Effect of water activity and temperature on growth and fumonisin B1 and B2 production by Fusarium proliferatum and F. moniliforme on maize grain

Aspergillus flavus and Fusarium verticillioides and Their Main Mycotoxins: Global Distribution and Scenarios of Interactions in Maize

Maize is frequently contaminated with multiple mycotoxins, especially those produced by Aspergillus flavus and Fusarium verticillioides. As mycotoxin contamination is a critical factor that destabilizes global food safety, the current review provides an updated overview of the (co-)occurrence of A. flavus and F. verticillioides and (co-)contamination of aflatoxin B1 (AFB1) and fumonisin B1 (FB1) in maize. Furthermore, it summarizes their interactions in maize. The gathered data predict the (co-)occurrence and virulence of A. flavus and F. verticillioides would increase worldwide, especially in European cold climate countries. Studies on the interaction of both fungi regarding their growth mainly showed antagonistic interactions in vitro or in planta conditions. However, the (co-)contamination of AFB1 and FB1 has risen worldwide in the last decade. Primarily, this co-contamination increased by 32% in Europe (2010-2020 vs. 1992-2009). This implies that fungi and mycotoxins would severely threaten European-grown maize.

Evaluation of the Antimicrobial Activity of Four Plant Essential Oils against Some Food and Phytopathogens Isolated from Processed Meat Products in Egypt

Synthetic preservatives are widely utilized by the food industry to inhibit the microbial contamination and increase food safety and shelf life. The excessive utilization of synthetic preservatives can have a negative impact on human health and the environment. There is a great interest to find out natural substances as possible food-preservatives. The consumers’ preference for food products with natural ingredients prompted food manufacturers to utilize natural-based preservatives in their production. It is worth noting that plant essential oils (EOs) among the natural-based substances have been efficiently used as antimicrobial agents against phyto- and food pathogens. The current study was conducted to evaluate the microbial contamination of three industrial meat products from five governorates in Egypt, identify the predominant bacterial and fungal isolates and determine the antimicrobial efficacy of some EOs (thyme, fennel, anise and marjoram) against the most predominant microbial isolates. A sensory test was also performed to estimate the customer preferences for specific organoleptic aspects of meat products after EOs treatment. Results showed that there is a promising antimicrobial activity of all studied EOs against some microbial isolates in a dose-dependent manner. In particular, thyme EO showed the highest significant antibacterial activity against P. fluorescence and E. coli. Whereas the marjoram EO showed the highest activity against P. aeruginosa. In addition, the sensory test revealed that the treatment with anise and marjoram EOs showed the highest acceptability by the testers and did not show significant differences on the organoleptic properties with respect to control. As overall, the obtained results of the current research are promising and proved feasibility of employing plant EOs as possible preservatives for processed meat products.

Influence of H2O2-Induced Oxidative Stress on In Vitro Growth and Moniliformin and Fumonisins Accumulation by Fusarium proliferatum and Fusarium subglutinans

Fusarium proliferatum and Fusarium subglutinans are common pathogens of maize which are known to produce mycotoxins, including moniliformin (MON) and fumonisins (FBs). Fungal secondary metabolism and response to oxidative stress are interlaced, where hydrogen peroxide (H₂O₂) plays a pivotal role in the modulation of mycotoxin production. The objective of this study is to examine the effect of H₂O₂-induced oxidative stress on fungal growth, as well as MON and FBs production, in different isolates of these fungi. When these isolates were cultured in the presence of 1, 2, 5, and 10 mM H₂O₂, the fungal biomass of F. subglutinans isolates showed a strong sensitivity to increasing oxidative conditions (27–58% reduction), whereas F. proliferatum isolates were not affected or even slightly improved (45% increase). H₂O₂ treatment at the lower concentration of 1 mM caused an almost total disappearance of MON and a strong reduction of FBs content in the two fungal species and isolates tested. The catalase activity, surveyed due to its crucial role as an H₂O₂ scavenger, showed no significant changes at 1 mM H₂O₂ treatment, thus indicating a lack of correlation with MON and FB changes. H₂O₂ treatment was also able to reduce MON and FB content in certified maize material, and the same behavior was observed in the presence and absence of these fungi, highlighting a direct effect of H₂O₂ on the stability of these mycotoxins. Taken together, these data provide insights into the role of H₂O₂ which, when increased under stress conditions, could affect the vegetative response and mycotoxin production (and degradation) of these fungi.

Enantioselective Effect of Flutriafol on Growth, Deoxynivalenol Production, and TRI Gene Transcript Levels in Fusarium graminearum

In recent years, deoxynivalenol (DON) has frequently been detected in wheat grains and their products. The enantioselective impact of flutriafol on the growth and DON biosynthesis of Fusarium graminearum was investigated in relation to water activity (α_w, 0.97 and 0.99) and temperature (20, 25, and 30 °C) on the wheat-based medium. R-(-)-flutriafol exhibited higher bioactivity than S-(+)-flutriafol and Rac-flutriafol under the above conditions. Flutriafol enantiomers reduced or stimulated DON biosynthesis depending on α_w. DON levels were negligible after 14 or 7 days of incubation times under 0.97 and 0.99 a_w, respectively. Quantitative real-time polymerase chain reaction (qRT-PCR) analyses showed that the expression levels of trichothecene biosynthetic (TRI) genes of F. graminearum under 0.97 a_w were significantly higher than those under 0.99 a_w. In addition, R-(-)-flutriafol can induce more TRI gene expression than S-(+)-flutriafol. Taken together, this study indicated that a_w and temperature play important roles in regulating DON biosynthesis in F. graminearum with flutriafol enantiomers.

Distribution of fungi and their toxic metabolites in melon and sesame seeds marketed in two major producing states in Nigeria

In this study, melon (n = 60) and sesame (n = 60) seeds purchased from markets within Benue and Nasarawa states, respectively, in Nigeria, during two seasons (dry and wet), were analysed for fungal and mycotoxin contamination in order to determine the safety of these foods for human consumption. Molecular analysis revealed the following seven fungal taxonomic groups in the foods: Aspergillus section Candidi, Aspergillus section Flavi, Aspergillus section Nigri, Cladosporium, Fusarium fujikuroi species group, Penicillium, and Pleosporales/Didymellaceae. A total of 78 microbial metabolites, including several mycotoxins, occurred in the foods. The most frequent mycotoxins in melon and sesame were aflatoxin B1 (occurrence: 76%) and alternariol monomethyl ether (occurrence: 59%), respectively. However, higher mean total aflatoxin levels occurred in sesame (17 μg kg-1) than in melon (11 μg kg-1). About 28 and 5% of melon and sesame, respectively, exceeded the 4 μg kg-1 total aflatoxin limit for oilseeds intended for direct human consumption in the European Union. Additionally, fumonisin B1 and moniliformin occurred only in sesame, whilst ochratoxins A and B occurred only in melon; ochratoxin B being reported for the first time in this food. Our data indicated seasonal variations in the fungal and mycotoxin contamination levels in both foods.

