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The aim of this study was to evaluate the interactions between wheat plant (spikelets and straws), a strain of mycotoxigenic pathogen Fusarium graminearum and commercial biocontrol agents (BCAs). The ability of BCAs to colonize plant tissue and inhibit the pathogen or its toxin production was observed throughout two phases of the life cycle of pathogens in natural conditions (colonization and survival). All evaluated BCAs showed effective reduction capacities of pathogenic traits. During establishment and the expansion stage, BCAs provoked an external growth reduction of F. graminearum (77–93% over the whole kinetic studied) and mycotoxin production (98–100% over the whole kinetic studied). Internal growth of pathogen was assessed with digital droplet polymerase chain reaction (ddPCR) and showed a very strong reduction in the colonization of the internal tissues of the spikelet due to the presence of BCAs (98% on average). During the survival stage, BCAs prevented the formation of conservation perithecia of the pathogen on wheat straw (between 88 and 98% of perithecia number reduction) and showed contrasting actions on the ascospores they contain, or perithecia production (−95% on average) during survival form. The mechanisms involved in these different interactions between F. graminearum and BCAs on plant matrices at different stages of the pathogen’s life cycle were based on a reduction of toxins, nutritional and/or spatial competition, or production of anti-microbial compounds.

The aim of this study was to develop a set of experiments to screen and decipher the mechanisms of biocontrol agents (BCAs), isolated from commercial formulation, against two major mycotoxigenic fungi in cereals, Fusarium graminearum and Fusarium verticillioides. These two phytopathogens produce mycotoxins harmful to human and animal health and are responsible for the massive use of pesticides, for the protection of cereals. It is therefore essential to better understand the mechanisms of action of alternative control strategies such as the use of BCAs in order to optimize their applications. The early and late stages of interaction between BCAs and pathogens were investigated from germination of spores to the effects on perithecia (survival form of pathogen). The analysis of antagonist activities of BCAs revealed different strategies of biocontrol where chronological, process combination and specialization aspects of interactions are discussed. Streptomyces griseoviridis main strategy is based on antibiosis with the secretion of several compounds with anti-fungal and anti-germination activity, but also a mixture of hydrolytic enzymes to attack pathogens, which compensates for an important deficit in terms of spatial colonization capacity. It has good abilities in terms of nutritional competition. Trichoderma asperellum is capable of activating a very wide range of defenses and attacks combining the synthesis of various antifungal compounds (metabolite, enzymes, VOCs), with different targets (spores, mycelium, mycotoxins), and direct action by mycoparasitism and mycophagy. Concerning Pythium oligandrum, its efficiency is mainly due to its strong capacity to colonize the environment, with a direct action via microbial predation, stimulation of its reproduction at the contact of pathogens and the reduction of perithecia formation.

Wild yeasts isolated from the surface of apples were screened for antagonistic activity against Penicillium expansum, the main producer of the mycotoxin patulin. Three antagonistic yeasts (Y33, Y29 and Y24) from a total of 90 were found to inhibit P. expansum growth. Identification by ITS region sequence and characterization showed that three selected isolates of yeast should be different strains of Metschnikowia pulcherrima. Several concentrations of the selected yeasts were used to study their in vitro antifungal effectivity against P. expansum on Petri dishes (plates with 63.6 cm2 surface) whereas their potential activity on patulin reduction was studied in liquid medium. Finally, the BCA that had the best in vitro antifungal capacity against P. and the best patulin degradation capacity was selected to be assessed directly on apples. All the selected strains demonstrated antifungal activity in vitro but the most efficient was the strain Y29. Isolated strains were able to reduce patulin content in liquid medium, Y29 being the only strain that completely reduced patulin levels within 120 h. The application of Y29 as biocontrol agent on the surface of apples inoculated with P. expansum, inhibited fungal growth and patulin production during storage. Therefore, the results shown that this yeast strain could be used for the reduction of P. expansum and its mycotoxin in apples or apple-based products by adapting the procedure application., The authors acknowledge the financial support of the Agence Nationale de la Recherche (France) (PATRISK project: ANR-17-CE21-0008) and the financial support of the European Union (Erasmus grant attributed to Laura Settier-Ramírez).

