Influence of gamma-irradiation and maize lipids on the production of aflatoxin B1 by Aspergillus flavus

The effect of gamma-irradiation and maize lipids on aflatoxin B1 production by Aspergillus flavus artificially inoculated into sterilized maize at reduced water activity (aw 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 gamma-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 aw 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.     

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.     

Inhibition by gamma-irradiation and antimicrobial food additives of aflatoxin B1 production by Aspergillus flavus in poultry diet

The effect of gamma-irradiation and the antimicrobial food additives on growth and aflatoxin B₁ production by A. flavus NRRL 5520 in poultry diet was investigated. By increasing the irradiation doses the viable population as well as aflatoxin B₁ production decreased greatly. No growth and no detection of aflatoxin production occurred in poultry diet after treatment with 6 kGy. The addition of the antimicrobial food additives resulted in a significant decrease in aflatoxin B₁. Growth and toxin production was completely inhibited by 0.64% sodium propionate, 0.134% potassium sorbate and 0.1% sodium bisulfite. The combination treatments between gamma-irradiation (3 kGy) and sodium propionate (0.48%), potassium sorbate (0.022% and 0.044%) and sodium bisulfite (0.0334% and 0.0667%) inhibited completely the fungal growth and aflatoxin B₁ production. At 5 kGy, no growth was recorded and aflatoxin B₁ production was completely inhibited at all tested levels of priopionate, sorbate and bisulfite. The combined effects between gamma-irradiation and the antimicrobial agents had a synergistic effect on the mould growth and aflatoxin production in poultry diet.     

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.     

Incidence of aflatoxin B1 in the Egyptain cured meat basterma and control by γ‐irradiation

In the present studies trials have been carried out to investigate the occurrence of aflatoxin B₁ in the Egyptian cured meat basterma and to control such contamination by γ‐rays. Basterma was prepared from fresh salted meat coated with spice paste and stored at room temperature. The total mould counts of basterma samples varied from 10³ to 10⁶ cfu/g in summer months and from 10² to 10⁵ cfu/g in winter months. Aspergillus, Penicillium, Mucor, Rhizopus, Fusarium and Cladosporium were the most common fungal genera isolated from basterma samples and its components. Basterma samples contained total aflatoxins at levels from 2.8 to 47 μg·kg^–1. Aflatoxins were determined in the spice paste at levels from 9.6 to 120 μg·kg^–1 and in pepper (285.6 μg·kg^–1), garlic (224.4 μg·kg^–1), fenugreek (194.2 μg·kg^–1), coriander (166.4 μg·kg^–1) and capsicum (42.4 μg·kg^–1). At an irradiation dose level of 3 kGy, only one sample each of pepper, fenugreek, and spice paste were contaminated with aflatoxins and all basterma samples and its components were free from aflatoxins at an irradiation dose level of 5 kGy.     

Physical,functional and pasting properties of different maize (Zea mays) cultivars as modified by an increase in γ‐irradiation doses

Physical, functional and pasting properties of six maize (Zea mays) cultivars as modified by an increase in γ‐irradiation doses were investigated. From the L*, a* and b* measured, deltachroma, colour intensity and hue angle were calculated. Functional and physicochemical properties of maize flours were determined using standard methods and Rapid Visco Analyser, respectively. Often, the effect of γ‐irradiation on L*, a* and b* values within each cultivar was almost never significant but pronounced between the yellow and white cultivars. Generally, deltachroma, colour intensity and hue angle decreased with increased γ‐irradiation dose. Mean seed bulk density and 100 kernel weight varied from 0.73–0.77 g cm^?3 and 23.13–35.42 g, respectively. Loose and packed bulk densities, and water (WAC) and oil absorption capacities of the maize flours were not significantly affected by γ‐irradiation. WAC of nonirradiated and γ‐irradiated maize flours ranged from 1.54–1.62 and 1.09–1.70 g g^?1, respectively. Peak, trough, breakdown, final and setback viscosities decreased significantly (P < 0.05) with increased γ‐irradiation dose.     

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.     