Aspergillus flavus and Fusarium verticillioides Interaction: Modeling the Impact on Mycotoxin Production

The influence of climate change on agricultural systems has been generally accepted as having a considerable impact on food security and safety. It is believed that the occurrence of mycotoxins will be greatly affected by future climate scenarios and this has been confirmed by recent data. Temperature (T) and CO2 increases, variation in rain intensity and distribution, as well as extreme weather events, affect the dominant fungal species in different ways, depending on their ecological needs. Therefore, the aim of this work was to study Aspergillus flavus (Af) and Fusarium verticillioides (Fv) co-occurrence in vitro in order to collect quantitative data on the effect of fungal interaction on growth and mycotoxin production and develop functions for their description. Experimental trials were organized with the cited fungi grown alone or together. They were incubated at different T regimes (10-40°C, step 5°C) for 21 days. Fungal growth was measured weekly, while AFs and FBs were quantified at the end of the incubation period. Temperature and incubation time significantly affected fungal growth both for Af and Fv (p ≤ 0.01), and a significant interaction between T and the presence of one versus both fungi influenced the amount of AFs and FBs produced. Each fungus was affected by the presence of the other fungus; in particular, Af and Fv showed a decrease in colony diameter of 10 and 44%, respectively, when they were grown together, compared to alone. The same influence was not found for mycotoxin production. In fact, the dynamics of toxin production in different temperature regimes followed a comparable trend with fungi grown alone or together, but a significant impact of inoculum × temperature interaction was highlighted. Fungal growth and toxin production in different T regimes were well described, both for AFs and FBs, by a Bete function. These results are the first attempt to model mycotoxigenic fungal co-occurrence under several T regimes; this is essential in order to improve effective prediction of growth and mycotoxin production by such fungi.

Mycotoxin occurrence in Peruvian purple maize

The presence of mycotoxins in 82 samples of Peruvian purple maize was determined by LC-MS/MS methods. Samples were collected from local commercial establishments in Peru from December 2015 to March 2016, and from March 2017 to April 2017. Aflatoxins (AF) (64.6%) and fumonisins (FB) (63.4%) were the most common mycotoxins, with average values of 2.1 (1-17) and 2,586 (125-27,490) μg/kg, respectively. Zearalenone (ZEA) was identified in a single sample at 24.4 μg/kg. Co-occurrence of AF and FB was confirmed in 45.1% of the samples (n=37), which presented significant (P<0.05) Spearman correlation (ρ=0.59) between these mycotoxins. Co-occurrence of AF, FB and ZEA was found in one sample and ZEA was found in one sample. Ochratoxin A, deoxynivalenol, nivalenol, fusarenone X, diacetoxyscirpenol, 3-acetyldeoxinivalenol, HT-2 toxin and T-2 toxin were not detected. Water activity (Aw) of these samples exceeded 0.73; there was no correlation between Aw and the levels of mycotoxins. This is the first study to evaluate the occurrence of mycotoxins in Peruvian purple maize, and it ascertained that this variety may pose a risk to public health. Therefore, there is a need to control this grain supply chain in order to determine the factors involved in the presence of these toxins, and to establish regulatory limits or guidelines for maximum tolerated levels.

Impact of Fungi Co-occurrence on Mycotoxin Contamination in Maize During the Growing Season

Maize is a possible host of many fungi, some of them able to produce different mycotoxins. Few studies exist on co-occurring fungi and resulting multi-mycotoxin contamination in field; for this reason, in field trials were conducted in two consecutive years to verify fungal incidence and mycotoxin production in the case of the co-occurrence of the three main mycotoxigenic fungi of maize in Italy: Aspergillus flavus, Fusarium verticillioides, and Fusarium graminearum able to produce, respectively, aflatoxin B1 (AFB1), fumonisins (FBs), and deoxynivalenol (DON). Artificial inoculation was done after silk emergence of maize and samples were collected with a 2 week schedule up to harvest time (four samplings). Fungal interaction resulted as playing a role for both fungal incidence and mycotoxins production, as did weather conditions too. Main interactions were noted between A. flavus and F. verticillioides, and between F. verticillioides and F. graminearum. In particular, as a result of fungal co-occurrence, AFB1 resulted stimulated by F. graminearum presence while no effects were noted in FBs and DON in case of F. verticillioides-F. graminearum co-occurrence. Interestingly, the co-presence of A. flavus significantly reduced both FB and DON production.

Assessment of Aflatoxin and Fumonisin Contamination and Associated Risk Factors in Feed and Feed Ingredients in Rwanda

Mycotoxins are fungal metabolites that contaminate crops, food, and animal feeds. Aflatoxins and fumonisins are among the mycotoxins that have been increasingly reported to affect health and productivity of livestock globally. Given that the health and productivity of livestock can directly influence human food safety and security, a study was conducted to assess the levels and factors for aflatoxin and fumonisin contamination in feed and feed ingredients in Rwanda. Aflatoxins and fumonisins were analyzed in 3328 feed and feed ingredient samples collected at six time points between March and October 2017 in all 30 districts of Rwanda. Of the 612 participants providing samples, there were 10 feed processors, 68 feed vendors, 225 dairy farmers, and 309 poultry farmers. Enzyme-Linked Immunosorbent Assay (ELISA) was used for aflatoxin and fumonisin analyses. Mean aflatoxin levels of 108.83 µg/kg (Median (MD): 43.65 µg/kg), 103.81µg/kg (MD: 48.4 µg/kg), 88.64 µg/kg (MD: 30.90 µg/kg), and 94.95 µg/kg (MD: 70.45 µg/kg) were determined for dairy farmers, poultry farmers, feed vendors, and feed processors, respectively. Mean fumonisin levels were 1.52 mg/kg (MD: 0.71 mg/kg), 1.21 mg/kg (MD: 0.56 mg/kg), 1.48 mg/kg (MD: 0.76 mg/kg), and 1.03 mg/kg (MD: 0.47 mg/kg) for dairy farmers, poultry farmers, feed vendors, and feed processors, respectively. Aflatoxin contamination was significantly affected by time of sampling and district from which feed samples originated (p < 0.05). Fumonisins did not show any correlation trends. Ninety-two percent of survey participants were unaware of aflatoxins and fumonisins and their adverse effects. This study has provided the basic understanding of the extent of feed contamination across the country and has established a baseline for future interventions in Rwanda. Further studies are needed to explore strategies for mitigating mycotoxins in the feed value chain in Rwanda.

