Ochratoxin A production in relation to ecophysiological factors by Aspergillus section Nigri strains isolated from different substrates in Argentina

Fumonisins: Impact on Agriculture, Food, and Human Health and their Management Strategies

The fumonisins producing fungi, Fusarium spp., are ubiquitous in nature and contaminate several food matrices that pose detrimental health hazards on humans as well as on animals. This has necessitated profound research for the control and management of the toxins to guarantee better health of consumers. This review highlights the chemistry and biosynthesis process of the fumonisins, their occurrence, effect on agriculture and food, along with their associated health issues. In addition, the focus has been put on the detection and management of fumonisins to ensure safe and healthy food. The main focus of the review is to provide insights to the readers regarding their health-associated food consumption and possible outbreaks. Furthermore, the consumers' knowledge and an attempt will ensure food safety and security and the farmers' knowledge for healthy agricultural practices, processing, and management, important to reduce the mycotoxin outbreaks due to fumonisins.

Impact of some environmental factors on growth and ochratoxin A production by Aspergillus niger and Aspergillus welwitschiae

Ochratoxin A (OTA) is a nephrotoxic mycotoxin which may contaminate various foods and feed products worldwide. Aspergillus niger is one of the species responsible for OTA contamination in grapes and derived products. This species has recently been split into A. niger and Aspergillus welwitschiae. Both species can not be distinguished by phenotypic or extrolite profiles and to date there is no ecophysiological information of A. welwitschiae. The aim of this study was to determine the effects of water activity (a_w) (0.90; 0.95 and 0.98-0.99), culture media (Yeast Extract Sucrose Broth (YESB); Synthetic Grape Juice Medium (SGM); White grape juice (WGJ)) and temperature (15 °C, 25 °C and 35 °C) on the growth and OTA production of four strains of A. niger and six strains of A. welwitschiae. The assay was performed in microtiter plates, determining the absorbance at 530 nm and the concentration of OTA at 1, 2, 4 and 10 days. No significant differences were observed in absorbance and OTA values between the two species under study. The highest absorbance values were recorded in YESB, followed by SGM and WGJ. Absorbance values increased with increasing a_w and temperature. The highest OTA values were obtained at 0.98-0.99 a_w and the best culture media for OTA production was YESB, followed by WGJ and SGM. The studied strains of A. niger produced the highest mean OTA level at 25 °C whereas A. welwitschiae strains produced the highest mean OTA concentration at 15 °C, although not differing significantly from concentration produced at 25 °C. To our knowledge, this is the first report on the impact of some environmental factors on growth and OTA production by A. welwitschiae.

Low Doses of Ochratoxin-A Decrease IgY and IgA Production in Broiler Chicks

The mycotoxin, ochratoxin-A (OTA), produced by some fungi, and is a natural contaminant of many foods and animal feeds worldwide. Due to its toxic effects, the recommended maximum daily intake of OTA for poultry feeds is 0.1 mg OTA/kg (ECR2006/575/EC); this dose does not induce changes in hepatic/renal parameters, but decreases thymus size and serum globulin concentrations. Accordingly, in this study, we assessed quantitatively the total circulating IgY and IgA serum levels, in chicks consuming a 0.1 mg OTA/kg diet (limit) and higher doses (0.3–1.1 mg OTA/kg diet) for 14 or 21 days. We also evaluated other immunological parameters (thymus, bursa of Fabricius, and spleen weights and leukocyte profiles) at day 21. Decreased IgY serum levels were observed in all OTA-treated groups (p < 0.05). In the low-dose group, IgA levels were decreased on day 21, but not on day 14. The size of the thymus and the bursa of Fabricius was decreased in all OTA-treated groups (p < 0.05), whereas reduced spleen size and altered leukocyte profiles were detected only in the high-dose group (p < 0.05). We concluded that chronic exposure to OTA, even at the recommended highest dose, affected IgY and IgA production in chicks.