Potential use of phenolic antioxidants on peanut to control growth and aflatoxin B1 accumulation by Aspergillus flavus and Aspergillus parasiticus

Food‐grade antioxidants: butylated hydroxyanisole (BHA), propyl paraben (PP) and butylated hydroxytoluene (BHT) (10 and 20 mmol g^?1) and all the mixtures of these chemicals were tested for inhibitory activity on the growth of and aflatoxin B₁ (AFB₁) accumulation by Aspergillus parasiticus and A. flavus on irradiated (7 kGy) peanut grains. Also, the influence of these treatments was evaluated in different water conditions (0.982, 0.955, 0.937a_w) at 11 and 35 days of incubation at 28 °C. Water activity (a_w) affected the fungal growth, no fungal development was observed at the highest stress water condition (0.937a_w). Butylated hydroxyanisole at 10 mmol g^?1 level and all the mixtures with PP and/or BHT were significantly effective (P = 0.05) in increasing lag phase and reducing growth rate and colony forming units per gram of peanut of both Aspergillus section Flavi strains and AFB₁ accumulation. The application of BHA at concentrations of 20 mmol g^?1 alone or with PP and/or BHT totally inhibited fungal growth at 11 and 35 days of incubation. The results suggest that the addition of these chemical mixtures on peanut grains at low levels has potential to impact synergically on the control of Aspergillus section Flavi. Copyright © 2007 Society of Chemical Industry     

Assessment of azole fungicides as a tool to control growth of Aspergillus flavus and aflatoxin B1 and B2 production in maize

ABSTRACT

Aspergillus flavus is a highly aflatoxin (AF)-producing species infecting maize and other crops. It is dominant in tropical regions, but it is also considered an emerging problem associated with climate change in Europe. The aim of this study was to assess the efficacy of azole fungicides (prochloraz, tebuconazole and a 2:1 (w/w) mixture of prochloraz plus tebuconazole) to control the growth of A. flavus and AF production in yeast-extract–sucrose (YES) agar and in maize kernels under different water activities (a_w) and temperatures. Aflatoxins B₁ and B₂ were determined by LC with fluorescence detection and post-column derivatisation of AFB₁. In YES medium and maize grains inoculated with conidia of A. flavus, the growth rate (GR) of the fungus and AFB₁ and AFB₂ production were significantly influenced by temperature and treatment. In YES medium and maize kernels, optimal temperatures for GR and AF production were 37 and 25°C, respectively. In maize kernels, spore germination was not detected at the combination 37ºC/0.95 a_w; however, under these conditions germination was found in YES medium. All fungicides were more effective at 0.99 than 0.95 a_w, and at 37 than 25ºC. Fungicides effectiveness was prochloraz > prochloraz plus tebuconazole (2:1) > tebuconazole. AFs were not detected in cultures containing the highest fungicide doses, and only very low AF levels were found in cultures containing 0.1 mg l^–1 prochloraz or 5.0 mg l^–1 tebuconazole. Azoles proved to be highly efficient in reducing A. flavus growth and AF production, although stimulation of AF production was found under particular conditions and low-dosage treatments. Maize kernels were a more favourable substrate for AF biosynthesis than YES medium. This paper is the first comparative study on the effects of different azole formulations against A. flavus and AF production in a semi-synthetic medium and in maize grain under different environmental conditions.     

Shelf‐life extension of vacuum‐packaged sea bream (Sparus aurata) fillets by combined γ‐irradiation and refrigeration: microbiological,chemical and sensory changes

The combined effect of γ‐irradiation and refrigeration on the shelf‐life of vacuum‐packaged sea bream (Sparus aurata) fillets was studied by monitoring the microbiological, chemical and sensory changes of non‐irradiated and irradiated fish samples using low‐dose irradiation doses of 1 and 3 kGy. Fish species such as sea bream and sea bass are very popular in the Mediterranean countries due to their high quality characteristics, and their preservation is a constant challenge given their extreme perishability. Irradiation (3 kGy) dramatically reduced populations of bacteria, namely, total viable counts (3 vs 7 log cfu g^?1) for the non‐irradiated samples, Pseudomonas spp (<2 vs 7.6 log cfu g^?1), H₂S‐producing bacteria typical of Shewanella putrefaciens (<2 vs 5.9 log cfu g^?1), Enterobacteriaceae (<2 vs 6.0 log cfu g^?1) and lactic acid bacteria (<2 vs 3.5 log cfu g^?1) after 10 days of storage. The effect was more pronounced at the higher dose (3 kGy). Lactic acid bacteria, Enterobacteriaceae and H₂S‐producing bacteria typical of Shewanella putrefaciens showed higher sensitivity to γ‐radiation than did the rest of the microbial species. Of the chemical indicators of spoilage, Trimethylamine (TMA) values of non‐irradiated sea bream increased very slowly, whereas for irradiated samples significantly lower values were obtained reaching a final value of 7.9 and 6.3 mg N per 100 g muscle at 1 and 3 kGy respectively (day 42). Total volatile basic nitrogen (TVB‐N) values increased slowly attaining a value of 67.3 mg N per 100 g for non‐irradiated sea bream during refrigerated storage, whereas for irradiated fish, lower values of 52.8 and 43.1 mg N per 100 g muscle were recorded (day 42). Thiobarbituric acid (TBA) values for irradiated sea bream samples were higher than respective non‐irradiated fish and increased slowly until day 21 of storage, reaching final values of 1.1 (non‐irradiated), 2.0 (1 kGy) and 2.2 mg malonaldehyde kg^?1 muscle (3 kGy), respectively (day 42). Sensory evaluation showed a good correlation with bacterial populations. On the basis of overall acceptability scores (sensory evaluation) a shelf‐life of 28 days (3 kGy) was obtained for vacuum‐packaged sea bream, compared with a shelf‐life of 9–10 days for the non‐irradiated sample. Copyright © 2004 Society of Chemical Industry     

