produced higher mycotoxin levels than the L and non‐sclerotial strains. About 10% of the S strains had an unusual pattern of mycotoxin production because they simultaneously produce aflatoxins B and G and CPA. The S_BG strains isolated in the present study have all morphological and microscopic characteristics of A flavus. These strains are of concern in food safety, as there is a higher probability of aflatoxin contamination in peanuts. Copyright © 2005 Society of Chemical Industry     

Preliminary studies of the effects of heat and gamma irradiation on the production of aflatoxin B1 in static liquid culture,by Aspergillus flavus link NRRL 5906

Aflatoxin B₁ production by a strain of Aspergillus flavus NRRL 5906 was examined in static liquid culture in maize meal broth (MMB) and maize meal broth supplemented with 2% glucose and 2% peptone (AMMB). Erlenmeyer flasks were inoculated with 1.0 ml aliquots of fungal spores which had been heat-treated (60°C for 30 min) under low humidity (< 45% R.H. dry heat) or high humidity conditions (>85% R.H., moist heat) followed by gamma irradiation with either 0.0, 3.5 or 4.0 kGy. AMMB supported 6–17 times more vegetative growth (depending on the heat and dose combination) than spores incubated in MMB alone. High inoculum size of control unheated spores (log CFU/g, 6.9) yielded the least aflatoxin B₁ in flasks containing AMMB (8.2–19.3 μg/ml). A dose of 3.5 kGy reduced by 3.2–3.8 log cycles the viable inoculum of control unheated spores, resulting in 2–5 fold increase in aflatoxin B₁ formed in flasks containing AMMB. Increasing the applied load to 4.0 kGy, however, reduced aflatoxin B₁ levels formed in AMMB to similar or lower levels than found in flasks inoculated with control unirradiated spores. Combination treatment of A. flavus with dry heat and 3.5 kGy reduced the spore inoculum size by about 4 log cycles and yielded the highest amount (41.1 μg/ml) of aflatoxin B₁ in AMMB. However, moist heat treatment of spores receiving the same dose (3.5 kGy) reduced toxin level formed by 25%. Aflatoxin B₁ formation by A. flavus spores incubated in AMMB was completely prevented by a combination treatment of moist heat and 4.0 kGy of gamma irradiation. This same treatment attenuated aflatoxins B₂, G₁ and G₂ production which are formed with B₁ by A. flavus NRRL 5906. Spores raised in all flasks containing MMB did not form aflatoxin except when the medium MMB was autoclaved twice at 121°C for 15 min.     

Delivery systems for biological control agents to manage aflatoxin contamination of pre-harvest maize

While soil application of a competitive non-toxigenic Aspergillus flavus strains is successful in reducing aflatoxin contamination in certain crops, direct application to aerial reproductive structures could be more effective for maize. A sprayable, clay-based water-dispersible granule formulation was developed to deliver non-toxigenic A. flavus strain K49 directly to maize ears. The efficacy of the K49 water-dispersible granule in mitigating aflatoxin in maize (Zea mays L.) was evaluated. Field studies were conducted to compare K49 colonization and effectiveness in reducing aflatoxin contamination when applied either as a soil inoculant or as a directed spray in plots infested with toxigenic strain F3W4. Fifty percent of non-toxigenic A. flavus was recovered from non-treated controls and from plots soil inoculated with K49 on wheat. In spray treatments with formulated or unformulated K49 conidia, over 90% of A. flavus recovered was non-toxigenic. Soil-applied K49 reduced aflatoxin contamination by 65% and spray applications reduced contamination by 97%. These findings suggest direct spray application of non-toxigenic A. flavus strains may be better than soil inoculation at controlling maize aflatoxin contamination and that a water-dispersible granule is a viable delivery system for maintaining viability and efficacy of the biological control agent, K49.     

Influence of γ‐irradiation and maize lipids on the production of aflatoxin B1 by Aspergillus flavus

The effect of γ‐irradiation and maize lipids on aflatoxin B₁ production by Aspergillus flavus artificially inoculated into sterilized maize at reduced water activity (a_w 0.84) was investigated. By increasing the irradiation doses the total viable population of A. flavus decreased and the fungus was completely inhibited at 3.0 kGy. The amounts of aflatoxin B₁ were enhanced at irradiation dose levels 1.0 and 1.5 kGy in both full‐fat maize (FM) and defatted maize (DM) media and no aflatoxin B₁ production at 3.0 kGy γ‐irradiation over 45 days of storage was observed. The level in free lipids of FM decreased gradually, whereas free fatty acid values and fungal lipase activity increased markedly by increasing the storage periods. The free fatty acid values decreased by increasing the irradiation dose levels and there was a significant enhancement of fungal lipase activity at doses of 1.0 and 1.50 kGy. The ability of A. flavus to grow at a_w 0.84 and produce aflatoxin B₁ is related to the lipid composition of maize. The enhancement of aflatoxin B₁ at low doses was correlated to the enhancement of fungal lipase activity.     

