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.     

Assessing Purdue Improved Crop Storage (PICS) bags to mitigate fungal growth and aflatoxin contamination

Storing maize in regions of the world without sufficient drying and storage capacity is challenging due to the potential risk of aflatoxin contamination produced by Aspergillus flavus. This study sought to determine if storage of maize in Purdue Improved Crop Storage (PICS) bags prevents mold growth and aflatoxin accumulation. PICS bags are a three-layer, hermitic bag-system that forms a barrier against the influx of oxygen and the escape of carbon dioxide. Maize conditioned at 12, 15, 18, and 21% grain moisture was inoculated with 50 g of maize kernels infected with fluorescent-marked strain of A. flavus. The grain was stored in either PICS or woven bags at 26 °C, and percent oxygen/carbon dioxide levels, fungal growth, aflatoxin, moisture content, and kernel germination were assessed after 1 and 2 months incubation. Maize stored in woven bags was found to equilibrate with the ambient moisture environment over both storage periods, while PICS bags retained their original moisture levels. Aspergillus flavus growth and aflatoxin accumulation were not observed in maize stored in any PICS bags. No aflatoxin B1 was detected in woven bags containing low-moisture maize (12 and 15%), but detectable levels of aflatoxin were observed in high moisture maize (18 and 21%). The percentage of oxygen and carbon dioxide within PICS bags were dependent on initial grain moisture. Higher carbon dioxide levels were observed in the bags stored for 1 month than for 2 months. High initial moisture and carbon dioxide levels correlated with low kernel germination, with the 18 and 21% treatment groups having no seeds germinate. The results of the study demonstrate that storage of maize in PICS bags is a viable management tool for preventing aflatoxin accumulation in storage.     

Fungi and aflatoxin in a bin of stored white maize

Samples of maize from discolored spots in the surface layer of stored grain in a southeast Missouri bin were examined for variation in microbial profile and for the presence of aflatoxin. Comparisons were made with samples of non-discolored maize from the same bin. Deteriorated test kernels showed a high incidence of Penicillium, Absidia, Mucor, Rhizopus and Fusarium spp., as well as bacteria and yeasts. Aspergillus species were also frequently observed; A. flavus was the most common species in this group. In one sample of discolored maize 80 per cent of the kernels contained A. flavus and the sample had 0·40 ppm aflatoxin B₁. Other fractions exhibited extensive discoloration but no aflatoxin.     

Aspergillus flavus and aflatoxin production in acid-treated maize

Isobutyric acid (IBA) and propionic-acetic acid (PA) were applied to comparable 52.8 m³ lots of freshly harvested yellow dent maize containing 27% moisture. After 6 months storage, 30% Aspergillus flavus infection and low levels of aflatoxin were detected in adjacent bins of IBA-treated and PA-treated maize. Extensive samples were taken after 7 months from moldy spots in each bin and evaluated for aflatoxin, zearalenone, ochratoxin and microorganisms. Aspergillus flavus (10⁶ propagules/g) was detected in 40% of the PA samples, but no aflatoxin was found. Also, counts of Aspergillus fumigatus, Absidia and Penicillia were high. In addition to the molds found on PA maize, Aspergillus niger was identified on IBA-treated maize. Aspergillus flavus (10⁴–10⁷ propagules/g) was present in 79% of the IBA samples; aflatoxin (from 2 to 857 ng/g) was detected in 57%. Aflatoxin contamination varied between locations within a moldy area. Among 20 individual kernels picked at random from each location, aflatoxin contamination ranged from 150 to 21.800 ng/g in positive kernels. Evidently, bulk quantities of maize must be appraised on the basis of individual kernels because toxin-free kernels often are adjacent to highly contaminated kernels.     

Spread of Aspergillus flavus and aflatoxin accumulation in postharvested maize treated with biocontrol products

Maize is a major staple crop and calorie source for many people living in Sub-Saharan Africa. In this region, Aspergillus flavus causes ear rot in maize, contributing to food insecurity due to aflatoxin contamination. The biological control principle of competitive exclusion has been applied in both the United States and Africa to reduce aflatoxin levels in maize grain at harvest by introducing atoxigenic strains that out-compete toxigenic strains. The goal of this study was to determine if the efficacy of preharvest biocontrol treatments carry over into the postharvest drying period, the time between harvest and the point when grain moisture is safe for storage. In Sub-Sahara Africa, this period often is extended by weather and the complexities of postharvest drying practices. Maize grain was collected from fields in Texas and North Carolina that were treated with commercial biocontrol products and untreated control fields. To simulate moisture conditions similar to those experienced by farmers during drying in Sub-Sahara Africa, we adjusted the grain to 20% moisture content and incubated it at 28 °C for 6 days. Although the initial number of kernels infected by fungal species was high in most samples, less than 24% of kernels were infected with Aspergillus flavus and aflatoxin levels were low (<4 ppb). Both toxigenic and atoxigenic strains grew and spread through the grain over the incubation period, and aflatoxin levels increased, even in samples from biocontrol-treated fields. Our molecular analysis suggests that applied biocontrol strains from treated fields may have migrated to untreated fields. These results also indicate that the population of toxigenic A. flavus in the harvested grain will increase and produce aflatoxin during the drying period when moisture is high. Therefore, we conclude that preharvest biocontrol applications will not replace the need for better postharvest practices that reduce the drying time between harvest and storage.     