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.     

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.     

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 y‐radiation on chives safety and quality

The effect of γ‐irradiation on the quality of chives was evaluated. The samples were irradiated at 1.0 and 2.0 kGy, stored at 4 °C for 10 days and used for microbiological (aerobic mesophilic, moulds and yeasts, E. coli and Salmonella sp), biochemical (vitamin C and lipoperoxide (MDA) contents and superoxide dismutase (SOD) and guaiacol peroxidase (POX) activity) and sensorial evaluation. For irradiated samples, the total counts of aerobic mesophilic and moulds and yeasts showed a reduction of 6 log cycles during storage, and colour analysis showed no significant difference (P > 0.05) for the b*‐value. The contents of vitamin C were not significantly affected by irradiation and storage time. The MDA contents and SOD activity changed insignificantly at both γ‐irradiation levels after storage, while POX was significantly increased (P ≤ 0.05) at 1 kGy. Samples irradiated at 2.0 kGy presented sensorial acceptance after the storage. These results show that γ‐irradiation increases the shelf life of chives without significant changes in their quality.     

Evaluation of atoxigenic isolates of Aspergillus flavus as potential biocontrol agents for aflatoxin in maize

Aflatoxin contamination resulting from maize infection by Aspergillus flavus is both an economic and a public health concern. Therefore, strategies for controlling aflatoxin contamination in maize are being investigated. The abilities of eleven naturally occurring atoxigenic isolates in Nigeria to reduce aflatoxin contamination in maize were evaluated in grain competition experiments and in field studies during the 2005 and 2006 growing seasons. Treatments consisted of inoculation of either grains in vials or ears at mid-silking stage in field plots, with the toxigenic isolate (La3228) or atoxigenic isolate alone and co-inoculation of each atoxigenic isolate and La3328. Aflatoxin B₁?+?B₂ concentrations were significantly (p?<?0.05) lower in the co-inoculation treatments compared with the treatment in which the aflatoxin-producing isolate La3228 was inoculated alone. Relative levels of aflatoxin B₁?+?B₂ reduction ranged from 70.1% to 99.9%. Among the atoxigenics, two isolates from Lafia, La3279 and La3303, were most effective at reducing aflatoxin B₁?+?B₂ concentrations in both laboratory and field trials. These two isolates have potential value as agents for the biocontrol of aflatoxin contamination in maize. Because these isolates are endemic to West Africa, they are both more likely than introduced isolates to be well adapted to West African environments and to meet regulatory concerns over their use throughout that region.     

Use of PCR for Detecting Aspergillus flavus in Maize Treated by Gamma Radiation Process

The aim of this study was to verify the effects of gamma radiation process on the fungal DNA and the application of PCR in the detection of Aspergillus flavus in irradiated maize grains. The samples were inoculated with a toxigenic strain and incubated under controlled conditions of relative humidity, water activity, and temperature for 15 days. After incubation, the samples were treated with gamma radiation with doses of 5 and 10 kGy and individually analyzed. The use of PCR technique showed the presence of DNA bands of Aspergillus flavus in all irradiated samples that showed no fungal growth in agar medium.     