Fungal pathogens are an international concern regarding their impact on numerous crops with diseases such as the Fusarium wilt, grey molds, blue molds or downy mildews that cause colossal yield losses both at pre- and post-harvest stages all over the world. The fungal diseases are usually associated with the infection and accumulation of mycotoxins in plant products and derivate foods. Alternative approaches of biological control that are non-chemical and eco-friendly have been studied such as the crop rotations or the application of organic phyto-protective amendments using living organisms. Many different bacterial families have been identified but accounting for low abundance in the total communities. The participation of the predominant families in 3-day-old soil decreased after 28 days of incubation. The fungal community of the reference soil was more diversified as compared to the fungal communities of the amendments.

Ochratoxin A (OTA) is a secondary metabolite produced by fungal pathogens such as Penicillium verrucosum, which develops in food commodities during storage such as cereals, grapes, and coffee. It represents public health concerns due to its genotoxicity, carcinogenicity, and teratogenicity. The objective of this study was to evaluate the ability of actinobacteria and their metabolites to degrade OTA and/or to decrease its production. Sixty strains of actinobacteria were tested for their ability to prevent OTA formation by in vitro dual culture assays or with cell free extracts (CFEs). In dual culture, 17 strains strongly inhibited fungal growth, although it was generally associated with an increase in OTA specific production. Seventeen strains inhibited OTA specific production up to 4% of the control. Eleven actinobacteria CFEs reduced OTA specific production up to 62% of the control, while no substantial growth inhibition was observed except for two strains up to 72% of the control. Thirty-three strains were able to degrade OTA almost completely in liquid medium whereas only five were able to decrease it on solid medium, and two of them reduced OTA to an undetectable amount. Our results suggest that OTA decrease could be related to different strategies of degradation/metabolization by actinobacteria, through enzyme activities and secretion of secondary metabolites interfering with the OTA biosynthetic pathway. CFEs appeared to be ineffective at degrading OTA, raising interesting questions about the detoxification mechanisms. Common degradation by-products (e.g., OT&alpha, or L-&beta, phenylalanine) were searched by HPLC-MS/MS, however, none of them were found, which implies a different mechanism of detoxification and/or a subsequent degradation into unknown products.

In a sustainable development concern, the agricultural practices notably those to control the pathogenic and/or mycotoxigenic fungi that maintain the quality and the abundance of crops with respecting the ecosystems and public health are indispensable. Our study focuses on evaluating the biocontrol potential of the actinomycete microflora of some organic amendments against the phytopathogenic and mycotoxigenic Fusarium verticillioides. The inhibitory effect was assessed in term of growth and mycotoxin production (fumonisin FB1 and FB2) of F. verticillioides in the presence of amended soils and selected antagonist agents from the amendments. Results demonstrated that the amended soils with different organic amendments exhibited a higher inhibition rate of Fusarium verticillioides growth than the reference soil. They were able to inhibit the fungal pigment and spore productions which are the major mean of survival and dispersion of this fungus. The fumonisin production was strongly reduced by the metabolites produced by the amended soils’ microbiota, up to 68.7% and 92.5% for FB1 and FB2 respectively. Actinomycete strains isolated from these amendments were identified as Streptomyces and were also tested for their antifungal potential. The fungal growth was reduced up to more than 60% in the presence of extracellular metabolites of several Streptomyces strains. In confrontation assays, most of the Streptomyces strains inhibited strongly both fungal growth and fumonisin production. The FB1 and FB2 amounts were decreased at best, by up to 87.5% and 98.2% respectively, depending on the actinomycete strains and fungal culture time. These results are promising for the use of these biocontrol agents, and especially some actinomycete strains, as tools to reduce fumonisin contamination in cereal crops and derived products.

Cereals products enriched with leguminous or oleaginous are used in Burkina Faso as food complement or to avoid infant malnutrition. Infant formulas from cereals are consumed as food supplements after the weaning age. They are produced in Burkina Faso with a mixture of several cereals (maize, millet, rice, or sorghum), leguminous (bean), oleaginous (peanut, soya or sesame), sugar or salt and sometimes milk powder. The production is artisanal or semi-industrial. These infant foods from cereals should be free from mycotoxins and pathogenic bacteria. The objective of this work was to determine the occurrence of mycotoxins like aflatoxins, ochratoxin A and fumonisins in infant formulas and grains in Ouagadougou (Burkina Faso). The mycotoxins (aflatoxins, ochratoxin A and fumonisins) were determined by HPLC-FLD in 248 samples of infant formulas produced by the Recovery and Nutrition Education Centers (CRENs) and sold on the market places in Burkina Faso. Results showed that the majority of samples of infant formulas presented high levels of mycotoxins. The frequency of contaminated samples by aflatoxin B1, ochratoxin A and fumonisins in analyzed samples were 83.9% (167/199), 7.5% (15/199) and 1.5% (3/199), respectively. The highest values registered in infant formulas were 900, 6 and 3 times higher for aflatoxin B1 (EU limit: 0.1 μg/kg), ochratoxin A (EU limit: 0.5 μg/kg) and fumonisins (EU limit: 200 μg/kg), respectively, than the EU regulation limits (1881/2006). This study presents the first results concerning the safety assessment of infant formulas regarding mycotoxins in Burkina Faso.

