Mathematical models to predict kinetic behavior and aflatoxin production of Aspergillus flavus under various temperature and water activity conditions

Mathematical models were developed to predict fungal growth and aflatoxin production of Aspergillus flavus. Fungal growth and aflatoxin concentrations were measured. The Baranyi model was fitted to fungal growth and toxin production data to calculate kinetic parameters. Quadratic polynomial and Gaussian models were then fitted to μ_max and LPD (lag phase duration) values. The ranges of temperature and a _w values showing a μ_max value increase were 15–35°C and 0.891–0.984, respectively. LPD was only observed when the temperature was 20–35°C with a _w=0.891?0.972. The μ_{max growth} value increased up to 35°C with \(b_w = 0.2\left( {b_w = \sqrt {1 - a_w } } \right)\) , then values declined. LPD_growth values increased as the b _w value increased. The μ_max value for aflatoxins increased up to 25°C, but decreased after 30°C, indicating that the developed models are useful for describing the kinetic behavior of Aspergillus flavus growth and aflatoxin production.     

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.     

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.     

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.     

Temperature,water activity and gas composition effects on the growth and aflatoxin production by Aspergillus flavus on paddy

The main aim of this study was to evaluate the combined effects of temperature with water activity (a_w) and CO₂ with a_w on the growth and aflatoxin production by Aspergillus flavus Link on paddy. The effects of temperature (20–30 °C) and a_w (0.92–0.98) on the relationship between colony diameter and aflatoxin production, and the influence of a_w (0.92–0.98) and CO₂ (20–80%) on the growth and toxin production were studied using full factorial design. Colony diameters were regularly measured and aflatoxins were periodically analyzed using HPLC with fluorescence detector. The growth and aflatoxin formation increased with a_w at the temperatures studied, and toxin production was positively correlated with the incubation time and colony diameter. Except at 0.92 a_w, as much as 80% CO₂ failed to inhibit the growth of fungi completely. However, at all a_w levels studied the growth parameters as estimated by Baranyi function and aflatoxin were affected by the increment in CO₂ where growth rates and aflatoxin were negatively correlated with CO₂ while the lag phase durations were positively correlated with CO₂. Under 0.98 a_w, the atmosphere enriched with 20% and 80% CO₂ lead to at least 59% and 88% reduction in growth and 47% and 97% in the toxin production, respectively. At 0.95 a_w, the lag phases of both isolates in average increased by a factor of 1.7–12 when the CO₂ levels in the headspace were between 20 and 80% compared to the control. The growth rate and lag phase durations under the modified atmospheres were successfully described using a polynomial equation (R² > 0.97). The results of the study could form a basis of indicative guidelines on the possible control of A. flavus and aflatoxin in paddy during temporary storage prior to drying.     

Mould contamination and the influence of water activity and temperature on mycotoxin production by two aspergilli in melon seed

Both the moisture levels and the incidence of mould contamination recorded for shelled water melon seed samples (22) obtained from 9 markets were generally higher as those recorded for the unshelled seed samples. 16 fungi, mostly toxigenic, were isolated from the surface-disinfected mouldy seeds. Of these isolates, 7, 3 and 2 species belonged to Aspergillus, Penicillum and Fusarium genera, respectively, while Botryodiplodia, Rhizopus, Sclerotium and Syncephalastrum had one respresentative each. Production of aflatoxins (B₁, B₂) by 5 toxigenic strains of Aspergillus flavus and of ochratoxin A by 4 toxigenic strains of A. ochraceus in melon seed at varying water activity (a_w) and temperature levels were investigated. Of the a_w levels (0.65, 0.70, 0.80, 0.90 and 0.98) provided, toxins were detected only at and above 0.80 with the peak production recorded at either 0.90 or 0.98 a_w level. Whereas aflatoxins were produced and detected under all the test temperatures (15, 20, 25, 30, 35, and 40 °C), the elaboration of ochratoxin A was detected only as from 25 to 40 °C. Optimum temperature for toxin production by all the strains of the two fungi used was 30 °C.     