Reduction in flatulence factors in mung beans (Vigna radiata) using low‐dose γ‐irradiation

Mungbeans (Vigna radiata), control and γ‐irradiated at insect disinfestation dose levels (0.25 and 0.75 kGy) were germinated (0–6 days) and the qualitative and quantitative changes in soluble carbohydrates were studied in detail. The key flatulence‐producing raffinose family oligosaccharides in mungbeans were degraded in the irradiated samples at the onset of the germination (0–2 days) compared to the control where it occurred much later (>4 days). However, the reducing sugars, mainly glucose, fructose and galactose, which are metabolised easily, were enhanced in the irradiated samples. At low dose (0.25 kGy), irradiation had no effect on germination and sprout length, indicating that irradiated beans are suitable for use as sprouted beans. These observations clearly indicate that γ‐irradiation at insect disinfestation dose levels improved the digestibility and nutritional quality of mung beans by reducing the content of oligosaccharides responsible for intestinal gas production. © 1999 Society of Chemical Industry     

CONTAMINATION OF GRAINS BY MYCOTOXIN-PRODUCING MOLDS AND MYCOTOXINS AND CONTROL BY GAMMA IRRADIATION

Ninety random grain samples were collected and analyzed for mycotoxins, and the effect of gamma irradiation on the production of mycotoxins in grains was studied. Aspergillus, Penicillium, Mucor, Rhizopus, Fusarium, Alternaria, Scopulariopsis and Cladosporium were the most common fungal genera isolated from grains. Aspergillus flavus, Aspergillus niger, Aspergillus candidus, Aspergillus ochraceus, Penicillium citrinum, Penicillium expansum, Penicillium citreonigrum, Penicillium purpurogenum, Penicillium griseofulvum and Penicillium verrucosumwere the most common Aspergillus and Penicillium species in grains. Out of 120 Aspergillus and Penicillium isolates, 80 were mycotoxin producers. Analysis of grains revealed the occurrence of aflatoxin B₁ ochratoxin A, cycolopiazonic acid and citrinin. Of the 90 samples, 67 were positive for one or more mycotoxin. Irradiation of grains at dose of 2.0 and 4.0 kGy decreased significantly the total fungal counts compared with unirradiated controls. After 100 days of storage at room temperature, the unirradiated grains were contaminated with high concentrations of mycotoxins as compared with irradiated 4.0‐kGy samples. Mycotoxin production in grains decreased with increasing irradiation doses and was not detected at 6.0 kGy over 100 days of storage.     

Changes in enzyme activities and aflatoxin elaboration in sorghum genotypes following Aspergillus parasiticus infestation

Sorghum is a relatively poor substrate for aflatoxin production compared with high‐risk agricultural commodities like maize and groundnut, even though it is susceptible to fungal attack. Fungal infestation of sorghum results in a varied biochemical composition of the deteriorated grain. In this study, six sorghum genotypes (red—AON 486, IS 620; yellow—LPJ, IS 17 779; white—SPV 86, SPV 462) were inoculated with a toxigenic strain of Aspergillus parasiticus (NRRL 2999) in order to evaluate the changes in the activities of various hydrolytic enzymes (α‐ and β‐amylases, protease and lipase) in comparison with those in uninfected grains. Enzyme activities were measured at different times after fungal infestation, and the enzymatic activities were correlated with the aflatoxin production. Alpha‐amylase activity was observed to be greater than β‐amylase activity in all six genotypes under both healthy and infected conditions. The increase in α‐amylase activity during the period of infection was higher in white genotypes than in red sorghum genotypes. Alpha‐amylase activity in all the genotypes increased up to day 6 after fungal infection, but was significantly lower in infected grains than in healthy grains. The variability in the basal enzyme activities among the six sorghum genotypes was quite high compared with the amount of induction of each specific enzyme due to infection and germination. Higher protease activity was observed in the infected grains than in healthy grains. The enzyme activities in high tannin red genotypes were less than those in yellow and white genotypes. The α‐ and β‐amylase activities were positively correlated (r = 0.406 and 0.436; P < 0.05) to aflatoxin production. Inherent lipase activity was highest (on day 0) in AON 486, SPV 462 and SPV 86, as compared with the activity in infected grains. The total aflatoxins produced (quantified by TLC‐fluorodensitometry) were lower in red genotypes than in yellow and white genotypes, suggesting that red genotypes were least susceptible to aflatoxin elaboration among the various genotypes tested. All four aflatoxins, (B₁, B₂, G₁ and G₂) were present in five genotypes (IS 620, LPJ, IS 17 779, SPV 86 and SPV 462) at all the stages of infection, but, aflatoxin could not be detected in the red genotype AON 486 on day 3 after infection. White genotypes SPV 86 and SPV 462) showed maximal aflatoxin (total) production on day 6 after infection. © 2000 Society of Chemical Industry