Aflatoxins’ fate during the nixtamalization of contaminated maize by two tortilla-making processes

The fate of aflatoxin B₁ and B₂ was studied during maize nixtamalization by two tortilla-making processes. High-quality maize seed (AS-900) was used, as well as a toxigenic strain of Aspergillus flavus. The grain moisture content was adjusted to 18%, and the incubation temperature was 27°C. One lot of grain served as the control and so was not inoculated with the fungus. At the end of the 13 d incubation period, this control lot was aflatoxin free (aflatoxin level 1). Two other lots were inoculated with the fungus and incubated for 12 and 14 d. They then had aflatoxin contamination of 29 and 93 ppb, respectively (aflatoxins levels 2 and 3). The quantification of aflatoxins was undertaken according to the AOAC Official Method 991.31 and their identification confirmed by HPLC. The maize grain was processed by the traditional (TNP) and the ecological (ENP) nixtamalization processes. Aflatoxins were quantified at all steps of the tortilla-making processes. The research was conducted under a completely randomized factorial design (2×3). In the case of tortillas processed with TNP, the total aflatoxin content was 2 and 9 ppb corresponding to aflatoxin levels 2 and 3 with a degradation rate of 92% and 90%, respectively. In tortillas obtained through the ENP, the aflatoxin content was 6 and 36 ppb for aflatoxin levels 2 and 3, with degradation rates of 78% and 61%, respectively. The TNP produced higher aflatoxin degradation rates than the ENP.     

Influence of storage environment on maize grain: CO2 production,dry matter losses and aflatoxins contamination

Poor storage of cereals, such as maize can lead to both nutritional losses and mycotoxin contamination. The aim of this study was to examine the respiration of maize either naturally contaminated or inoculated with Aspergillus flavus to examine whether this might be an early and sensitive indicator of aflatoxin (AF) contamination and relative storability risk. We thus examined the relationship between different interacting storage environmental conditions (0.80–0.99 water activity (a_w) and 15–35°C) in naturally contaminated and irradiated maize grain + A. flavus on relative respiration rates (R), dry matter losses (DMLs) and aflatoxin B1 and B2 (AFB1-B2) contamination. Temporal respiration and total CO₂ production were analysed by GC-TCD, and results used to calculate the DMLs due to colonisation. AFs contamination was quantified at the end of the storage period by HPLC MS/MS. The highest respiration rates occurred at 0.95 a_w and 30–35°C representing between 0.5% and 18% DMLs. Optimum AFs contamination was at the same a_w at 30°C. Highest AFs contamination occurred in maize colonised only by A. flavus. A significant positive correlation between % DMLs and AFB1 contamination was obtained (r = 0.866, p < 0.001) in the irradiated maize treatments inoculated with A. flavus. In naturally contaminated maize + A. flavus inoculum loss of only 0.56% DML resulted in AFB1 contamination levels exceeding the EU legislative limits for food. This suggests that there is a very low threshold tolerance during storage of maize to minimise AFB1 contamination. This data can be used to develop models that can be effectively used in enhancing management for storage of maize to minimise risks of mycotoxin contamination.     

Physical factors in the hermetic SuperGrainBag® and effect on the larger grain borer [Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)] and aflatoxin production by Aspergillus flavus during the storage of ‘Obatanpa’ maize (Zea mays L.) variety