International audience; The Streptomyces sp. strain AV05 isolated from an organic amendment was found to impact both growth and fumonisin production of Fusarium verticillioides during in vitro direct confrontation. In order to investigate the interactions between the Streptomyces sp. strain AV05 and F. verticillioides, a metabolomic approach was used. The study of the endometabolomes of the microorganisms was carried out in two different conditions: the microorganisms were cultivated alone or in confrontation. The aim of this study was to examine the modifications of the endometabolome of F. verticillioides in confrontation with the Streptomyces strain. The metabolites involved in these modifications were identified using 2D NMR. Many metabolites were found to be overproduced in confrontation assays with the Streptomyces strain, notably 16 proteinogenic amino acids, inosine, and uridine. This suggested that fungal metabolic pathways such as protein synthesis have been affected due to interaction. Thus, metabolomic studies, as well as proteomics or transcriptomics, are useful for deciphering the mechanisms of interactions between biological control agents and mycotoxigenic fungi. This comprehension is one of the key elements of the improvement of the selection and use of antagonistic agents.

'Kankankan' is a popular spice powder used to season roasted meat in Côte d'Ivoire. However, produced in a traditional way, the conditions of production and storage of kankankan favour the proliferation of mycotoxin-producing fungal strains. The aim of this study was to carry out an inventory of mycotoxin contamination of this spice powder and to assess risk exposure to consumers. In total, 75 samples of kankankan were collected from wholesalers (6), sellers of kankankan in the markets (35) and sellers of roasted meat (34) across three municipalities of Abidjan, the economic capital of Côte d'Ivoire. Ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was used to detect and quantify nine different mycotoxins. Dietary exposure was calculated by using estimated daily intake (EDI), whereas risk characterisation was assessed using the margin of exposure (MOE) approach. Aflatoxins and fumonisins were found in 99% of samples assessed, while contamination with beauvericin was proportionally lowest (28%). At all the three types of actors within the food production chain (wholesalers, kankankan sellers and roasted meat sellers) the mean concentrations of aflatoxin B1 (AFB1) in samples exceeded the European standard for spice mixtures, with concentrations reaching up to 502 µg/kg. The estimated daily intakes of aflatoxins observed in the different populations were above the recommended level of 0.017 ng kg−1 b.w. day−1. The MOES values for adolescents and adults were 8.10 and 12.78, respectively, well below the safe margin of 10,000. The co-occurrence of mycotoxins in kankankan samples together with high aflatoxin exposure to consumers represent a potential risk to public health, calling for immediate risk management and education of kankankan producers and consumers.

The current study assesses the natural occurrence of mycotoxins and fungal metabolites in Tunisian Pearl millet. Investigations using a multi-mycotoxin liquid chromatography/electrospray ionization-tandem mass spectrometric (LC/ESI–MS/MS) method were carried out on a total of 220 pearl millet samples collected from farmers (n = 144) located in four different agroecological zones in Tunisia and from retail shops (n = 76). Results revealed fifty-seven regulated and emerging metabolites contaminating 91.4% of grain samples. Among major mycotoxins, both aflatoxin B1 (AFB1) and ochratoxin A (OTA) were the most prevalent at rate of 8.6% each and occurring at an average level of 106 and 69.4 μg/kg, respectively. All positives samples were significantly exceeding the European thresholds (5 and 3 μg/kg, respectively). Lower incidence (5.9%) of Zearalenone (ZEA) contaminated samples at levels below the authorized limits (100 μg/kg) was recorded. Pearl millet grains from the south coastal zone (CT.S) had significantly the highest mean AFB1 contamination (p < 0.05). Meanwhile, OTA was encountered only in CT.S zone. Furthermore, commercial samples showed higher OTA and ZEA mean concentrations than farmers samples (p < 0.05). As regards emerging mycotoxins, Fusarium mycotoxins including beauvericin (BEA), equisetin (EQUS), monoacetoxyscirpenol (MAS) and diacetoxyscirpenol (DAS) were detected in 43.2%, 43.2%, 11.4% and 10.5% of positive samples, respectively. Furthermore, 12.7%, 50.9%, 53.2% and 14.1% of grains were contaminated with Alternaria mycotoxins namely alternariol (AOH), alternariolmonomethyl ether (AME), tentoxin (TEN) and tenuazonic acid (TA), respectively. The majority of emerging Fusarium and Alternaria mycotoxins mean levels were significantly higher in grains from north coastal area (p < 0.01). The present study highlighted a wide range of mycotoxins in Tunisian pearl millet with a different mycotoxin patterns within the agroecological zones.