Determination of potentially mycotoxigenic fungi in coffee (Coffea arabica L.) from Nayarit

A total of fourteen roasted coffee samples were collected from different local markets in Nayarit, Mexico. Twenty-two fungi isolates were related to the genera Aspergillus (54.54%) and Penicillium (4.5%). The strains R16 (0.33 μg/kg), 6N (1.16 μg/kg) and 11 (0.36 μg/kg) tested positive for OTA (ochratoxin A) production in PDA, the other fungi samples were not toxigenic. According to the sequence analysis of their ITS1-5.8S-ITS2 rDNA region, fungi OTA producers correspond to A. niger, A. versicolor and Byssochlamys spectabilis. These three strains were able to produce OTA when inoculated in roasted coffee in concentrations ranging from 75 to 90 μg/kg, after 21 days. Different production stages of roasted coffee (crop management, postharvest practices and storage) along with environmental conditions do not ensure mycotoxigenic fungi free products. This is the first report of OTA natural occurrence in roasted coffee from Nayarit.

Assessment of intraspecies variability in fungal growth initiation of Aspergillus flavus and aflatoxin B1 production under static and changing temperature levels using different initial conidial inoculum levels

Intraspecies variability in fungal growth and mycotoxin production has important implications for food safety. Using the Bioscreen C we have examined spectrophotometrically intraspecies variability of A. flavus using 10 isolates under different environments, including temperature shifts, in terms of growth and aflatoxin B₁ (AFB₁) production. Five high and five low AFB₁ producers were examined. The study was conducted at 5 isothermal conditions (from 15 to 37 °C) and 4 dynamic scenarios (between 15 and 30 °C). The experiments were carried out in a semisolid YES medium at 0.92 a_w and two inoculum levels, 10² and 10³ spores/mL. The Time to Detection (TTD) of growth initiation was determined and modelled as a function of temperature through a polynomial equation and the model was used to predict TTD under temperature upshifts conditions using a novel approach. The results obtained in this study have shown that a model can be developed to describe the effect of temperature upshifts on the TTD for all the studied isolates and inoculum levels. Isolate variability increased as the growth conditions became more stressful and with a lower inoculum level. Inoculum level affected the intraspecies variability but not the repeatability of the experiments. In dynamic conditions, isolate responses depended both on the temperature shift and, predominantly, the final temperature level. AFB₁ production was highly variable among the isolates and greatly depended on temperature (optimum temperature at 30-35 °C) and inoculum levels, with often higher production with lower inoculum. This suggests that, from an ecological point of view, the potential isolate variability and interaction with dynamic conditions should be taken into account in developing strategies to control growth and predicting mycotoxin risks by mycotoxigenic fungi.

Probability models for growth and aflatoxin B1 production as affected by intraspecies variability in Aspergillus flavus

The probability of growth and aflatoxin B₁ (AFB₁) production of 20 isolates of Aspergillus flavus were studied using a full factorial design with eight water activity levels (0.84-0.98 a_w) and six temperature levels (15-40 °C). Binary data obtained from growth studies were modelled using linear logistic regression analysis as a function of temperature, water activity and time for each isolate. In parallel, AFB₁ was extracted at different times from newly formed colonies (up to 20 mm in diameter). Although a total of 950 AFB₁ values over time for all conditions studied were recorded, they were not considered to be enough to build probability models over time, and therefore, only models at 30 days were built. The confidence intervals of the regression coefficients of the probability of growth models showed some differences among the 20 growth models. Further, to assess the growth/no growth and AFB₁/no- AFB₁ production boundaries, 0.05 and 0.5 probabilities were plotted at 30 days for all of the isolates. The boundaries for growth and AFB₁ showed that, in general, the conditions for growth were wider than those for AFB₁ production. The probability of growth and AFB₁ production seemed to be less variable among isolates than AFB₁ accumulation. Apart from the AFB₁ production probability models, using growth probability models for AFB₁ probability predictions could be, although conservative, a suitable alternative. Predictive mycology should include a number of isolates to generate data to build predictive models and take into account the genetic diversity of the species and thus make predictions as similar as possible to real fungal food contamination.