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 Calcium Propionate and Water Activity on Growth and Aflatoxins Production by Aspergillus flavus

ABSTRACT: The efficacy of calcium propionate at 2 different doses (0.5% and 1%) against growth and aflatoxins production by Aspergillus flavus (A-2092) was investigated in vitro on Czapek yeast extract agar at different levels of water activity (a_w) in the range of 0.94 to 0.996a_w. A. flavus spores germinated on all calcium propionate and a_w treatments; however, 1% calcium propionate at 0.94 a_w delayed the germination process for up to 10 d. The growing rate of mycelia was slower (0.28 mm/d) at 1% calcium propionate and 0.94 a_w. Aflatoxins (B1, B2, G1, and G2) were also produced minimally (36.1, 1, 1.86, and 1.01 ng/g of media, respectively) at the aforementioned dose rate of calcium propionate and water activity. It was concluded that addition of calcium propionate and a_w amelioration can prove effective tools for suppressing the germination, growth rate, and aflatoxins production by A. flavus in substrate.     

Influence of Temperature, pH, Water Activity and Antifungal Agents on Growth of Aspergillus flavus and A. parasiticus

Effect of temperature, pH, water activity, and nine antifungal agents on growth of Aspergillus flavus and A. parasiticus was determined on Sabouraud-Dextrose Agar and on corn. Maximal growth of the two molds occurred at 33°C, the highest temperature used, pH of 5.0 and a_w of 0.99. At 15°C, growth was observed at a_w of 0.95 but not 0.90. Slight growth was observed at an a_w, of 0.85 at 27°C and 33°C. Nine antifungal agents (Botran, Orthocide, Poly-ram 80, Topsin-M, Thiram, Imazalil, sodium propionate, sodium sulfite and DDVP) were tested for inhibition of growth. Activity of the antifungals increased as the a_w was decreased. All antifungals showed inhibitory activity, but Imazalil and DDVP were the most effective agents at the lowest concentrations.     

Comparative study of toxigenic potential of Aspergillus flavus and Aspergillus niger isolated from Barley as affected by temperature,water activity and carbon source

The objective of the present work was to evaluate the ability of two mycotoxigenic species Aspergillus flavus and Aspergillus niger, isolated from barley, to produce aflatoxin B1 (AFB1) and ochratoxin A (OTA), respectively, as affected by nutritional and environmental factors. Six carbon sources (D-fructose, D-glucose, D-galactose, lactose, sucrose and starch) and different water activities (0.90, 0.95 and 0.98), temperature (20 and 28 °C) and incubation time (5 and 10 days) were tested. The results showed that optimal conditions for growth on Barley Meal Extract Agar (BMEA) medium were 28 °C and 0.95 a_w for A. niger strain and 28 °C and 0.98 a_w for A. flavus strain. Optimal conditions for OTA and AFB1 production were largely different for the two tested strains. A. niger had an optimal OTA production at 0.98 a_w and 20 °C after 10 days of incubation while A. flavus had an optimal AFB1 production at 0.95–0.98 a_w and 28 °C after 5 days of incubation. These results indicates that A. flavus has a higher optimum temperature for mycotoxin synthesis than A. niger and takes greater advantage of drier conditions for maximum AFB1 production. In the current study, both OTA and AFB1 production of A. niger and A. flavus were highly influenced by carbon sources. The sugar that provided the highest toxin levels in the cultures of the two species was sucrose with the lowest levels given by starch. OTA production by A. niger was also highly induced by fructose as carbon sources, while, AFB1 production by A. flavus was favored by glucose. Globally, our results showed, significantly different optimal conditions for production of AFB1 and OTA, respectively, by A. flavus and A. niger.     

Moulds and mycotoxins in rice from the Swedish retail market

A survey of moulds and mycotoxins was performed on 99 rice samples taken from the Swedish retail market. The main objective was to study the mould and mycotoxin content in basmati rice and rice with a high content of fibre. Samples of jasmine rice as well as long-grain rice were also included. The samples were analysed for their content of ochratoxin A (high-performance liquid chromatography (HPLC)), aflatoxin B₁, B₂, G₁, and G₂ (HPLC, RIDA®QUICK), and mould (traditional cultivation methods in combination with morphological analysis). The majority of samples were sampled according to European Commission Regulation 401/2006. Subsamples were pooled and mixed before milling and both mould and mycotoxin analyses were performed on milled rice. The results showed that the majority of basmati rice (71%) and many jasmine rice samples (20%) contained detectable levels of aflatoxin B₁ (level of quantification = 0.1 µg aflatoxin kg^?1 rice). Two samples of jasmine rice and ten basmati rice samples contained levels over the regulated European maximum limits of 2 µg kg^?1 for aflatoxin B₁ or 4 µg kg^?1 for total aflatoxins. Aspergillus was the most common mould genus isolated, but also Penicillium, Eurotium, Wallemia, Cladosporium, Epicoccum, Alternaria, and Trichotecium were found. The presence of Aspergillus flavus in 21% of the samples indicates that incorrect management of rice during production and storage implies a risk of mould growth and subsequent production of aflatoxin. Rough estimates showed that high rice consumers may have an intake of 2–3 ng aflatoxin kg^?1 bodyweight and day^?1 from rice alone. This survey shows that aflatoxin is a common contaminant in rice imported to Europe.     