Mycotoxins produced by Fusarium proliferatum and F. pseudonygamai on maize, sorghum and pearl millet grains in vitro

Maize (Zea mays), sorghum (Sorghum bicolor) and pearl millet (Pennisetum glaucum) are basic staple foods for many rural or poorer communities. These crops are susceptible to plant diseases caused by multiple species of Fusarium, some of which also produce mycotoxins, including fumonisins and moniliformin that are detrimental to both humans and domesticated animals. Eighteen potentially toxigenic Fusarium strains were isolated from maize (n = 10), sorghum (n = 7) and pearl millet (n = 1) growing in the same field in Nigeria. The 17 strains from maize and sorghum were all F. proliferatum and the one strain from pearl millet was F. pseudonygamai. Under conducive conditions, the 17 F. proliferatum strains produced fumonisins, 11 in relatively large quantities (700-17,000 mg total fumonisins, i.e., FB₁ + FB₂ + FB₃/kg culture material), and six at <45 mg/kg. Ten F. proliferatum strains produced >100 mg of moniliformin per kg culture material with a maximum of 8900 mg/kg culture material. All strains could use all grains for growth and toxin production, regardless of the host from which they were isolated. Isolates varied in the amount of toxin produced on each substrate, with toxin production a property of the strain and not the host from which the strain was recovered. However, the extent to which a toxin-producing phenotype could be altered by the grain on which the fungus was grown is consistent with subtle genetic × environment interactions that require a larger data set than the one presented here to rigorously identify. In conclusion, there is significant variation in the ability of strains of F. proliferatum to produce fumonisins and moniliformin on maize, sorghum and millet. If the amount of toxin produced on the various grains in this study reflects real-world settings, e.g., poor storage, then the consumers of these contaminated grains could be exposed to mycotoxin levels that greatly exceed the tolerable daily intakes.

Quality and safety of maize (Zea mays L.) from Rondônia state storage units, Northern Brazil

The quality and safety of maize (Zea mays L.) from different grain storage units (GSUs), located in the main producing region of Rondônia State, Northern Brazil, were evaluated. Maize grains (n = 76) stored in four GSUs were collected from July to November 2014 and evaluated for grain damages, humidity, fungi and fumonisins (FBs) content. The climate conditions data were also obtained from plant growing to storage periods. Regarding the moisture content and water activity (a_w), these varied from 10.0% to 16.1% and 0.5 to 0.8, respectively. As expected, fungi spores were present in 94.8% of the samples, prevailing Fusarium genera, with a fungi colony maximum of 2.2 × 10⁴ CFU g^-1. Regarding FBs, 60.5% of the samples were contaminated, below Brazilian and United States maximum limits, but 9.2% had levels higher than the European legislation.

Safety of low and high cost dry feed intended for dogs in Brazil concerning fumonisins, zearalenone and aflatoxins

The Brazilian pet sector exportation has been growing at an impressive rate lately. Considering the intense globalisation, pet food may be commercialised worldwide and the issue concerning safety of dry dog feed has become a topic of widespread international interest. Therefore, the objectives of this study were to evaluate the safety of low and high cost dry feed and the degree of exposure of dogs to mycotoxins through naturally contaminated feed in Brazil. In addition, the safe pet dietary level (SPDL) was calculated. Fumonisins, zearalenone (ZEA) and aflatoxins were analysed in three feed types intended for dogs (n=87), provided by pet owners. Mean fumonisin levels were 272 µg/kg (Standard), 78.2 µg/kg (Premium), and 186 µg/kg (Super Premium) while ZEA mean levels were 52.6 µg/kg (Standard), 10.6 µg/kg (Premium) and 17.5 µg/kg (Super Premium). Mean total aflatoxin levels (aflatoxin B1 + B2 + G1 + G2) in Standard, Premium and Super Premium feed were 1.29 µg/kg, 0.49 µg/kg and 0.53 µg/kg, respectively. The estimated daily intake (EDI) values for fumonisin B1 were 1.41 (Standard), 1.60 (Premium) and 0.93 µg/kg body weight (BW)/day (Super Premium feed), whereas for ZEA they were 0.54 (Standard), 0.37 (Premium) and 0.42 µg/kg BW/day (Super Premium feed). SPDL for fumonisins and ZEA was 2,000 and 375 µg/kg feed, respectively. EDI values for aflatoxin B1 were 13.0 (Standard), 14.0 (Premium) and 11.0 ng/kg BW/day (Super Premium feed). Although the feed samples intended for dogs in Brazil were often contaminated with aflatoxins, fumonisins and ZEA, the estimated daily intake values were low, even for the low cost formulations. However, it cannot be excluded that some of the feed samples could have a negative effect on animal health and performance considering feeding a monodiet of commercial feed, low multi-mycotoxin contamination levels and interactions between mycotoxins.

The antagonistic effects of Candida parapsilosis on the growth of Fusarium species and fumonisin production

Background and Purpose:

Fusarium species are avid producers of secondary toxic and carcinogenic metabolites such as fumonisin. Contamination of food and feed products with fumonisin can be hazardous to the health of humans and animals and may lead to agricultural loss. Accordingly, in this study, we aimed to evaluate the effects of Candida parapsilosis on the growth and fumonisin production of Fusarium species.

Materials and Methods:

Mycelial growth rate of 26 Fusarium isolates, including F. verticillioides (n=6), F. proliferatum (n=18), F. solani (n=1), and F. oxysporum (n=1), in the presence of 42 C. parapsilosis strains was investigated by pour-plate method. The decline in fumonisin production was measured in co-cultured fungi in coarsely ground maize after four weeks of incubation in the dark at 22°C, using ELISA technique. For data analysis, paired t-test was performed, using SPSS version 20.

Results:

The mycelial growth and fumonisin production of Fusarium isolates significantly decreased in the presence of C. parapsilosis in comparison with the control cultures (P<0.05). The percentage of mycelial growth inhibition ranged from 56.36% to 74.54%. The minimum and maximum decline in total fumonisin production was 12% and 78%, respectively. F. oxysporum and F. solani were found to be minor fumonisin producers among the studied Fusarium species. On the other hand, a decline was reported in the growth of Fusarium species and fumonisin production in the presence of C. parapsilosis.

Conclusion:

C. parapsilosis showed notable inhibitory activities against Fusarium isolates. Therefore, this fungal species could be considered as a biocontrol agent against the growth and fumonisin production of toxigenic Fusarium species in the future.