Aflatoxins: A Global Concern for Food Safety, Human Health and Their Management

The aflatoxin producing fungi, Aspergillus spp., are widely spread in nature and have severely contaminated food supplies of humans and animals, resulting in health hazards and even death. Therefore, there is great demand for aflatoxins research to develop suitable methods for their quantification, precise detection and control to ensure the safety of consumers' health. Here, the chemistry and biosynthesis process of the mycotoxins is discussed in brief along with their occurrence, and the health hazards to humans and livestock. This review focuses on resources, production, detection and control measures of aflatoxins to ensure food and feed safety. The review is informative for health-conscious consumers and research experts in the fields. Furthermore, providing knowledge on aflatoxins toxicity will help in ensure food safety and meet the future demands of the increasing population by decreasing the incidence of outbreaks due to aflatoxins.

The effect of dipping pretreatment on ochratoxin A accumulation in sultanas and currants

The dipping pretreatment on the occurrence of ochratoxin A (OTA) in sultanas and currants was investigated. Grape samples were divided into two groups before a drying process. One group was dipped with potassium carbonate-ethyl oleate, and the other group was left without treatment (the control). OTA were detected using solid-phase extraction clean-up and a high-performance liquid chromatography fluorescence detector. Results showed that OTA content was below the limit of detection in the fresh grapes of both varieties. OTA were not detected in dried vine fruits before storage. However, a real naturally environmental storage revealed that the dipping pretreated samples were contaminated with OTA earlier and to a greater extent than the control. The OTA concentration in the treated and control samples after one-year storage was 0.22 and 0.19 μg/kg for sultanas and 0.34 and 0.21 μg/kg for currants, respectively. These results indicated that dipping pretreatment might increase the toxin contamination and safety risk.

Effect of post-harvest treatments on the occurrence of ochratoxin A in raw cocoa beans

Cocoa beans are the principal raw material for chocolate manufacture. Moulds have an important place in the change in the quality of cocoa beans due to their role in the production of free fatty acids and mycotoxins, namely ochratoxin A (OTA). This study investigated the impact of the key post-harvest treatments, namely the fermentation and drying methods on OTA contamination of raw cocoa beans. Analytical methods for OTA detection were based on solid-liquid extraction, clean-up using an immunoaffinity column, and identification by reversed-phase HPLC with fluorescence detection. Of a total of 104 randomly selected cocoa samples analysed, 32% had OTA contents above 2 µg kg(-1). Cocoa sourced from pods in a bad state of health had a maximum OTA content of 39.2 µg kg(-1), while that obtained from healthy pods recorded 11.2 µg kg(-1). The production of OTA in cocoa beans increased according to the pod-opening delay and reached 39.2 µg kg(-1) after an opening delay of 7 days after harvest, while 6.1 and 11.2 µg kg(-1) were observed when pods were opened after 0 and 4 days. OTA production also seemed to depend considerably to the cocoa fermentation materials. When using plastic boxes for bean fermentation, the OTA production was enhanced and reached an average OTA content of about 4.9 µg kg(-1), while the raw cocoa treated in banana leaves and wooden boxes recorded 1.6 and 2.2 µg kg(-1) on average respectively. In parallel, the OTA production was not really influenced by either the mixing or the duration of the fermentation or the drying materials.

Growth parameters of Penicillium expansum calculated from mixed inocula as an alternative to account for intraspecies variability

The aim of this work was to compare the radial growth rate (μ) and the lag time (λ) for growth of 25 isolates of Penicillium expansum at 1 and 20 ºC with those of the mixed inoculum of the 25 isolates. Moreover, the evolution of probability of growth through time was also compared for the single strains and mixed inoculum. Working with a mixed inoculum would require less work, time and consumables than if a range of single strains has to be used in order to represent a given species. Suitable predictive models developed for a given species should represent as much as possible the behavior of all strains belonging to this species. The results suggested, on one hand, that the predictions based on growth parameters calculated on the basis of mixed inocula may not accurately predict the behavior of all possible strains but may represent a percentage of them, and the median/mean values of μ and λ obtained by the 25 strains may be substituted by the value obtained with the mixed inoculum. Moreover, the predictions may be biased, in particular, the predictions of λ which may be underestimated (fail-safe). Moreover, the prediction of time for a given probability of growth through a mixed inoculum may not be accurate for all single inocula, but it may represent 92% and 60% of them at 20 and 1 ºC, respectively, and also their overall mean and median values. In conclusion, mixed inoculum could be a good alternative to estimate the mean or median values of high number of isolates, but not to account for those strains with marginal behavior. In particular, estimation of radial growth rate, and time for 0.10 and 0.50 probability of growth using a cocktail inoculum accounted for the estimates of most single isolates tested. For the particular case of probability models, this is an interesting result as for practical applications in the food industry the estimation of t10 or lower probability may be required.