Controlling invasive pests and aflatoxin production by moulds in stored grains is a global challenge to food security and public health, particularly in Africa. Food storage systems are designed to provide constraints to spoilage organisms by presenting mechanical barrier or unfavourable atmospheric conditions to their growth and productivity. This study examined the physical factors generated in hermetic SuperGrainBags^® during the storage of ‘Obatanpa’ variety of maize (Zea mays L.) and the effect on growth of the larger grain borer Prostephanus truncatus (Horn) and aflatoxin contamination by Aspergillus flavus. Cultured P. truncatus or A. flavus was introduced into 1.5 kg of the dried maize and stored in either hermetic SuperGrainBags^® or non-hermetic polypropylene bags. The hermetic conditions elicited an increase in the interstitial temperature (ca. 27 °C) but a decrease in the relative humidity (<70%), oxygen concentration (<6.4%) and the grain moisture content (<13.7%), the combined effects of which inhibited growth of the insects and aflatoxin production by the moulds. Total mortality of P. truncatus occurred after 52 d of storage in the SuperGrainBags^® while aflatoxins concentration remained within safe limits for human consumption. In contrast, there was proliferous growth of P. truncatus and significant increase in aflatoxin concentration to lethargic levels within the polypropylene bags where temperature, relative humidity and grain moisture increased significantly. Accordingly, grain damage and weight loss percentages were significantly high in the polypropylene bags while that in the SuperGrainBags^® were negligible. Altogether, the SuperGrainBags^® better preserved the maize grain quality and safeguarded it against health risks than the polypropylene bags.     

Effect of sublethal concentrations of propionic or butyric acid on growth and aflatoxin production by Aspergillus flavus

Propionic or butyric acid was added at sublethal doses (0.1–2 mg/ml) to a growth medium supporting growth of Aspergillus flavus and subsequent aflatoxin production. A reduction in growth and aflatoxin production occurred when the acids were added at the time of inoculation. Addition of the acids to cultures at different times resulted in little effect on growth but production of aflatoxin after 12 days was reduced with earlier time of application for both propionic and butyric acid. When the acids were added to rough rice with a moisture content of 21% and inoculated with A. flavus fungal growth and aflatoxin production were reduced relative to non-inoculated controls. Early application of acids resulted in lower yields of aflatoxin.     

Impact of opening hermetic storage bags on grain quality,fungal growth and aflatoxin accumulation

Purdue Improved Crop Storage (PICS) bags are used by farmers in Sub-Saharan Africa for pest management of stored grains and products, including maize. These bags hermetically seal the products, preventing exchange with external moisture and gases. Biological respiration within the bags create an environment that is unsuitable for insect development and fungal growth. This study was conducted to determine the impact of routine opening of the storage bags for maize consumption on fungal growth and aflatoxin contamination. Maize with moisture contents (MC) high enough to support fungal growth (15%, 16%, 18% and 20%) was stored in PICS bags, which were opened weekly and exposed to humid conditions (85% RH) for 30 min over a period of 8 weeks and 24 weeks. Monitors indicated that oxygen defused into the open bags but did not reach equilibrium with the bottom layers of grain during the 30-min exposure period. Fungal colony forming units obtained from the grain surface increased 3-fold (at 15% MC) to 10,000-fold (at 20% MC) after 8 weeks. At both 8 weeks and 24 weeks, aflatoxin was detected in at least one bag at each grain moisture, suggesting that aflatoxin contamination spread from a planted source of A. flavus-colonized grain to non-inoculated grain. The results indicate that repeatedly breaking the hermetic seal of the PICS bags will increase fungal growth and the risk of aflatoxin contamination, especially in maize stored at high moisture content. This work also further demonstrates that maize should be properly dried prior to storage in PICS bags.     

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.     

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.     

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.     

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.     

Moisture content,insect pest infestation and mycotoxin levels of maize in markets in the northern region of Ghana

Reliable quantitative data on maize post-harvest losses and factors that cause them in northern Ghana are limited. In this study we assessed maize at six markets in the Northern Region of Ghana, in and around Tamale, during the harvest and storage period of October 2015–June 2016. Across all the markets and sampling periods grain temperature was 32.6 ± 0.2 °C and equilibrium moisture content (EMC) was 9.5 ± 0.2%. EMC tended to decrease to a low in January and February and then increased again, while mean maize temperature was above 30 °C in all months. The primary stored product insects collected from the samples were Tribolium castaneum (Herbst), Sitophilus spp., Rhyzopertha dominica (Fauvel), and Cryptolestes ferrugineus (Stephens). Using all the market and sampling month data, there was a significant correlation between EMC and total number of insects recovered, but not between total number of insects and temperature. The average percentage of insect-damaged kernels (IDK) in the maize sampled across all the markets and sampling periods was 2.7 ± 0.2%, with a range between 0 and 21.4%. Using all the market and sampling month data, levels of insect damage tended to be positively correlated with maize moisture, but not temperature, and levels of insect damage increased with number of stored product insects recovered. The action threshold for aflatoxin in maize in Ghana is 15 ppb, but overall mean aflatoxin level was 19.8 ± 1.5 ppb and aflatoxin levels ranged from 0.3 to 132.2 ppb, with 53% of the samples having levels above 15 ppb. The mean fumonisin level was 1.2 ± 0.0 ppm, which is below the 4.0 ppm action threshold for Ghana. Our results show that aflatoxin levels were high in the market maize in Northern Region of Ghana and insects were prevalent, even though grain moisture tended to be relatively low, especially compared to the Middle Belt of Ghana.     