Light regulation of mycotoxin biosynthesis: new perspectives for food safety

Mycotoxins are secondary metabolites produced by toxigenic fungi contaminating foods and feeds in pre-, post-harvest and processing, and represent a great concern worldwide, both for the economic implications and for the health of the consumers. Many environmental conditions are involved in the regulation of mycotoxin biosynthesis. Among these, light represents one of the most important signals for fungi, influencing several physiological responses such as pigmentation, sexual development and asexual conidiation, primary and secondary metabolism, including mycotoxin biosynthesis. In this review we summarise some recent findings on the effect of specific light wavelength and intensity on mycotoxin biosynthesis in the main toxigenic fungal genera. We describe the molecular mechanism underlying light perception and its involvement in the regulation of secondary metabolism, focusing on VeA, global regulator in Aspergillus nidulans, and the White-Collar proteins, key components of light response in Neurospora crassa. Light of specific wavelength and intensity exerts different effects both on growth and on toxin production depending on the fungal genus. In Penicillium spp. red (627 nm) and blue wavelengths (455-470 nm) reduce ochratoxin A (OTA) biosynthesis by modulating the level of expression of the ochratoxin polyketide synthase. Furthermore a mutual regulation between citrinin and OTA production is reported in Penicillium toxigenic species. In Aspergillus spp. the effect of light treatment is strongly dependent on the species and culture conditions. Royal blue wavelength (455 nm) of high intensity (1,700 Lux) is capable of completely inhibit fungal growth and OTA production in Aspergillus stenyii and Penicillum verrucosum. In Fusarium spp. the effect of light exposure is less effective; mycotoxin-producing species, such as Fusarium verticillioides and Fusarium proliferatum, grow better under light conditions, and fumonisin production increased. This review provides a comprehensive picture on light regulation of mycotoxin biosynthesis and discusses possible new applications of this resource in food safety.

Selection of potential biological control of Exserohilum turcicum with epiphytic microorganisms from maize

The aims of this study were to select microbial isolates from phyllosphere of maize and to examine their antagonistic activity against Exserohilum turcicum. Selection was performed through the ability of isolates to compete with the pathogen using an index of dominance and to affect growth parameters of E. turcicum. Most of the epiphytic populations obtained for the screening were bacteria. These isolates were found in the order of 6 log CFU/g of leaf fresh weight. According to similar morphological characteristics and staining, 44 out of 111 isolates obtained were selected for testing antagonistic effects. At water potential, ψ, -1.38MPa and -4.19MPa, three Bacillus isolates showed dominance at a distance (5/0) and a significant reduction of growth rate of the pathogen. Three Bacillus isolates only decreased the growth rate of E. turcicum at -1.38MPa. At -4.19MPa the growth rate decreased with three isolates of Pantoea and three Bacillus. In this study a negative and significant correlation was observed between the growth rate of E. turcicum and the dominance index in the interaction of the pathogen with some bacteria. These results show that with decreasing growth rate of the pathogen the dominance index of the interaction increases. Eleven potential biocontrol agents against E. turcicum were selected.

Inhibitory Effect of Natural Phenolic Compounds onAspergillus parasiticusGrowth

Considering the impact ofAspergillusspecies on crops, it appears to be highly desirable to apply strategies to prevent their growth, as well as to eliminate or reduce their presence in food products. For this reason, the aims of this investigation were to evaluate the effects of ten natural phenolic compounds on theAspergillus parasiticusgrowth and to determine which physicochemical properties are involved in the antifungal activity. According to the results of minimum inhibitory concentration (MIC) values of the individual compounds, isoeugenol, carvacrol, and thymol were the most active phenolic components (1.26 mM, 1.47 mM, and 1.50 mM, resp.), followed by eugenol (2.23 mM). On the other hand, creosol, p-cresol, o-cresol, m-cresol, vanillin, and phenol had no effects on fungal development. Logarithm of the octanol/water partition coefficient (log P), refractivity index (RI), and molar volume (MV) were demonstrated to be the descriptors that best explained the antifungal activity correlated to lipophilicity, reactivity of the components, and steric aspect. These findings make an important contribution to the search for new compounds with antifungal activity.

Determination of the amount of bioaccessible fumonisin B1 in different matrices after in vitro digestion

Conventional analytical methods used for the analysis of fumonisin content in animal feeds fail to take into account the fumonisin content bound to the matrix, which is otherwise bioaccessible and can be absorbed from the gastrointestinal tract. Moreover, underestimation of fumonisin content using routine analytical methods can affect animal experiments using cereals contaminated by fungi. In the present study, hidden fumonisin B1 was analysed in two cereal substrates (maize and wheat) which were inoculated with Fusarium verticillioides (MRC 826). The study compared a routine extraction procedure with an in vitro digestion sample pre-treatment. We found that all samples showed a higher content of fumonisin B1 after digestion, compared to the free fumonisin obtained only by extraction. The percentage of the hidden form was 38.6% (±18.5) in maize and 28.3% (±17.8) in wheat, expressed as the proportion of total fumonisin B1. These results indicate that the toxin exposure of the animals determined by the routine fumonisin analysis was underestimated, generally by 40%, as bioaccessibility was not taken into consideration. This is crucial in interpretation (and maybe in re-evaluation) of the results obtained from (other) animal experiments.

Integrating toxin gene expression, growth and fumonisin B1 and B2 production by a strain of Fusarium verticillioides under different environmental factors

The objective of this study was to integrate data on the effect of water activity (a(w); 0.995-0.93) and temperature (20-35 °C) on activation of the biosynthetic FUM genes, growth and the mycotoxins fumonisin (FB1, FB2) by Fusarium verticillioides in vitro. The relative expression of nine biosynthetic cluster genes (FUM1, FUM7, FUM10, FUM11, FUM12, FUM13, FUM14, FUM16 and FUM19) in relation to the environmental factors was determined using a microarray analysis. The expression was related to growth and phenotypic FB1 and FB2 production. These data were used to develop a mixed-growth-associated product formation model and link this to a linear combination of the expression data for the nine genes. The model was then validated by examining datasets outside the model fitting conditions used (35 °C). The relationship between the key gene (FUM1) and other genes in the cluster (FUM11, FUM13, FUM9, FUM14) were examined in relation to aw, temperature, FB1 and FB2 production by developing ternary diagrams of relative expression. This model is important in developing an integrated systems approach to develop prevention strategies to control fumonisin biosynthesis in staple food commodities and could also be used to predict the potential impact that climate change factors may have on toxin production.

Practical aspects of fumonisin production under laboratory conditions

Studies were performed to develop an efficient method for fumonisin toxin production in sufficient quantities for animal toxicological experiments, on the basis of three earlier published fumonisin toxin production methods.Three absolutely necessary factors were taken into account and tested in a serial experiment. TheFusarium verticillioides strain MRC 826 was directly inoculated onto soaked, autoclaved, whole maize kernels (50 g/1.71 jar). The inoculation was performed by standard spore suspension (l×l0(6)/ml), a 5/2 surface/volume culture was prepared and incubated at 25 °C for 5 weeks. To maintain the optimal aw of approximately 1.00, the evaporated water was re-filled weekly. A final concentration of 4454±1060.9 ppm fumonisin B1 was reached, with good repeatability. In the laboratory practice, consistent production of constant amounts of FB1 can be obtained by applying the above settings.