Effect of indigenous mycobiota on ochratoxin A production by Aspergillus carbonarius isolated from soil: ochratoxin in mixed cultures

This study determined the biotic interaction between 30 non-toxigenic indigenous strains of Aspergillus niger aggregate, Aspergillus flavus, Trichoderma spp., Mucor spp., Cladosporium spp., Ulocladium spp., Curvularia spp., Absidia spp., Geotrichum spp. and Acremonium spp., isolated from soil destined for maize crops, with respect to their ability to prevent ochratoxin A (OTA) production by A. carbonarius on "in vitro" assay, on liquid and solid medium. OTA production was completely inhibited when A. carbonarius was inoculated in a interactive mixed culture with all A. niger aggregate strains assayed, a 80 % of Trichoderma spp. strains, a 40 % of Cladosporium spp. strains, Acremonium spp and Geotrichum spp; only one strain of A. flavus tested was able to completely inhibit the mycotoxin accumulation. OTA production increased when A. carbonarius ACS 8 was growing on liquid interactive mixed culture with Mucor spp strains. These results demonstrated that OTA production by Aspergillua carbonarius strain was significantly influenced by the presence of different non-toxigenic fungal strains when growing together on paired cultures.

Constitutive expression of fluorescent protein by Aspergillus var. niger and Aspergillus carbonarius to monitor fungal colonization in maize plants

Aspergillus niger and Aspergillus carbonarius are two species in the Aspergillus section Nigri (black-spored aspergilli) frequently associated with peanut (Arachis hypogea), maize (Zea mays), and other plants as pathogens. These infections are symptomless and as such are major concerns since some black aspergilli produce important mycotoxins, ochratoxins A, and the fumonisins. To facilitate the study of the black aspergilli-maize interactions with maize during the early stages of infections, we developed a method that used the enhanced yellow fluorescent protein (eYFP) and the monomeric red fluorescent protein (mRFP1) to transform A. niger and A. carbonarius, respectively. The results were constitutive expressions of the fluorescent genes that were stable in the cytoplasms of hyphae and conidia under natural environmental conditions. The hyphal in planta distribution in 21-day-old seedlings of maize were similar wild type and transformants of A. niger and A. carbonarius. The in planta studies indicated that both wild type and transformants internally colonized leaf, stem and root tissues of maize seedlings, without any visible disease symptoms. Yellow and red fluorescent strains were capable of invading epidermal cells of maize roots intercellularly within the first 3 days after inoculation, but intracellular hyphal growth was more evident after 7 days of inoculation. We also tested the capacity of fluorescent transformants to produce ochratoxin A and the results with A. carbonarius showed that this transgenic strain produced similar concentrations of this secondary metabolite. This is the first report on the in planta expression of fluorescent proteins that should be useful to study the internal plant colonization patterns of two ochratoxigenic species in the Aspergillus section Nigri.

Hydrolytic enzymes production by Aspergillus section Nigri in presence of butylated hydroxyanisole and propyl paraben on peanut meal extract agar

BACKGROUND

In the last years, food grade antioxidants are used safely as an alternative to traditional fungicides to control fungal growth in several food and agricultural products.

AIMS

In this work, the effect of butylated hydroxyanisole (BHA) and propyl paraben (PP) on two hydrolytic enzyme activity (β-d-glucosidase and α-d-galactosidase) by Aspergillus section Nigri species under different water activity conditions (aW; 0.98, 0.95 and 0.93) and incubation time intervals (24, 48, 72 and 96h) was evaluated on peanut-based medium.

METHODS

The activity of two glycosidases, β-d-glucosidase and α-d-galactosidase, was assayed using as substrates 4-nitrophenyl-β-d-glucopyranosido and 4-nitrophenyl-α-d-galactopyranosido, respectively. The enzyme activity was determined by the increase in optical density at 405nm caused by the liberation of p-nitrophenol by enzymatic hydrolysis of the substrate. Enzyme activity was expressed as micromoles of p-nitrophenol released per minute.