The actinobacteria Streptomyces sp. AV05 appears to be a potential biocontrol agent (BCA) against mycotoxigenic fungi. It was found to significantly inhibit F. verticillioides growth and mycotoxin production during their co-cultivation. F. verticillioides growth was durably affected while the decrease of the toxin production levels was reversible, suggesting different BCA actions. The study of both transcriptomes brought useful information on the microbial interaction. RNA-seq data indicated that the dual interaction modified genetic expression of both microorganisms as 18.5 % of the genes were differentially expressed for the fungus against 3.8 % for the actinobacteria. Fungal differentially expressed genes (DEGs) were equally up and down regulated while bacterial ones were mainly upregulated. We especially focused the analysis of DEGs on fungal defense reaction to bacterial attack. For example, if this potential BCA implements a strategy of antibiosis with the over expression of 'siderophore-interacting protein' linked to the production of bacteriocins, the fungus in a state of stress is able to adapt its metabolism by up-regulation of amidase. It could correspond to the induction of resistance gene clusters and suggest a detoxification process. Moreover fumonisins-related pathway appears underexpressed in the presence of Streptomyces that explain the reduction of fumonisin accumulation observed.

Phytopathogenic and/or mycotoxigenic filamentous fungi are involved in a great number of plant diseases that cause yield and quality losses of crops. Besides the economic damages, these fungi produce mycotoxins that present health risks for humans and animals who consume contaminated foods. The most dangerous mycotoxins in the agriculture and the food industry that are regulated in European Union (trichothecenes especially deoxynivalenol, fumonisins, aflatoxins and ochratoxin A) are produced by three main fungal genera ( Fusarium, Aspergillus and Penicillium ). Many approaches have been applied to prevent and manage the phytopathogenic and/or mycotoxigenic fungi. However, these methods involve the use of chemical inputs that are harmful for humans, animals and environment. In a concern of sustainable development, the application of biocontrol has been considered for addressing this problem in a more environmentally friendly way. This review considered the incidence of the three fungal genera and their mycotoxins in crops and in foodstuff. The impacts of the fungal contamination and the toxin accumulation were reported. Besides, the biological control means against these pathogens were reviewed. Among them, organic amendments showed to be effective in both producing antifungal activities and reinforcing plant health.

The effects of light at different wavelengths and photoperiod on growth and ochratoxin A production of Aspergillus carbonarius and Aspergillus westerdijkiae were studied: far-red (740 nm), red (625 nm), blue (445 nm), and UV-A (366 nm). Fungal growth was not significantly affected by photoperiod or light wavelength; the only exception was A. westerdijkiae which showed reduced growth under UV-A light (366 nm). Short-wavelength blue light (445 nm) and UV-A light caused a reduction in ochratoxin A production of both fungal species. However, long-wavelength red light (625 nm) and far-red light (740 nm) reduced ochratoxin A production only in A. westerdijkiae but not in A. carbonarius. It is believed that this difference in reactivity to light is due to differences in the melanin content of the two fungal species: A. carbonarius is a black fungus with higher melanin content than A. westerdijkiae, a yellow fungus. Other possible explanations for the reduction of ochratoxin A production by light were also discussed.

Ochratoxin A (OTA) is a nephrotoxic, teratogenic, immunotoxic, and carcinogenic mycotoxin which is produced in tropical zones mainly by Aspergillus carbonarius, A. niger, A. ochraceus, and A. westerdijkiae. A. ochraceus and A. westerdijkiae species are phenotypically and genomically very close but A. westerdijkiae produce OTA at a very higher level than A. ochraceus. These species have been differentiated recently. The DNA primer pairs which were drawn so far are not specific and a genomic region of the same size is amplified for both species or they are too specific, and in this case, the DNA of a single species is amplified. To help preventing OTA contamination of foodstuffs, the PCR‐DGGE (Denaturing Gradient Gel Electrophoresis) method was used to discriminate between A. ochraceus and A. westerdijkiae DNA fragments of the same size but with different sequences and thus faster access to a diagnosis of the toxigenic potential of the fungal microflora. The proposed methodology was able to differentiate A. westerdijkiae from A. ochraceus with only one primer pairs in a single run. A calibration based on initial DNA content was obtained from image analysis of the DGGE gels and a method of quantification of the two strains was proposed.