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.

Selection of lactic acid bacteria to promote an efficient silage fermentation capable of inhibiting the activity of Aspergillus parasiticus and Fusarium gramineraum and mycotoxin production

AIMS

To select lactic acid bacteria with potential silage inoculant properties. The bio-control activity against mycotoxicogenic fungi and the presence of antibiotics resistance gene were also evaluated.

METHODS AND RESULTS

Lactobacillus rhamnosus RC007 and Lactobacillus plantarum RC009 were selected on the basis of growth rate and efficacy in reducing the pH of maize extract medium; therefore, they were evaluated for their bio-control ability against Fusarium graminearum and Aspergillus parasiticus. Studies on lag phase, growth rate and aflatoxin B1 (AFB1) and zearalenone (ZEA) production were carried out in vitro under different regimes of aw (0·95 and 0·99); pH (4 and 6); temperature (25 and 37°C); and oxygen availability (normal and reduced). Lactobacillus rhamnosus RC007 was able to completely inhibit the F. graminearum growth at all assayed conditions, while Lact. plantarum RC009 only did it at pH 4. Both Lactobacillus strains were able to significantly reduce the A. parasiticus growth rate mainly at 0·99 aw . A decrease in ZEA production was observed as result of Lactobacillus strains -F. graminearum interaction; however, the A. parasiticus- Lact. plantarum interaction resulted in an increased AFB1 production. Lactobacillus rhamnosus RC007 proved to have no genes for resistance to the tested antibiotics.

CONCLUSIONS

The ability of Lact. rhamnosus RC007 to rapidly drop the pH and to inhibit fungal growth and mycotoxin production and the absence of antibiotic resistance genes shows the potential of its application as inoculant and bio-control agent in animal feed.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrated the importance of selecting bacteria for silage inoculants not only for the improvement of silage fermentation but also for their effects on mycotoxicogenic fungi and the resulting mycotoxin production due to the risk that they may involve.

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.

FUM and BIK gene expression contribute to describe fumonisin and bikaverin synthesis in Fusarium verticillioides

Fusarium verticillioides is a maize pathogen that produces toxic secondary metabolites, including fumonisins and bikaverin. The regulation of biosynthetic gene expression and the production of these metabolites are not fully understood and in this study we investigated the influence of water activity (0.955 and 0.990) on the expression of 5 genes (FUM3-FUM8-FUM13-FUM14 and BIK1) in F. verticillioides strains after 14 and 21days incubation. Fumonisin production and biosynthetic gene expression were greatest at a(w)=0.990, and the same trend was observed for bikaverin production, and BIK1 expression. FUM3 and FUM14 were the most highly expressed genes and were positively correlated with the production of FB(1), FB(2) and FB(3). When FUM14 is more highly expressed than FUM3 the amount of FB(3) quantified is higher with respect to FB(1); this could be explained by the role of FUM3 in the hydroxylation of FB(3) to FB(1).

Fumonisins B, A and C profile and masking in Fusarium verticillioides strains on fumonisin-inducing and maize-based media

The production of fumonisin B, A and C and hidden and partially hydrolysed fumonisin occurrence was investigated in 3 strains of Fusarium verticillioides isolated from maize, cultured for 21-45days on malt extract medium at 25°C and 0.955-0.990 water activity (a(w)). Fumonisin A-B and C series were produced by all the strains in all conditions studied, with B-fumonisin≫C-fumonisin>A-fumonisin following a similar trend. The dynamic of fumonisin production was significantly influenced by factors considered and their interaction, with a(w)=0.990 as favourable condition in ITEM 10026 and ITEM 10027. All fumonisins were maximised at 30days incubation in ITEM 10027 and ITEM 1744 and at 45days incubation in ITEM 10026. Partially hydrolysed fumonisins were detected only for the B-group. Hidden fumonisins were never observed in Fusarium cultures grown on malt extract medium but were detected in the additional trial on maize-based medium, suggesting that the masking phenomenon can occur only in a complex matrix.

Saccharomyces cerevisiae strains and the reduction of Aspergillus parasiticus growth and aflatoxin B1 production at different interacting environmental conditions, in vitro

The effect of Saccharomyces cerevisiae RC008 and RC016, previously selected based on their aflatoxin B(1) binding ability and beneficial properties, against Aspergillus parasiticus under different interacting environmental conditions was evaluated. Studies concerning the lag phase, growth rate and aflatoxin B(1) production were carried out in vitro under different regimes of a (w) (0.95 and 0.99), pH (4 and 6), temperature (25 and 37°C), and oxygen availability (normal and reduced). Both yeast strains showed great antagonistic activity at pH 4, decreasing growth rate compared with the control. The RC008 strain showed the greatest inhibitory activity at all assayed conditions. A. parasiticus produced large amounts of AFB(1) in vitro. A significant decrease of AFB(1) levels in comparison with the control were observed with yeast interaction. Differences between control and treatment values ranged from 130 to 5400 ng ml(-1). S. cerevisiae RC008 and RC016 could be considered as effective agents in reducing growth and AFB(1) production at different interacting environmental conditions, related to that found in stored feedstuff. The importance of the present work lies in the search for live strains with both probiotic and biocontrol properties able to prolong the safe storage of feedstuff and exert beneficial properties after animal consumption and which could be included in a novel product for animal feed.

Fumonisin B1, a toxin produced by Fusarium verticillioides, modulates maize β-1,3-glucanase activities involved in defense response

Fusarium verticillioides is an important pathogen in maize that causes various diseases affecting all stages of plant development worldwide. The fungal pathogen could be seed borne or survive in soil and penetrate the germinating seed. Most F. verticillioides strains produce fumonisins, which are of concern because of their toxicity to animals and possibly humans, and because they enhance virulence against seedlings of some maize genotypes. In this work, we studied the action of fumonisin B1 (FB1) on the activity of maize β-1,3-glucanases involved in plant defense response. In maize embryos, FB1 induced an acidic isoform while suppressing the activity of two basic isoforms. This acidic isoform was induced also with 2,6-dichloroisonicotinic acid, an analog of salicylic acid. Repression of the basic isoforms suggested a direct interaction of the enzymes with the mycotoxin as in vitro experiments showed that pure FB1 inhibited the basic β-1,3-glucanases with an IC(50) of 53 μM. When germinating maize embryos were inoculated with F. verticillioides the same dual effect on β-1,3-glucanase activities that we observed with the pure toxin was reproduced. Similar levels of FB1 were recovered at 24 h germination in maize tissue when they were treated with pure FB1 or inoculated with an FB1-producing strain. These results suggest that β-1,3-glucanases are a relevant physiological target and their modulation by FB1 might contribute to F. verticillioides colonization.