RESULTS

The major inhibition in β-d-glucosidase activity of A. carbonarius and A. niger was found with 20mmoll(-1) of BHA or PP at 0.98 and 0.95 aW, respectively, whereas for α-d-galactosidase activity a significant decrease in enzyme activity with respect to control was observed in A. carbonarius among 5 to 20mmoll(-1) of BHA or PP in all conditions assayed. Regarding A. niger, the highest percentages of enzyme inhibition activity were found with 20mmoll(-1) of BHA or PP at 0.95 aW and 96h.

CONCLUSIONS

The results of this work provide information about the capacity of BHA and PP to inhibit in vitro conditions two of the most important hydrolytic enzymes produced by A. carbonarius and A. niger species.

Modeling kinetics of aflatoxin production by Aspergillus flavus in maize-based medium and maize grain

Predictive mycology has dealt mainly with germination, growth and inactivation of fungi while the issue of mycotoxin production remains relatively unexplored. Very few studies provide biomass dry weight/colony size data along with mycotoxin data for the same sample times, thus the ratio mycotoxin accumulation per fungal biomass dry weight/colony size has rarely been reported. For this reason, the objective of the present study was to model the kinetics of mycotoxin production under the assumption of existing both no-growth-associated and growth-associated production. Aspergillus flavus was chosen as a model mycotoxigenic microorganism, and it was grown in maize agar medium and maize grain at 0.90 and 0.99 aw at 25°C. A significant positive correlation (p<0.05) was observed among the biomass responses (colony radius and biomass dry weight) in agar medium and colony radius in maize at both aw levels assayed. The Luedeking-Piret model was used to model AFB1 production and reasonable percentages of variability were explained. Moreover, AFB1 production was in general slightly better predicted through colony area. As conclusion, aflatoxin production may follow a mixed-growth associated trend, confirming that toxin formation does not present a clear delay in relation to growth under certain conditions.

Control of ochratoxin A production in grapes

Ochratoxin A (OTA) is a mycotoxin commonly present in cereals, grapes, coffee, spices, and cocoa. Even though the main objective of the food and feed chain processors and distributors is to avoid the extended contamination of plant-derived foods and animal feeds with mycotoxins, until now, complete OTA removal from foods and feedstuffs is not feasible. Prevention through pre-harvest management is the best method for controlling mycotoxin contamination. However, in the case that the contamination occurs after this stage, the hazards associated with OTA must be managed through post-harvest strategies. Due to the increasing number of fungal strains resistant to chemical fungicides and the impact of these pesticides on the environment and human health, maximum levels of chemical residues have been regulated in many products. Alternative methods are necessary to substitute or complement treatments with fungicides to control fungi under field or storage conditions. Yeasts are considered one of the most potent biocontrol agents due to their biology and non-toxic properties. Epiphytic yeasts are the major component of the microbial community on the surface of grape berries and they are evolutionarily adapted to this ecological niche. Nowadays, several yeast species included in different genera are considered as potential biocontrol agents to control both, growth of ochratoxigenic Aspergillus species and OTA accumulation.

The effects of different ecophysiological factors on ochratoxin A production

Mycotoxin biosynthesis is affected by peculiar agro-ecosystem dependent conditions. Accordingly, the correlation between mycotoxin contamination and environmental condition change scenarios should be carefully considered. This is because fungal colonization and mycotoxin contamination could critically impair the availability of food products, especially in poor countries. At any time, the agricultural products might become susceptible to fungal contamination and mycotoxin production in uncontrolled storage. From 2000 to 2010, many studies were carried out in the case of the effects of different parameters on ochratoxin A (OTA) production by fungi in order to avoid providing the appropriate conditions for producing OTA. Water activity (a(w)), temperature, type of species and the substrates were introduced as the most important in these articles. This paper reviews the major published articles regarding the different ecophysiological factors influencing on OTA production.

