Environmental factors related to fungal infection and fumonisin accumulation during the development and drying of white maize kernels

In Southern Europe where whole maize kernels are ground and used for making bread and other food products, infection of the kernels by Fusarium verticillioides and subsequent fumonisin contamination pose a serious safety issue. The influence of environmental factors on this fungal infection and mycotoxin accumulation as the kernel develops has not been fully determined, especially in such food grade maize. The objectives of the present study were to determine which environmental factors may contribute to kernel invasion by F. verticillioides and fumonisin accumulation as kernels develop and dry in naturally infected white maize. Three maize hybrids were planted at two different sowing dates and kernel samples were collected 20, 40, 60, 80 and 100 days after silking. The percentage of kernels infected, and ergosterol and fumonisin contents were recorded for each sampling. F. verticillioides was the most prevalent species identified as the kernels developed. Temperature and moisture conditions during the first 80 days after silking favored natural kernel infection by F. verticillioides rather than by Aspergillus or Penicillium species. Fumonisin was found in kernels as early as 20 days after silking however significant fumonisin accumulation above levels acceptable in the EU did not occur until after physiological maturity of the kernel indicating that kernel drying in the field poses a high risk. Our results suggest that this could be due to increasing kernel damage by insects that favor fungal development, such as the damage by the moth Sitotroga cerealella, and to the occurrence of stress conditions for F. verticillioides growth that could trigger fumonisin biosynthesis, such as exposure to suboptimal temperatures for growth simultaneously with low water activity.

Impact of cycling temperatures on Fusarium verticillioides and Fusarium graminearum growth and mycotoxins production in soybean

BACKGROUND

Fusarium graminearum and F. verticillioides are two very important mycotoxigenic species as they cause diverse diseases in crops. The effects of constant and cycling temperatures on growth and mycotoxin production of these species were studied on soybean based medium and on irradiated soya beans.

RESULTS

F. graminearum grew better when was incubated at 15, 20 and 15-20 °C (isothermal or cycling temperature) during 21 days of incubation. Maximum levels of zearalenone and deoxynivalenol (39.25 and 1040.4 µg g(-1), respectively) were detected on soya beans after 15 days of incubation and the optimal temperature for mycotoxin production was 15 °C for zearalenone and 20 °C for deoxynivalenol. F. verticillioides grew better at 25 °C in culture medium and at 15/20 °C and 15/25 °C on soybean seeds. Fumonisin B(1) was produced only in culture medium, and the maximum level (7.38 µg g(-1)) was found at 15 °C after 7 days of incubation.

CONCLUSION

When growth and mycotoxin production under cycling temperatures were predicted from the results under constant conditions, observed values were different from calculated for both species and substrate medium. Therefore, care should be taken if data at constant temperature conditions are to be extrapolated to real field conditions.

Ochratoxigenic moulds and effectiveness of grape field antifungals in a climatic change scenario

BACKGROUND

The presence of ochratoxin A (OTA) in grapes and grape derivatives has been reported mainly in the Mediterranean area. Consequently, great efforts are being made to prevent the growth of Aspergillus on grapes. However, the European Commission suggests that climate change may result in increased temperatures and longer drought periods in southern Europe. Therefore the aim of this study was to investigate how ochratoxigenic fungal growth and the efficiency of fungicides used at present might be affected by environmental conditions predicted with climate change.

RESULTS

The effectiveness of grape field antifungals (Switch, Flint Max and Equisetum arvense extract) under two alternating temperature, photoperiod and relative humidity (RH) scenarios (current: 20/30 °C, 16 h light/8 h darkness, 80% RH; predicted: 25/37 °C, 16 h light/8 h darkness, 75% RH) on the growth and OTA production of two Aspergillus carbonarius isolates and one Aspergillus ochraceus isolate on grapes was investigated.