Fusarium verticillioides: evaluation of fumonisin production and effect of fungicides on in vitro inhibition of mycelial growth

The objectives of this study were to evaluate the fumonisin production by 16 F. verticillioides strains on corn cultures and the effect of quintozene and fludioxonil + metalaxyl-M fungicides on "in vitro" mycelial growth on agar. In addition, the effect of fludioxonil + metalaxyl-M on fumonisin production in defined liquid culture medium was analyzed. Fumonisin B(1) levels on corn cultures ranged from 2.41 to 3996.36 μg/g and the F. verticillioides 103F strain produced the highest level (3996.36 ± 390.49 μg/g, P < 0.05). F. verticillioides strains were inoculated in potato dextrose agar with the addition of quintozene (75 to 9,375 μg/ml) and fludioxonil + metalaxyl-M (1.5 + 0.6 to 187.5 + 75 μg/ml) in order to evaluate the effect of these fungicides on "in vitro" mycelial growth. The F. verticillioides strains showed great variability concerning ED(50) values, which were below the recommended application dose for quintozene, but above that for fludioxonil + metalaxyl-M. Moreover, fungicide addition to the culture medium increased mean FB(1) levels compared to the control, suggesting the importance of focusing on the effect of fungicides on mycotoxin production as well as on the phytopathogen control.

Effect of antioxidant mixtures on growth and ochratoxin a production of Aspergillus section Nigri species under different water activity conditions on peanut meal extract agar

The effect of mixtures of antioxidants butylated hydroxyanisol (BHA) and propyl paraben (PP) on lag phase, growth rate and ochratoxin A (OTA) production by four Aspergillus section Nigri strains was evaluated on peanut meal extract agar (PMEA) under different water activities (a(w)). The antioxidant mixtures used were: BHA + PP (mM), M1 (0.5 + 0.5), M2 (1.0 + 0.5), M3 (2.5 + 0.5), M4 (0.5 + 1.0), M5 (1.0 + 1.0), M6 (2.5 + 1.0), M7 (5.0 + 2.5) and M8 (10 + 2.5). The mixture M8 completely suppressed mycelial growth for all strains. A significant stimulation in OTA production was observed with mixtures M1 to M5 mainly at the highest a(w); whereas M6, M7 and M8 completely inhibited OTA production in all strains assayed; except M6 in A. carbonarius strain (RCP G). These results could enable a future intervention strategy to minimize OTA contamination.

Use of propyl paraben to control growth and ochratoxin A production by Aspergillus section Nigri species on peanut meal extract agar

This study was carried out to determine the efficacy of the phenolic antioxidant propyl paraben (PP) under different interacting water activity (a(W)) and temperature regimes on lag phase, growth rate and Ochratoxin A production by Aspergillus section Nigri strains. In this experiment six Aspergillus section Nigri strains were used. Peanut meal extract agar (PMEA) was prepared at 2%. The a(W) of the medium was adjusted to 0.995, 0.980 and 0.930, PP levels of 1, 5, 10 and 20 mmol/L were added to the basic medium. Plates were inoculated and incubated for 30 days at 18 and 25 degrees C. Lag phase (h) and radial growth rates (mm/day) were calculated. In control treatments, the lag phase increased and the growth rate decreased as a(W) reduced in all assayed strains. At all a(W) levels, when antioxidant concentrations increased the growth rate decreased. At 5, 10 and 20 mmol/L of PP the strains were not able to reach the exponential phase and completely inhibited fungal growth and OTA production regardless of a(W) used in all the evaluated strains.

Environmental factors modify carbon nutritional patterns and niche overlap between Aspergillus flavus and Fusarium verticillioides strains from maize

This study examined the utilization patterns of key carbon sources (CS, 24: including key sugars, amino acids and fatty acids) in maize by strains of Aspergillus flavus and Fusarium verticillioides under different water activity (a(w), 0.87-0.98 a(w)) and temperature (20-35 degrees C) values and compared the niche overlap indices (NOI) that estimate the in vitro CS utilization profiles [Wilson, M., Lindow, S.E., 1994. Coexistence among epiphytic bacterial populations mediated through nutritional resource partitioning. Applied and Environmental Microbiology 60, 4468-4477.]. The ability to grow in these key CS in minimal media was studied for 120 h in 12 h steps. The NOI was calculated for inter-species (F. verticillioides-A. flavus) and for intra-species (A. flavus-A. flavus) using CS utilization patterns over the range of interacting environmental conditions. 30 degrees C, over the whole a(w) range examined, was found to be optimal for utilization of the maximum number of CS by A. flavus. In contrast, for F. verticillioides this was more so at 20 degrees C; 25 degrees C allowed a suboptimal usage of CS for both species. NOIs confirmed the nutritional dominance of A. flavus at 30 degrees C, especially at lower a(w) levels and that of F. verticillioides at 20 degrees C, mainly at 0.95 a(w). In other conditions of a(w), based on CS utilization patterns, the data indicated that A. flavus and F. verticillioides occupied different ecological niches. The variability in nutritional sources utilization between A. flavus strains was not related to their ability to produce aflatoxins (AFs). This type of data helps to explain the nutritional dominance of fungal species and strains under different environmental conditions. This could be useful in trying to find appropriate natural biocontrol microorganisms to compete with these mycotoxigenic species.

Fumonisins, trichothecenes and zearalenone in cereals

Fumonisins are phytotoxic mycotoxins which are synthesized by various species of the fungal genus Fusarium such as Fusarium verticillioides (Sacc.) Nirenberg (ex F.moniliforme Sheldon) and Fusarium proliferatum. The trichothecene (TC) mycotoxins are secondary metabolites produce by species that belong to several fungal genera, especially Fusarium, Stachybotrys, Trichothecium, Trichoderma, Memnoniella and Myrothecium. Fusarium mycotoxins are widely dispersed in cereals and their products. Zearalenone (ZEA) is an estrogenic compound produced by Fusarium spp. such as F. graminearum and F. culmorum. Fumonisins, the TCs and ZEA are hazardous for human and animal health. Contamination with TCs causes a number of illnesses in human and animal such as decrease in food consumption (anorexia), depression or inhibition on immune system function and haematoxicity. The purpose of this paper is to give a review of the papers published on the field of fumonisin, TC and ZEA mycotoxins in cereals consumed in the world.