Coffee berry borer (Hypothenemus hampei)—a vector for toxigenic molds and ochratoxin A contamination in coffee beans

Coffee berry borer (CBB, Hypothenemus hampei Ferrari) is a common insect pest in coffee plantations and is a suspected vector of various mycotoxin-producing molds. In the present study, field trials were undertaken consecutively for 3 years to evaluate the impact of CBB on the microbial contamination of Arabica and Robusta coffee bean varieties, with emphasis laid toward ochratoxin A (OTA)-producing fungi. Results revealed higher microbial contamination in CBB-infested beans in both the varieties of coffee with the presence of toxigenic molds (such as Aspergillus niger, Aspergillus ochraceus). The "timely harvested" coffee, which was infested with CBB, was found to possess comparatively lesser OTA levels than those berries left in soil or on coffee plants. Studies carried out on coffee beans collected from nine curing factories indicated the presence of OTA in almost all the CBB-infested coffee beans, irrespective of the variety. Results of the present study provide sufficient baseline information and evidence to understand and correlate the role of CBB with various OTA-producing molds in coffee beans. Understanding the role of CBB might be useful and applicable in the coffee-growing regions of the world, especially in plantations for production of quality coffee.

Ecophysiology of Aspergillus section nigri species potential ochratoxin a producers

After aflatoxins, ochratoxin A (OTA) is the most studied mycotoxin due to the toxicological significance in human and animal diets. OTA presence has been extensively reported worldwide in the last decade in several agricultural products. The main OTA producer in tropical and temperate climates is Aspergillus carbonarius followed by species belonging to A. niger aggregate. Currently, many scientists worldwide have studied the influence of water activity and temperature for growth and biosynthesis of OTA by these species on synthetic media. This article reviews ecophysiological studies of Aspergillus section Nigri strains on synthetic media and natural substrates. The results of these investigations suggest that significant amounts of OTA can be produced in only five days and that the use of different storage practices, such as a(W) and temperature levels below 0.930 and 15 °C, respectively, allow controlling fungal contamination and minimizing the OTA production in several products as peanuts, corn, dried grapes and derived products for human consumption.

Food-grade antioxidants and antimicrobials to control growth and ochratoxin a production by Aspergillus section Nigri on peanut kernels

Each year, a significant portion of the peanuts produced cannot be marketed because of fungal disease at the postharvest stage and mycotoxin contamination. Antioxidants could be used as an alternative to fungicides to control ochratoxigenic fungi in peanuts during storage. This study was carried out to determine the effect of the antioxidant butylated hydroxyanisole (BHA) and the antimicrobial propyl paraben (PP) on the lag phase before growth, growth rate, and ochratoxin A (OTA) production by Aspergillus section Nigri strains in peanut kernels under different conditions of water activity (aw) and temperature. At 20 mM/g BHA, 18 degrees C, and 0.93 aw, complete inhibition of growth occurred. For PP, there was no growth at 20 mM/g, 18 degrees C, and 0.93, 0.95, and 0.98 aw. BHA at 20 mM/g inhibited OTA production in peanuts by Aspergillus carbonarius and Aspergillus niger aggregate strains at 0.93 aw and 18 degrees C. PP at 20 mM/g completely inhibited OTA production at 18 degrees C. The results of this work suggest that PP is more appropriate than BHA for controlling growth and OTA production by Aspergillus section Nigri species in peanut kernels.

Aspergillus carbonarius growth and ochratoxin A production on irradiated dried grapes under different water activity and temperature conditions

Grapes have different destinations. The most important in the national and international market is wine production, but another is dehydration to produce raisins. Dried vine fruits are at greater risk of ochratoxin A (OTA) contamination than wine grapes because the ratio of Aspergillus carbonarius to Aspergillus niger aggregate increases during drying. The growth of these species, and consequently OTA production, can be influenced by different environmental factors, the two most important being water activity (aW) and temperature. The objective of the present work was to evaluate the lag phase, growth rate and OTA production by two A. carbonarius isolates on irradiated dried grapes at different aW (0.910, 0.928, 0.955, 0.973 and 0.995), temperatures (15, 25 and 30 °C) and incubation times (7, 14 and 21 days). Growth was observed at all aW and temperature ranges assayed. No significant differences between the growth rates reached at 25 °C and 30 °C by both isolates were observed. At the assayed conditions, OTA production occurred over the whole range of temperatures (15-30 °C), with the maximum at 25 and 30 °C depending on the aW. In general, OTA concentration increased as aW increased with no statistically significant differences at the tested incubation times. This work provides information that can be used by companies for the purpose of preventing A. carbonarius and OTA contamination during storage on this and other substrates (e.g. dried prunes, figs and apricots) destined for human consumption.