Comparison of dry matter losses and aflatoxin B1 contamination of paddy and brown rice stored naturally or after inoculation with Aspergillus flavus at different environmental conditions

The objective of this study was to compare the effect of different storage moisture conditions (0.70, 0.85, 0.90 and 0.95 water activity, a_w) and temperatures (20, 25, 30 °C) on (a) respiration rates (R) and dry matter loss (DML) of paddy and brown rice and (b) quantify aflatoxin B₁ (AFB₁) production by isolates of Aspergillus flavus from the rice samples and (c) inoculation of both rice types with A. flavus under these storage conditions on R, DML and AFB₁ contamination. There was an increase in temporal CO₂ production with wetter and warmer conditions in naturally contaminated rice. Higher R and consequently, % DML, were generally found in the brown rice (21%) while in paddy rice this was only up to 3.5% DML. From both rice types, 15 (83.3%) of 18 A. flavus isolates produced detectable levels of AFB₁ in a range 2.5–1979.6 μg/kg. There was an increase in DML in both rice types inoculated with A. flavus as temperature and a_w were increased. Interestingly very little AFB₁ was detected in paddy rice, but significant contamination occurred in the brown rice. The %DML in the control and A. flavus inoculated rice increased with temperature and a_w at both 25 and 30 °C from 1-2% to 15–20% DML at 30 °C and 0.95 a_w. All the inoculated rice samples had AFB₁ levels above the EU legislative limits for contamination in other temperate cereals and products derived from cereals (=2 μg/kg). Even samples with % DML as low as 0.2% had AFB₁ contamination levels twice the limits for other cereals. These results suggest that the mycotoxin contamination risk in staple commodities like rice, is influenced by whether the rice is processed or not, and that measurement of R rates can be used to predict the relative risk of AFB₁ contamination in such staple commodities.     

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.     

Aflatoxin contents of stored and artificially inoculated cereals and nuts

Aflatoxin contents of cereals and nuts, collected from local markets of NWFP, were determined by thin layer chromatography (TLC). The seeds of these crops were also inoculated with Aspergillus flavus and the aflatoxin content and its relation with the proximate composition of seeds was studied. The effect of storage for different durations of time (2–3 and 12–18 months) on the aflatoxin content of seeds was also assessed. Aflatoxin content of cereals (wheat, maize and rice) ranged from 14 to 45 μg/kg, and that of nuts (almond, walnut and peanut) varied from 5 to 17 μg/kg. The aflatoxin content was within the safe limit (50 μg/kg) recommended by FAO. The aflatoxin content of inoculated seeds was significantly (p < 0.05) increased over control (un-inoculated seeds). This was positively related (r = 0.65) to moisture content of the seeds. However, negative correlation (r = −0.50) existed between aflatoxin and ash contents of the seeds. Protein, fat and total carbohydrate (NFE) contents were not much affected by inoculation. Prolonged storage for 18 months (1.5 years) significantly (p < 0.05) increased aflatoxin contents of seeds compared to short storage periods (2–3 months). It was concluded that aflatoxin content of food should be monitored to ensure food safety. Prolonged storage of cereal and nuts in warm humid condition should be avoided to minimize the risk of aflatoxin contamination.     

Effect of gamma irradiation and heat treatment on the artificial contamination of maize grains by Aspergillus flavus Link NRRL 5906

Maize (Zea mays L.) is one of the main crops, which is easily susceptable to Aspergillus flavus infection resulting in huge losses worldwide. This study was carried out to investigate the effect of combining heat and irradiation treatments in controlling the fungal growth in maize grains. Surface disinfected maize grains were artificially contaminated with spores of Aspergillus flavus Link NRRL 5906, and then exposed to gamma radiation with doses of 3.0, 4.0 and 5.0 kGy. The samples were additionally heat treated at 60 °C for 30 min. The heat and irradiation treatments showed a synergistic effect on controlling Aspergillus flavus growth. The heat treatment reduced the required radiation dose of about 0.5–1.0 kGy when 4.0 kGy or 5.0 kGy irradiation was used. The combined heat and irradiation treatment of moisture reduced the average CFU by 8 log cycles when 4 kGy or 5 kGy irradiation was used and by 7 log cycles when 3 kGy irradiation was used. The heat treatment of moisture alone reduced the average CFU by only by 0.8 log cycles. Combining irradiation with heat treatment to reduce the required radiation dose is very useful especially when there is a concern over biological side effects of irradiation.