Influence de l’interaction de la température et de l’activité de l’eau sur la croissance et la production de l’ochratoxine A parAspergillus niger,Aspergillus carbonariusetAspergillus ochraceussur un milieu de base café

Dans cette étude, l’influence de l’interaction de la température et de l’activité de l’eau sur la croissance fongique et la production de l’ochratoxine A sur un milieu de base café a été évaluée. La croissance optimale des trois souches d’ Aspergillus a été observée dans les mêmes conditions écologiques à savoir, 30 °C pour la température et 0,99 pour l’activité de l’eau. Les croissances journalières maximales sont 11,2, 6,92 et 7,22 mm/jour respectivement pour la souche d’Aspergillus niger, d’Aspergillus carbonarius et d’Aspergillus ochraceus. Cependant, les conditions écologiques de production optimale d'ochratoxine A varient selon la souche toxinogène avec comme facteur limitant, l’activité de l’eau. Cette production d’ochratoxine A est inhibée à la température de 42 °C et à l’activité de l’eau de 0,75. La correspondance établie entre les valeurs d’activité de l’eau testées en laboratoire et celles mesurées sur un lot de cerises mûres mis à sécher au soleil montre que les 5 premiers jours de séchage constituent la phase critique de multiplication fongique et de production de l’ochratoxine A. Ainsi, un séchage artificiel des cerises à une température supérieure à 42 °C évitera non seulement la multiplication fongique mais également la contamination de ce produit par l’ochratoxine A.

Studies on Aspergillus section Flavi isolated from maize in northern Italy

In 2003, for the first time in Italy, significant problems arose with colonization and contamination of maize destined for animal feed with Aspergillus section Flavi and aflatoxins (AFs). This resulted in milk and derived products being contaminated with AFM(1) at levels above the legislative limit. There was little knowledge and experience of this problem in Italy. The objectives of this research were thus to study the populations of Aspergillus section Flavi in six northern Italian regions and obtain information on the relative role of the key species, ability to produce sclerotia, production of the main toxic secondary metabolites, aflatoxins and cyclopiazonic acid, and tolerance of key environmental parameters. A total of 70 strains were isolated and they included the toxigenic species A. flavus and A. parasiticus. A. flavus was dominant in the populations studied, representing 93% of the strains. Seventy percent of strains of Aspergillus section Flavi produced AFs, with 50% of strains also producing cyclopiazonic acid. Sixty-two percent of A. flavus strains and 80% of A. parasiticus were able to produce sclerotia at 30 degrees C. Using 5/2 agar, only 1 strain developed S sclerotia and 19 L sclerotia. With regard to ecological studies, growth of Aspergillus section Flavi was optimal at between 25 and 30 degrees C, while AFB(1) production was optimal at 25 degrees C. Regarding water availability (water activity, a(w)), 0.99 a(w) was optimal for both growth and AFs production, while the only aflatoxin produced in the driest condition tested (0.83 a(w)) was AFB(1). This information will be very useful in identifying regions at risk in northern Italy by linking climatic regional information to levels of fungal contamination present and potential for aflatoxin production in maize destined for animal feed. This would be beneficial as part of a prevention strategy for minimising AFs in this product.

Predictive modelling of temperature and water activity (solutes) on the in vitro radial growth of Botrytis cinerea Pers

The objective of this work was to develop validated models predicting the 'in vitro' effect of a(w) and temperature on the radial growth of Botrytis cinerea. The growth rate (g, mm d(-1)) of B. cinerea was calculated at three incubation temperatures (25 degrees C, 15 degrees C, 5 degrees C) and six water activities (ranging from 0.995 to 0.890). The water activity was adjusted with glucose, NaCl, glycerol, or sorbitol. Statistical analysis showed a significant effect of temperature, solute, a(w), and their two- and three-way interactions on the growth rate. No growth was observed at a(w)=0.93 in the presence of NaCl or at 0.89 in the presence of a non-ionic solute. The maximum colony growth rate decreased when the incubation temperature and water activity was lowered. Secondary models, relating the colony growth rate with a(w) or a(w) and temperature were developed. Optimum a(w) values for growth ranged from 0.981 to 0.987 in glycerol-, sorbitol-, or glucose-modified medium and were close to 1 in NaCl-modified medium. A quadratic polynomial equation was used to describe the combined effects of temperature and a(w) on g (mm d(-1)) in the presence of each solute. The highest and lowest radial growth rates were observed in models based on glucose and NaCl respectively, whatever the incubation temperature. All models prove to be good predictors of the growth rates of B. cinerea within the limits of experiments. The quadratic polynomial equation has bias factors of 0.957, 1.036, 0.950, and 0.860 and accuracy factors of 1.089, 1.070, 1.120 and 1.260 in media supplemented with glucose, NaCl, glycerol and sorbitol respectively. The results from modelling confirm the general finding that a(w) has a greater influence on fungal growth than temperature.

Distribution and elimination of fumonisin analogues in weaned piglets after oral administration of Fusarium verticillioides fungal culture

The distribution and elimination of fumonisins after oral administration of 50 mg FB(1), 20 mg FB(2) and 5 mg FB(3) per animal day(-1) for 22 days was studied in weaned barrows. At the end of the trial, the lung, heart, liver, kidney, spleen, brain, serum, bile, muscle, fat, urine and faeces samples were collected and their content of fumonisins (FB(1), FB(2)) determined by LC-MS. The highest FB(1) concentrations were found in the liver (99.4 +/- 37.5 ng g(-1)) and kidneys (30.6 +/- 10.1 ng g(-1)), whilst the highest average amount of FB(2) was in the liver (1.4 +/- 2.3 ng g(-1)) and fat (2.6 ng g(-1) +/- 4.8) samples. Comparing the FB(1)/FB(2) ratio in different organs (19/1), it was found that the ratio in the abdominal and subcutaneous fat samples (4/1) was markedly different from those in all other tissues, namely the relative proportion of FB(2) was higher in latter cases. Of the total quantity of FB(1), the 13% taken up during 5 days was excreted unchanged with the faeces and urine. On average, in the urine and faeces, FB(1) was detected in nine- and 14-fold quantities, as compared with FB(2).

Growth kinetics of cultures from single spores of Aspergillus flavus and Fusarium verticillioides on yellow dent corn meal

A dilution protocol originally developed for the isolation of single bacterial cells was modified to suite the specificities of fungal growth. The modified protocol was used to study the growth kinetics of single spores of Aspergillus flavus and Fusarium verticillioides on yellow dent corn meal. Both a(w) and temperature significantly influenced the distributions of the colony growth rates and lag phases and the rate at which individual spores of both isolates completed the lag period. An interaction between a(w) and temperature was noted on the spread of the distributions of these growth parameters. The histograms of the single spore colony growth rates and lag phases generally became wider the more compromising the conditions for growth became, indicating a greater variation in growth ability at these conditions. The rate at which the single spores passed through the lag phases generally decreased with decrease in temperature and/or a(w), with an interaction again noted between these two factors on the rate. These results show the potential range and variability in growth of individual fungal spores at the lowest inoculum level possible.