Ochratoxin A production by a mixed inoculum of Aspergillus carbonarius at different conditions of water activity and temperature

Growth rate, lag phase and OTA production of a mixed inoculum of four Aspergillus carbonarius strains were compared to the behaviour of the single strains at 30 degrees C on Czapek Yeast Extract Agar. Significant differences between radial growth rates and lag phases of the different isolates were observed; however, no significant differences between growth rates of each strain and the mixed inoculum were detected. When the four strains were inoculated simultaneously, the lag phase was the same than the higher value obtained for individual strains, suggesting mycelial interactions between the A. carbonarius isolates. The four strains differed in maximum OTA yield, and the toxin accumulation by the mixed inoculum showed intermediate levels at each time point. The effects of water activity (0.83, 0.85, 0.87, 0.89, 0.90, 0.93 and 0.95) and temperature (15, 20, 25, 30, and 35 degrees C) on OTA production by the mixed inoculum were studied at 7, 14, 21 and 28days of incubation. The limiting water activity for OTA production by the mixed inoculum was 0.87, showing xerotolerant behaviour of the strains isolated from dried vine fruits. Results obtained were similar to those reported for single A. carbonarius strains from European countries, Israel, Australia and South America. The similar trend in the response of the different isolates to the variation of environmental parameters may be of interest for the building of predictive models.

Growth and ochratoxin A production by Aspergillus niger group strains in coffee beans in relation to environmental factors

The effect of water activity (aW), temperature and their interactions on lag phase, mycelial growth rate and ochratoxin A (OTA) production at 7, 14 and 21 days of incubation of two OTA-producer strains belonging to Aspergillus niger group on irradiated coffee beans was determined. Irradiated coffee beans were re-hydrated to 0.910-0.995 of aW with sterile distilled water. The temperatures assayed were 15, 25 and 30 °C. Growth assessment was measured every day during the incubation period to calculate the growth rate. OTA production was examined at 7, 14 and 21 days by high-performance liquid chromatography. Optimal aW for growth was 0.995 at 25 °C for RCC4 and RCC20 strains, being 1.10 and 2.36 mm/day, respectively. OTA concentration varied considerably depending on aW, temperature and incubation time assayed. Maximum OTA production was obtained at 0.973 and 0.995 aW at 30 °C for both strains. The results of the present work indicate that knowledge of the optimal and marginal conditions of black Aspergillus growth and OTA production allow methods to be established for preventing the development of these fungal and mycotoxin production on coffee beans. The data obtained provide useful information for predicting the risk factors for OTA contamination on coffee beans.

OTA-producing fungi isolated from stored cocoa beans

AIMS

The aim of this study was to identify fungal populations in unroasted cocoa beans stored in Spain in order to evaluate the ochratoxin A (OTA)-production ability of certain Aspergillus isolates.

METHODS AND RESULTS

Twenty batches of cocoa beans from different origins and with different OTA content were selected for this study. Three Aspergillus carbonarius and 13 Aspergillus niger aggregate strains isolated from these cocoa bean samples were selected to evaluate their OTA synthesis ability, being the only A. carbonarius isolates which are OTA producers [<limit of detection (LOD) = 3520 microg kg(-1) culture medium; LOD = 6 microg kg(-1) culture medium].

CONCLUSIONS

No correspondence was found between the OTA levels in cocoa beans and the presence of OTA-producing fungi. Nonetheless, some samples contained A. carbonarius with a high OTA-producing ability and, consequently, specific fungal controls should be set up during storage to avoid this toxin.

SIGNIFICANCE AND IMPACT OF THE STUDY

Toxigenic fungi in cocoa beans are not well understood. This study attempted to identify these fungi and evaluate their OTA-producing ability.