CONCLUSION

Predicted conditions reduced A. carbonarius and limited A. ochraceus growth. Antifungals reduced fungal infection (by 40-84%), although no correlation between climatic conditions and effectiveness of the antifungals was found. However, Switch always showed the greatest reduction and E. arvense (0.02 g mL(-1) extract) the least. Higher temperatures affected OTA production by the isolates in different ways. In general, Switch and Flint Max reduced OTA production, while E. arvense stimulated it.

Modelling the effect of temperature and water activity of Aspergillus flavus isolates from corn

The aim of this study was to model the effects of temperature (10-40 °C) and a(w) (0.80-0.98), in two media (Czapek yeast agar: CYA; corn extract medium: CEM) on the growth rates and growth boundaries (growth-no growth interface) of three strains of A. flavus isolated from corn in Argentina. Both kinetic and probability models were applied to colony growth data. The growth rates obtained in CYA were significantly (p<0.05) greater than those obtained in CEM medium. No significant differences (p<0.05) were observed among the three isolates. The growth rate data showed a good fit to the Rosso cardinal models combined with the gamma-concept with R(2)=0.98-0.99 and RMSE=0.60-0.78, depending on media and isolates. The probability model allowed prediction of safe storage (p of growth <0.01) for one month for moist maize (e.g. 0.90 a(w)) provided temperature is under 15 °C, or for dry maize (e.g. 0.80 a(w)) provided temperature is under 27 °C. Storage at <0.77 a(w) would be safe regardless of the storage temperature. Probability models allow evaluation of the risk of fungal contamination in the process of storage, so the results obtained in this study may be useful for application in systems of food safety management.

In vitro effect of some fungicides on growth and aflatoxins production by Aspergillus flavus isolated from Capsicum powder

The aim of this study was to determine the effect of some pre-harvest fungicides on growth and aflatoxin (AF) production of three Aspergillus flavus strains found in Capsicum powder. Each isolate, previously isolated from paprika, chilli and smoked paprika, was inoculated on yeast extract sucrose agar and on a 3% paprika extract agar medium supplemented with different fungicides and incubated at 20 and 30°C during 7 days. Growth measurements were obtained on days 3, 5 and 7, and the AF production was determined on day 7. The significance of the effects of the factors (strain, medium, temperature, time and fungicides) and their interaction over colony diameter and AF production was determined. Temperature constrained the effectiveness of fungicides in reducing growth, the fungicides being most effective at 20°C. The efficacy of the fungicides over AF production depended on the medium used and temperature. The most effective fungicides in inhibiting growth and AF production, regardless of the strain tested or applied conditions, were tebuconazole 25% and mancozeb 80% applied at a concentration of 0.75 and 3.5 g l(-1), respectively. Care should thus be taken in the choice of a suitable fungicide because their effectiveness may depend on intra-specific variation and temperature. Moreover, it is necessary to take into account that the most efficient fungicide in reducing growth is not always the best choice for pre-harvest treatments because it may promote AF production. Thus, the best fungicide is the one that can simultaneous prevent growth and AF production.

Effect of Capsicum carotenoids on growth and ochratoxin A production by chilli and paprika Aspergillus spp. isolates

The aim of this study was to determine the effect of a natural carotenoid mixture (Capsantal FS-30-NT), containing capsanthin and capsorubin, on growth and mycotoxin production of ochratoxin A-producing A. ochraceus, A. westerdijkiae, and A. tubingensis isolates. One isolate of each species, previously isolated from paprika or chilli, was inoculated on Czapek Yeast extract Agar (CYA) medium supplemented with different amounts of capsantal (0 to 1%) and incubated at 10, 15 and 25 degrees C for 21days. Growth rates and lag phases were obtained, and OTA production was determined at 7, 14 and 21days. The taxonomically related A. ochraceus and A. westerdijkiae showed the same behavior at 15 degrees C, but A. ochraceus was able to grow at 10 degrees C and had higher growth rates at 25 degrees C. A. tubingensis had the highest growth rates and lowest OTA production capacity of the assayed isolates, and it was not able to grow at 10 degrees C. Capsantal addition resulted in increased lag phases at 15 degrees C for all the strains, while growth rates remained rather constant. At 25 degrees C capsantal reduced growth rates, with rather constant lag phases. However, the effect of capsantal on OTA production was inconclusive, because it depended on temperature or time, and mostly was not significant. Low temperature has been a crucial factor in OTA production, regardless of the capsantal concentration tested, especially for A. tubingensis and A. westerdijkiae. Industrial storage temperature for paprika and chilli is approximately 10 degrees C. If this temperature is maintained, mould growth and OTA production should be reduced.