Selected plant essential oils and their main active components,a promising approach to inhibit aflatoxigenic fungi and aflatoxin production in food

Recent research has showed that Aspergillus flavus and Aspergillus parasiticus are aflatoxigenic species that can become very competitive in the framework of climate change. Aflatoxins show carcinogenic, mutagenic, immunotoxic and teratogenic effects on human and animals. Effective and sustainable measures to inhibit these species and aflatoxins in food are required. Origanum vulgare and Cinnamomum zeylanicum essential oils (EOs) and their major active constituents, carvacrol and cinnamaldehyde, respectively, were assayed for inhibiting these species and aflatoxin production in maize extract medium under different environmental conditions. Doses of 10–1000 mg l^?1 were assayed and the effective doses for 50 (ED₅₀) and 90% (ED₉₀) growth inhibition were determined. The ED₅₀ of cinnamaldehyde, carvacrol, oregano EO, and cinnamon EO against A. flavus were in the ranges 49–52.6, 98–145, 152–505, 295–560 mg l^?1 and against A. parasiticus in the ranges 46–55.5, 101–175, 260–425 and 490–675 mg l^?1, respectively, depending on environmental conditions. In A. flavus treatments ED₉₀ were in the ranges 89.7–90.5, 770–860 and 820–>1000 mg l^?1 for cinnamaldehyde, carvacrol and cinnamon EO, and in A. parasiticus treatments in the ranges 89–91, 855–>1000 and 900–>1000 mg l^?1, respectively. ED₉₀ values for oregano EO against both species were >1000 mg l^?1. Growth rates of both species were higher at 37 than at 25°C and at 0.99 than at 0.96 a_w. Aflatoxin production was higher at 25 than at 37°C. Stimulation of aflatoxin production was observed at low doses except for cinnamaldehyde treatments. The effectiveness of EOs and their main constituents to inhibit fungal growth and aflatoxin production in contact assays was lower than in vapour phase assays using bioactive EVOH-EO films previously reported.     

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.     

Production of aflatoxins in sausage,salami, sucuk and kavurma

Forty nine meat product samples were examined for the fungal genera. Penicillium sp. was detected in 74.8% of samples. No sample contained Aspergillus parasiticus or Aspergillus flavus. Production of aflatoxins in sausage, salami, sucuk and kavurma by A. parasiticus and A. flavus was studied at different temperatures. A. parasiticus and A. flavus produced no aflatoxins on meat products samples at 15°C. Sucuk was a poor substrate for A. parasiticus and A. flavus at 25°C. Sausage, salami and kavurma were favorable substrates for aflatoxin production by A. parasiticus at 25°C.     

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.     

Water availability and calcium propionate affect fungal population and aflatoxins production in broiler finisher feed during storage

The aim of this study was to investigate the effects of calcium propionate, water activity (a_w) and incubation time on the total fungal count and aflatoxins B₁ (AFB₁), B₂ (AFB₂), G₁ (AFG₁) and G₂ (AFG₂) production in the broiler finisher feed. The feed was added with calcium propionate (5 g kg^–1), adjusted to 0.85, 0.90 and 0.95 a_w and stored for 28 days at 25°C, analysing for mould growth and aflatoxins production every 7 days. Analysis of variance indicated that all the factors (preservative, a_w and storage time) alone and in combination significantly (p < 0.001) affected the total fungal count and aflatoxins production in the feed. Minimum total fungal counts (1.99 × 10² CFU g^–1) were observed in calcium propionate feed at 0.85 a_w on day 1 and the highest (4.36 × 10⁹ CFUs g^–1) in control sample at 0.95 a_w on day 28 of storage. During the storage period, AFB₁ content in control samples increased from 11.35 to 73.44, from 11.58 to 81.81 and from 11.54 to 102.68 ng g^–1, whereas in preserved feed the content of B₁ increased from 11.47 to 37.83, from 11.54 to 49.07 and from 11.20 to 53.14 ng g^–1 at 0.85, 0.90 and 0.95 a_w, respectively. Similar patterns were noted for AFB₂, AFG₁ and AFG₂ contents. All the aflatoxins readily increased over storage time; however, the increase was much slower in preserved feed that contained a lower amount of available water. This study reveals that calcium propionate addition to poultry litter along with water activity amelioration is an effective tool for controlling mould incidence and aflatoxin production in poultry feed.     