Control of Aspergillus growth and aflatoxin production using natural maize phytochemicals under different conditions of water activity

The effects of the natural phytochemicals trans-cinnamic acid (CA) and ferulic acid (FA) alone at concentrations of 1-25 mM and in 16 combinations (M: mixtures) on growth and aflatoxin B(1) production by Aspergillus flavus Link and A. parasiticus Speare were evaluated. Studies on growth rate and aflatoxin B(1) production were carried out in vitro in relation to a water activity a(w) of 0.999, 0.971, 0.955 and 0.937. Overall, CA at concentrations of 10 and 20 mM and FA-CA mixtures M3 (20 + 5 mM respectively), M8 (25 + 5 mM), M9 (1 + 10 mM), M10 (10 + 10 mM), M11 (20 + 10 mM), M12 (25 + 10 mM), M13 (1 + 20 mM), M14 (10 + 20 mM), M15 (20 + 20 mM) and M16 (25 + 20 mM) were the treatments most effective at inhibiting growth of the four species assayed. All strains were much more sensitive to all natural phytochemicals tested on growth rate at a(w) = 0.937. CA and the FA-CA mixtures M1 (1 + 1 mM respectively), M4 (25 + 1 mM), M5 (1 + 5 mM), M6 (10 + 1 mM), M7 (20 + 1 mM), M8 (25 + 5 mM), M9 (1 + 10 mM), M10 (10 + 10 mM), M11 (20 + 10 mM), M12 (25 + 10 mM), M13 (1 + 20 mM), M14 (10 + 20 mM), M15 (20 + 20 mM) and M16 (25 + 20 mM) completely inhibited aflatoxin B(1) production by all strains at a(w) = 0.999, 0.971, 0.955 and 0.937. Decreased aflatoxin B(1) levels in comparison with the control were observed with FA at 1, 10, 20 and 25 mM with the strains RCM89, RCM108 and RCM38 at a(w) = 0.971, 0.955 and 0.999 respectively. The data show that CA and FA can be considered as effective fungitoxicants for A. flavus and A. parasiticus in in vitro assay. The information obtained is part of an ongoing study to determine their application at the storage level.

Fumonisin production in rice cultures of Fusarium verticillioides under different incubation conditions using an optimized analytical method

Fumonisin B1 (FB1) and fumonisin B2 (FB2) are the main members of a family of mycotoxins produced by various fungal species belonging to the Gibberella fujikuroi complex. The present work shows the results of a comparative study of various clean-up and derivatization procedures for analysis of fumonisins in rice cultures. Fumonisins were extracted from rice with acetonitrile/water (50/50, v/v). For clean-up, three solid-phase extraction procedures were assayed (C18 cartridge, SAX cartridge, and a combination of both). Two reagents (o-phthaldialdehyde and 4-fluoro-7-nitro-benzofurazan) were studied comparatively for formation of fluorescent derivatives. The separation was carried out by LC using a fluorescence detector. The best procedure for analysis of fumonisins in rice involved clean-up with C18 cartridge and derivatization with o-phthaldialdehyde. The limit of detection was 0.010 mg kg(-1) for both toxins. In the 10-500 mg kg(-1) spiking level range, the recovery rates for FB1 and FB2 in rice varied from 94.6% to 103.6% and from 96.3% to 101.9%, respectively. The optimized analytical method for determination of fumonisins in rice was applied to the study of FB1 and FB2 production by four isolates of the G. fujikuroi species complex in rice cultures carried out at different temperatures and water activities to establish the influence of strain and environmental conditions on fumonisin production in this cereal. In general, fumonisin production was the highest at 20 degrees C and lowest at 37 degrees C. Four of the five assayed water activity (aw) values (0.97, 0.98, 0.99, and 1.0) did not affect significantly fumonisin accumulation but fumonisins were not detected in cultures when aw was 0.96.

Temperature and water activity effects on growth and temporal deoxynivalenol production by two Argentinean strains of Fusarium graminearum on irradiated wheat grain

The objective of this study was to determine the effects of water activity (a(W); 0.900-0.995), temperature (5, 15, 25 and 30 degrees C), time of incubation (7-49 days) and their interactions on mycelial growth and deoxynivalenol (DON) production on irradiated wheat grain by two strains of Fusarium graminearum isolated from wheat ears in Argentina. Optimal a(W) levels for growth were in the range 0.950-0.995 with a temperature optima of 25 degrees C. Maximum growth rates were obtained at the highest a(W) (0.995) and 25 degrees C for both strains. No growth was observed at 5 degrees C regardless of the a(W) levels assayed. Both strains were able to growth at the lowest a(W) assayed (0.900), although the temperature ranges allowing growth at this minimal a(W) was 15-25 degrees C. DON was produced the most rapidly (7 days) when incubated at 25 degrees C and 0.995 a(W). All other conditions required 7-14 days before DON was produced on grain. Maximum amounts of DON for both strains were produced at the highest a(W) treatment (0.995) after 6 weeks at 30 degrees C. The range of DON concentrations varied considerably (5 to 140,000 ng g(-1)) depending on a(W) and temperature interaction treatments. Production of DON occurred over a narrower range of a(W) (0.995-0.95) than that for growth (0.995-0.90). DON was more rapidly produced at 25 degrees C but the maximum amount produced was at 30 degrees C. Two-dimensional profiles of a(W) x temperature were developed from these data to identify areas where conditions indicate a significant risk from DON accumulation.

Detection of new fumonisin mycotoxins and fumonisin-like compounds by reversed-phase high-performance liquid chromatography/electrospray ionization ion trap mass spectrometry

Fumonisins were produced in a rice culture infected with Fusarium verticillioides. To decrease the possibility of the formation of artifacts, the fumonisins were analyzed by reversed-phase high-performance liquid chromatography with electrospray ionization ion trap tandem mass spectrometry (RP-HPLC/ESI-IT-MS2) immediately after the extraction of the culture material without any sample clean-up. In addition to already known fumonisins, numerous new fumonisin mycotoxins and fumonisin-like compounds were detected. On the basis of the IT-MS2 data, detailed fragmentation pathways including new mechanisms were proposed for the different series of fumonisins. The retention times, the masses of the protonated molecules and of the product ions including the backbones and the characteristic neutral mass losses from the protonated molecules of the new compounds suggested their structures (applying the well-known designation): iso-FA1a,b, iso-FB1a-d, iso-FB2,3a-e, PHFB2a-c, PHFB4a-d, FB5/iso-FB5a-d, FBK1 2TCA, FBK4 2TCA, FC2, iso-FC2,3, PHFC4, FD and FBX series. The relative quantities of fumonisins and fumonisin-like compounds found in the sample extract were expressed as percentages of FB1 (0.02-100%). The backbone of the compound denoted FD contained fewer carbon atoms than the well-known fumonisins with the C19 or C20 backbone and may well be a precursor of the longer compounds. For the compounds denoted FBX (12 compounds), one or two OH groups attached to the fumonisin backbone were esterified by carboxylic acids other than tricarballylic acid, such as cis-aconitic acid, oxalylsuccinic acid and oxalylfumaric acid.