Moisture-equilibrium relative humidity relationships in pistachio nuts with particular regard to control of aflatoxin formation

Adsorption and desorption isotherms have been determined both manometrically and by weight equilibration for Turkish pistachio nut kernel, shell and hull. Comparison of the calculated and experimentally determined adsorption isotherms for whole nuts showed good correlation. Nuts inoculated with Aspergillus flavus conidia were equilibrated to various ERH levels and stored in controlled environment cabinets at 28°C. Competitive growth of xerophilic strains of A. amstelodami prevented growth and aflatoxin production by the A. flavus at ERHs of 86% and below. At 88% ERH marked aflatoxin production occurred but competition was observed between the A. flavus and A. niger. In sealed containers metabolic moisture from growth of A. amstelodami raised the ERH from the initial 85% and permitted toxin production by A. flavus. The results are discussed in relation to post-harvest handling and storage of pistachio nuts.     

Effect of Cycling Temperatures on Aflatoxin Production by Aspergillus parasiticus and Aspergillus flavus in Rice and Cheddar Cheese

Initiation of growth, sporulation and aflatoxin production at cycling temperatures took less time than at 15°C but more than at 18°C and 25°C. A. parasiticus produced more aflatoxins on rice under cycling temperatures than at 25°C, 18°C or 15°C, while A. flavus produced less aflatoxin under cycling temperatures. A. parasiticus produced more aflatoxins on cheese under cycling temperatures than at 18°C or 15°C, but much less than at 25°C. A. flavus produced less aflatoxins on cheese under cycling temperatures than at 18°C and 25°C. Both organisms produced trace amounts of toxins at 15°C on cheese. Preincubation at 25°C for 2 days before temperature cycling did not increase aflatoxin production on rice but increased production on cheese. The rate of aflatoxin production on cheese decreased as the temperature decreased. No growth, sporulation or aflatoxin production was observed at 5°C on either rice or cheese.     

Aspergillus flavus infection and aflatoxin production in mixtures of high-moisture and dry maize

High-moisture (26·6–27·9% m.c.) and dry (9·8% m.c.) fractions of white and yellow maize were examined for fungal development and aflatoxin production during an 8-week incubation at 25°C. Treatment procedures included blending of either high-moisture white with dry yellow or high-moisture yellow with dry white maize fractions (average moisture in blend, 14%) and inoculation of some test maizes with A. flavus spores. At sampling time white and yellow components of maize blends were manually separated and all of the maize samples were analyzed for levels of moisture, fungal infection and aflatoxin. Moisture levels in maize blends equilibrated rapidly during the initial 2–4 days of incubation; neither dry yellow nor dry white exceeded 13% moisture during the trial period. Only a limited incidence of A. flavus was observed on uninoculated maize. but in samples treated with A. flavus spores a high infection rate developed; from 58 to 98% of the kernels in dry fractions of inoculated blends were infected with A. flavus during the trial. Aflatoxin was detected in high-moisture maize and in both high-moisture and dry fractions of inoculated maize blends. Up to 500 μg aflatoxin B₁/kg of corn was found after the 8-week incubation in a dry fraction of inoculated maize blends.     

Influence of white light,near-UV irradiation and other environmental conditions on production of aflatoxin B1 by Aspergillus flavus and ochratoxin A by Aspergillus ochraceus

The effects of illumination, near-ultraviolet, incubation temperature pH and some minor elements on the growth rate and production of aflatoxin B₁ by A. flavus and ochratoxin A by A. ochraceus were investigated. Aflatoxin B₁ and ochratoxin A production was considerably higher in the light than in the dark. The greatest aflatoxin B₁ and ochratoxin A production was occurred after 11 days of fermentation with light- and dark-grown cultures at 25 °C. The mycelial dry weight was also greater in the light than in the dark for both A. flavus and A. ochraceus. Exposure of conidia to near-UV irradiation increased mycelial dry weight and mycotoxins by both fungi more than white light. The greatest aflatoxin B₁ and ochratoxin A was at 25 °C with UV-grown culture (24 h exposure) producing a mean of 400 and 260 μg/50 ml of medium, respectively. The maximum aflatoxin B₁ and ochratoxin A yield was obtained at pH 5.5 and with increasing the initial pH to near neutrality, both mycotoxins yield decreased. Iron, cupper and zinc were observed to stimulate aflatoxin B₁ and ochratoxin A production and enhanced the growth rate of both A. flavus and A. ochraceus.     

Effect of CO2 modified atmosphere packaging on aflatoxin production in maize infested with Sitophilus zeamais

The weevil Sitophilus zeamais (Motschulsky), the maize weevil, is a pest of stored maize that can cause feeding damage and lead to the proliferation of toxigenic fungi. The application of modified atmospheres with a high concentration of CO₂ is an alternative method for the control of S. zeamais and the inhibition of fungal growth. The objectives of the study were to determine the effect of S. zeamais infestation, grain damage and grain moisture content on aflatoxin production by Aspergillus flavus on maize, and the impact of high CO₂ modified atmosphere packaging on pest infestation and aflatoxin production. Mycotoxin production was only recorded when maize was infested with S. zeamais and had A. flavus inoculum. However, production of mycotoxins was not recorded when the maize was mechanically damaged and stored at 18% moisture content, indicating that the biological activity of the insect was determinant in the production of mycotoxins. The high CO₂ modified atmosphere packaging tested (90% CO₂, 5% O₂ and 5% N₂) prevented mycotoxin production.     