Influence of water activity and temperature on conidial germination and mycelial growth of ochratoxigenic isolates of Aspergillus ochraceus on grape juice synthetic medium. Predictive models

The first stages in the development of Aspergillus ochraceus, an ochratoxin A‐producing fungus that infects grapes and may grow on them, have been studied on a synthetic nutrient medium similar to grape in composition. Spore germination and mycelial growth have been tested over a water activity (a_w) and temperature range which could approximate to the real conditions of fungal development on grapes. Optimal germination and growth were observed at 30 °C for all three isolates tested. Maximal germination rates were detected at 0.96–0.99 a_w at 20 °C, while at 10 and 30 °C the germination rates were significantly higher at 0.99 a_w. Although this abiotic factor (a_w) had no significant influence on mycelial growth, growth rates obtained at 0.98 a_w were slight higher than those at other a_w levels. Predictive models for the lag phase before spore germination as a function of water activity and temperature have been obtained by polynomial multiple linear regression, and the resulting response surface models have been plotted. Copyright © 2005 Society of Chemical Industry     

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.     

Effects of oilseed substrates (ground nyjer and flax seeds) on the growth and Ochratoxin A production by Aspergillus carbonarius

Aspergillus carbonarius is one of the major Ochratoxin A (OTA) producing fungus. Nyjer and flax seeds are important oilseeds that are used for both human and animal consumption, but they are highly susceptible to fungal growth and mycotoxin contamination. The objectives of this study were to determine the growth and OTA production by A. carbonarius on ground nyjer and flax seeds with water activity levels ranging from 0.82 to 0.98 a_w at three incubation temperatures (20, 30, 37°C). It was found that A. carbonarius was not able to grow on the two types of oilseeds with 0.82 or 0.86 a_w. Also, the fungus was not able to grow on flax seeds with high water activity (0.98 a_w). The OTA was only detected on flax seed samples with 0.94 a_w at 20°C. On nyjer seeds, the highest concentration of OTA (271 μg/kg) was detected from samples with 0.98 a_w incubated at 20°C for 5 days, while on flax seeds the highest OTA (146 μg/kg) was found on the seed samples with 0.94 a_w incubated at 20°C for 15 days. Linear regression models also indicated that 0.98 a_w was optimal for both fungal growth and OTA production on nyjer seeds. Overall, ground nyjer seed is better than flax seed to support growth and OTA production by A. carbonarius.     

Relationship between environmental factors,dry matter loss and mycotoxin levels in stored wheat and maize infected with Fusarium species

This study examined the relationship between storage environmental factors (water activity (a _w) (0.89–0.97) and temperature (15°C–30°C)), colonisation of wheat and maize by Fusarium graminearum and F. verticillioides respectively and the dry matter losses (DMLs) caused and quantified by contamination with deoxynivalenol (DON), zearalenone (ZEA) and fumonisins (FUMs) during storage. Fungal growth was assessed by the amount of CO₂ produced under different interacting conditions of a _w and temperature. DMLs were quantified using the cumulative CO₂ data, and these were shown to increase as temperature and a _w increased. The amount of DON, ZEA (wheat for human consumption) and FUMs (feed maize) produced was significantly affected by the storage conditions. The three toxins however showed different patterns of production. Optimum for DON was at the wettest conditions (0.97a _w) and the highest temperature assessed (30°C), whereas for ZEA this shifted to 25°C. FUMs were produced in higher amounts in maize at 30°C and 0.97a _w; however, at intermediate a _w levels (0.955a _w), the highest production occurred at 25°C followed by 20°C. Polynomial models were developed for the effect of the storage factors on DMLs and toxin production. DMLs under different environmental conditions were significantly correlated with DON and FUMs. DON contamination was above the EU limits in at least 80% of the wheat samples with DMLs >1%, whereas at least 70% of the same samples contained ZEA above the respective EU legislative limits. Similarly, at least 75% of the maize samples with DMLs?≥?0.9% exceeded the EU limits for the sum of FUMs in feed. These results show that it may be possible to use temporal CO₂ production during storage of grains as an indicator of the level of contamination of the grain with mycotoxins.