Occurrence of aflatoxin M₁ and exposure assessment in Catalonia (Spain)

BACKGROUND

Aflatoxin M₁ (AFM₁) is the main monohydroxylated derivative of aflatoxin B₁ (AFB₁) formed in liver and excreted into milk. Although AFM₁ is less toxic than AFB₁, it has been classified as a possible human carcinogen, Group 2B agent by International Agency for Research on Cancer (IARC).

OBJECTIVES

The objectives of this study were (i) to determine the occurrence of AFM₁ in the main dairy products consumed in Catalonia region (Spain), and (ii) to assess the exposure of Catalonian population to aflatoxin M₁ through deterministic and probabilistic method.

METHODS

Occurrence of Aflatoxin M₁ (AFM₁) was determined in 72 composites of milk, 72 composites of cheese and 72 composites of yoghurt from Catalonia. AFM₁ content was analysed using an Enzyme-Linked ImmunoSorbent Assay commercial kit. Three approaches to exposure assessment were conducted: one deterministic method and two probabilistic models with Monte Carlo simulations.

RESULTS

AFM₁ was detected in 94.4% (68/72) of whole UHT milk samples, in 2.8% (2/72) of yoghurt samples and not detected in cheese. The maximum level was detected in one yoghurt sample with 51.58 ng/kg, only this sample being over the legal EU limit of 50 ng/kg. Milk, cheese and yoghurt mean concentrations were 9.29±2.61, <12.5 and 13.22±4.82 ng/kg, respectively.

CONCLUSIONS

According to these values, it should be expected Catalonian population is not exposed to a significant risk from aflatoxin M₁ including average and high consumers.

Brief in vitro study on Botrytis cinerea and Aspergillus carbonarius regarding growth and ochratoxin A

AIMS

To evaluate the effect of Botrytis cinerea growth on ochratoxin A (OTA) production by Aspergillus carbonarius and degradation.

METHODS AND RESULTS

OTA-producing A. carbonarius and B. cinerea were grown on grape-like medium at 20 degrees C for 7 days. Radii of colonies were daily recorded and OTA was analysed. In addition, each B. cinerea isolate was inoculated on grape-like synthetic nutrient medium (SNM) paired with each A. carbonarius isolate at a distance of 45 mm. Botrytis cinerea isolates were also grown in OTA-spiked SNM. Growth rates of B. cinerea and A. carbonarius were 20 and 75 mm day(-1), respectively. The growth of the colonies of each species stopped when they contacted each other in paired cultures. OTA production by A. carbonarius in the contact area was affected by B. cinerea, but no clear trend was observed. All B. cinerea isolates showed to degrade between 24.2% and 267% of OTA from spiked SNM.

CONCLUSIONS

The ecological advantage of B. cinerea, in terms of growth rate, vs. OTA-producing Aspergillus in some wine-growing regions and its ability to degrade OTA may explain the low levels of this toxin in noble wines.

SIGNIFICANCE AND IMPACT OF THE STUDY

At determinate conditions, the presence of B. cinerea in grapes with A. carbonarius may help in reducing OTA accumulation.