Effects of Tropical Citrus Essential Oils on Growth, Aflatoxin Production, and Ultrastructure Alterations of Aspergillus flavus and Aspergillus parasiticus

Ethyl acetate extracts and hydrodistillated essential oils from five cultivars of tropical citrus epicarps were evaluated for their inhibitory activities against Aspergillus fumigatus, Aspergillus niger, Aspergillus flavus, Aspergillus parasiticus, and Penicillium sp. using disk diffusion and broth microdilution assays. Essential oils prepared from kaffir lime (Citrus hystrix DC) and acid lime (Citrus aurantifolia Swingle) epicarps exhibited stronger antifungal activity to all fungi than their ethyl acetate extracts with minimum inhibitory concentration and minimum fungicidal concentration values of 0.56 and 1.13 mg/ml (dry matter), respectively, against aflatoxin-producing A. flavus and A. parasiticus. The dominant components of the essential oil from kaffir lime were limonene, citronellol, linalool, o-cymene, and camphene, whereas limonene and p-cymene were major components of acid lime essential oil. Pure limonene, citronellal, and citronellol were five to six times less fungicidal than the natural essential oils, indicating the synergistic activity of many active compounds present in the oils. Kaffir and acid lime essential oils significantly reduced aflatoxin production of A. flavus and A. parasiticus, particularly lime essential oil, which completely inhibited growth and aflatoxin production of A. flavus at the concentration of 2.25 mg/ml. Target cell damage caused by acid lime essential oil was investigated under transmission electron microscopy. Destructive alterations of plasma and nucleus membrane, loss of cytoplasm, vacuole fusion, and detachment of fibrillar layer were clearly exhibited in essential-oil-treated cells.     

Antifungal properties and inhibitory effects upon aflatoxin production by Zingiber officinale essential oil in Aspergillus flavus

In this study, the efficacy of ginger (Zingiber officinale Roscoe) essential oil (GEO) in reducing A. flavus growth and aflatoxin production was investigated. Gas chromatography coupled to mass spectrometry and nuclear magnetic resonance spectroscopy showed that the major components of GEO were α‐zingiberene (23.85%) and geranial (14.16%). Mycelial growth of Aspergillus flavus was reduced significantly at a GEO concentration of 150 μg mL^?1, and complete inhibition of conidial germination was observed at a concentration of 10 μg mL^?1. Statistically significant inhibition of ergosterol biosynthesis was detected at a GEO concentration of 10 μg mL^?1. GEO was capable of fully inhibiting aflatoxin production by A. flavus at a concentration of 15 μg mL^?1. The results suggest that low concentrations of GEO are capable of inhibiting aflatoxin production; such ability could be valuable in the upcoming future for agricultural companies to better control aflatoxigenic fungi in agricultural products.     

Modeling Growth Rate and Assessing Aflatoxins Production by Aspergillus flavus as a Function of Water Activity and Temperature on Polished and Brown Rice

Abstract: The aim of this study was to model the radial growth rate and to assess aflatoxin production by Aspergillus flavus as a function of water activity (a_w 0.82 to 0.92) and temperature (12 to 42 °C) on polished and brown rice. The growth of the fungi, expressed as colony diameter (mm) was measured daily, and the aflatoxins were analyzed using HPLC with a fluorescence detector. The growth rates were estimated using the primary model of Baranyi, which describes the change in colony radius as a function of time. Total of 2 secondary models were used to describe the combined effects of a_w and temperature on the growth rates. The models were validated using independent experimental data. Linear Arrhenius–Davey model proved to be the best predictor of A. flavus growth rates on polished and brown rice followed by polynomial model. The estimated optimal growth temperature was around 30 °C. A. flavus growth and aflatoxins were not detected at 0.82 a_w on polished rice while growth and aflatoxins were detected at this a_w between 25 and 35 °C on brown rice. The highest amounts of toxins were formed at the highest a_w values (0.90 to 0.92) at a temperature of 20 °C after 21 d of incubation on both types of rice. Nevertheless, the consistencies of toxin production within a wider range of a_w values occurred between 25 to 30 °C. Brown rice seems to support A. flavus growth and aflatoxin production more than the polished rice. Practical Application: The developed models can be used to estimate to what extent the change in grain ecosystem conditions affect the storage stability and safety of grains without the need for running long‐standing storage study. By monitoring the intergranular relative humidity and temperature at different locations in the storage facility and inputting these data into the models, it is directly possible to assess either the conditions are conductive for the growth of A. flavus or aflatoxin production.