Modelling of growth of aflatoxigenic A. flavus isolates from red chilli powder as a function of water availability

The aim of the present work was to apply mathematical models for the prediction of growth of aflatoxigenic moulds in powdered Capsicum fruits as a function of its water availability. As prevention of fungal growth effectively conduces to prevention of mycotoxin accumulation, the development of models for prediction of growth of mycotoxigenic fungi becomes a key step in risk management. Two aflatoxigenic A. flavus from chilli powder were grown on 3% chilli powder extract agar at different water activity levels and their growth was evaluated over time in terms of colony sizes and ergosterol accumulation. Both variables were modelled over time, and the resulting parameters (growth rates and lag phases) were modelled as a function of water availability using the Rosso cardinal model. Linear logistic regression was also applied to predict the probability of growth over storage time. Both isolates showed a similar pattern of behaviour, with decreasing growth rates and increasing lag phases with decreasing water activity level. While estimation of optimum a(w) for growth was consistently around 0.97-0.99, the minimum estimated a(w) varied from 0.82 to 0.88 depending on the isolate and on the parameters used for predictions. Comparing growth rates obtained for colony size and ergosterol accumulation, a linear relationship between them could be observed. The rate of root square ergosterol/colony diameter/unit of time was 0.25-0.27. Probabilities of growth before 10 days over 90% were estimated at a(w) 0.91, while the safe period could be extended to more than 20 days (22-29 days) if water activity was decreased to an a(w)=0.87. Finally, the probability of growth is always under 50% when water availability is under a(w) 0.85, and almost null for A. flavus UdLTA 3.147. It was concluded that for safe production, storage and transport, chillies and chilli powder must be kept under 31% mc (db) (probability of growth <50%). However, growth is unlikely to occur if chilli is kept at approx. 34% for less than 10 days, or at approx. 33% for less than 20 days. Careful hazard analysis and critical control point (HACCP) techniques during raw material production and the subsequent stages of drying, transportation, elaboration and storage are indispensable.

Morphological and electrical properties of human trophoblast choriocarcinoma, BeWo cells

The syncytiotrophoblast of the human placenta arises from fusion of stem cells called cytotrophoblasts. The molecular mechanisms associated with cell fusion and syncytiation of cytotrophoblastic cells remain largely unknown. In the present study, we investigated the morphological and electrical properties of BeWo cells, a human choriocarcinoma-derived trophoblast cell model, with several features of the human cytotrophoblast. Cultured cells tended to cluster, but only fused into small, multinucleated syncytia in the presence of cAMP (72 h). The morphological features of both the actin and microtubular cytoskeletons indicated that within 72 h of constant exposure to cAMP, intracellular cortical actin cytoskeleton disappeared, which was the most prominent inducing factor of multi-nucleation. The presence of the cation channel protein, polycystin-2 (PC2), a TRP-type cation channel, associated with placental ion transport in term human syncytiotrophoblast, co-localised with acetylated tubulin in midbodies, but was found non-functional under any conditions. Different electrical phenotypes were observed among control BeWo cells, where only 26% (8 of 31 cells) displayed a voltage-dependent outwardly rectifying conductance. Most quiescent BeWo cells had, however, a low, slightly outwardly rectifying basal whole cell conductance. Acute exposure to intracellular cAMP (<15 min) increased the whole cell conductance by 122%, from 0.72 nS/cell to 1.60 nS/cell, and eliminated the voltage-regulated conductance. The encompassed evidence indicates that the early events in BeWo cell fusion and syncytiation occur by cAMP-associated changes in ionic conductance but not morphological changes associated to chronic exposure to the second messenger. This suggests a tight regulation, and important contribution of cation conductances in cytotrophoblastic cells prior to syncytiation.

Co-inheritance of a PKD1 mutation and homozygous PKD2 variant: a potential modifier in autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD), which is caused by mutations in polycystins 1 (PC1) and 2 (PC2), is one of the most commonly inherited renal diseases, affecting ~1 : 1000 Caucasians.

MATERIALS AND METHODS

We screened Greek ADPKD patients with the denaturing gradient gel electrophoresis (DGGE) assay and direct sequencing.

RESULTS

We identified a patient homozygous for a nucleotide change c.1445T > G, resulting in a novel homozygous substitution of the non-polar hydrophobic phenylalanine to the polar hydrophilic cysteine in exon 6 at codon 482 (p.F482C) of the PKD2 gene and a de-novo PKD1 splice-site variant IVS21-2delAG. We did not find this PKD2 variant in a screen of 280 chromosomes of healthy subjects, supporting its pathogenicity. The proband's parents did not have the PKD1 mutation. Real-time PCR of the PKD2 transcript from a skin biopsy revealed 20-fold higher expression in the patient than in a healthy subject and was higher in the patient's peripheral blood mononuclear cells (PBMCs) than in those of her heterozygote daughter and a healthy subject. The greater gene expression was also supported by Western blotting. Inner medullar collecting duct (IMCD) cells transfected with the mutant PKD2 mouse gene presented a perinuclear and diffuse cytoplasmic localization compared with the wild type ER localization. Patch-clamping of PBMCs from the p.F482C homozygous and heterozygous subjects revealed lower polycystin-2 channel function than in controls.

CONCLUSIONS

We report for the first time a patient with ADPKD who is heterozygous for a de novo PKD1 variant and homozygous for a novel PKD2 mutation.

Distribution of fumonisins and aflatoxins in corn fractions during industrial cornflake processing

The aim of this study was to investigate the distribution of fumonisins (B(1) B(2,) and B(3)) and total aflatoxins (B(1), B(2), G(1), and G(2)) in various corn processed fractions. 92 batches of whole corn and derived dry-milled fractions (animal feed flour, flaking grits, corn flour and corn meal) and cooked and roasted cornflakes fractions were industrially obtained. Samples were analyzed for both groups of mycotoxins by enzyme-linked immunosorbent assay (ELISA). Dry milling of corn led to a heterogeneous distribution of the two groups of mycotoxins in the different parts of the grain, with increased levels in fractions processed from outer layers (animal feed flour and corn flour) and decreased levels in fractions processed from inner portions, such as corn meal and flaking grits. Levels of fumonisins in cornflakes were lower than 400 microg/kg, the maximum tolerable limit set by the EU. By contrast, three samples of final product were found to exceed the aflatoxin maximum tolerable limit of 4 microg/kg. Animal feed flour showed concentration factors of 317 and 288% for fumonisins and aflatoxins, respectively. Food traceability system was used by the industrial companies which processed corn into breakfast cereals. Nevertheless, even though the use of food traceability, which is defined as the ability to trace any food, feed, food-producing animal or substance that will be used for consumption through all stages of production, processing and distribution, only initial fumonisin contamination of whole corn and contamination of animal feed flour and corn flour were found to be correlated.

Effect of biocontrol agents Candida sake and Pantoea agglomerans on Penicillium expansum growth and patulin accumulation in apples

Penicillium expansum is the major responsible of fruit pome decaying in cold storage. Apples spoiled by P. expansum are expected to contain patulin, a mycotoxin which is proven to affect human health. The use of chemicals is the most common procedure to prevent rots in postharvest but legislation is becoming more and more restrictive. The use of biocontrol agents (BCA) as an alternative tool is currently being proposed. The aim of this study was to evaluate the effect of two BCA (Candida sake CPA-2 and Pantoea agglomerans CPA-1) on P. expansum growth and patulin accumulation in cold storage and further deck (ambient) storage. Wounded apples were inoculated with a cell suspension of either C. sake or P. agglomerans and with a P. expansum conidial suspension. Apples were cold stored at 1 degrees C until lesion diameter reached 2 or 4 cm. Half the apples of each treatment were further stored at 20 degrees C for three days before patulin analyses. Both BCA tested controlled blue rot and patulin accumulation during cold storage. The control of P. expansum growth was enhanced in C. sake treated apples. On the other side, control of patulin accumulation in P. agglomerans treated apples seemed to be more efficient. BCA treatment could not control blue rot and patulin accumulation during further storage at room temperature and in some cases, an increase in P. expansum aggressiveness was observed.