The prevalence of diarrheal diseases in children aged from 6 to 24 months in Burkina Faso is 38%. These diarrheas may be due to the consumption of contaminated weaning food. Therefore, the microbiological quality of follow up infant flours used as supplement foods is a key-point to reduce children diseases. In this study, the microbiological safety of locally-produced infant flours was investigated. One hundred and ninety-nine (199) samples were collected mainly in retails outlets and in Recovery and Nutrition Education Centers. According to the Burkina Faso regulations, microbiological analyses were carried out for Total Aerobic Mesophilic Flora (TAMF), thermotolerant coliforms, Salmonella spp. and yeasts/molds. The bacterial and fungal isolates were identified using phenotypic and genotypic methods and the study of the production of mycotoxins was carried out from the fungal isolates. In collected samples, the TAMF count ranged from 0 to 1.8 × 106 CFU/g with a total average of 6.3 × 104 CFU/g. About 2% of the samples had a microbial load exceeding the standards (105 CFU/g). No Salmonella spp. was isolated in the final infant flours. However, the presence of Enterobacteriaceae (Klebsiella spp. Enterobacter spp. and Cronobacter spp.) was detected and molecular characterization revealed also the presence of fungal species of the genus Aspergillus spp., Penicillium spp. and Fusarium spp. Some of these species were found to produce aflatoxins, ochratoxin A and fumonisins, which are potential carcinogenic toxins. These results demonstrated the need for a preventive approach based on the application of Hazard Analysis Critical Control Point in the food industry to ensure food safety of infant flours in Burkina Faso.

Introduction Ochratoxin A (OTA) is a toxic secondary metabolite produced by fungi of the genera Aspergillus and Penicillium. It has been shown to have carcinogenic and immunotoxic properties in rats and to be responsible for human and animal kidney pathologies. OTA content in coffee was shown to be closely link to harvesting conditions, postharvest processing conditions and especially dry processing, storage and transportation conditions. Purpose Fairly little is known about the conditions for contamination by fungi responsible for OTA production, their propagation and conditions for OTA production. Biodiversity and dynamics of fungal populations linked to OTA production could be studied by PCR-DGGE genetic fingerprinting with the aim to understand the effects of postharvest processing on the microbiota. Results DGGE fingerprints analyzed by multivariate analysis showed an evolution of the fungal microflora of coffee during the different stages of the postharvest treatments (wet and dry processes) by extraction and amplification of 26S (yeasts) and 28S rDNA (filamentous fungi). PCR-DGGE stages were optimized: extraction and amplification, repeatability and sensitivity methodology applied to fungi were tested. Conclusion PCR-DGGE is a rapid molecular technique to monitor the dynamics of coffee microbial populations (fungi and yeast). Significance of study PCR-DGGE is a promising tool in order to investigate OTA production in coffee beans.

Dracaena cochinchinensis Lour. is an ethnomedicinally important plant used in traditional Chinese medicine known as dragon’s blood. Excessive utilization of the plant for extraction of dragon’s blood had resulted in the destruction of the important niche. During a study to provide a sustainable way of utilizing the resources, the endophytic Actinobacteria associated with the plant were explored for potential utilization of their medicinal properties. Three hundred and four endophytic Actinobacteria belonging to the genera Streptomyces, Nocardiopsis, Brevibacterium, Microbacterium, Tsukamurella, Arthrobacter, Brachybacterium, Nocardia, Rhodococcus, Kocuria, Nocardioides, and Pseudonocardia were isolated from different tissues of D. cochinchinensis Lour. Of these, 17 strains having antimicrobial and anthracyclines-producing activities were further selected for screening of antifungal and cytotoxic activities against two human cancer cell lines, MCF-7 and Hep G2. Ten of these selected endophytic Actinobacteria showed antifungal activities against at least one of the fungal pathogens, of which three strains exhibited cytotoxic activities with IC50-values ranging between 3 and 33 μg·mL−1. Frequencies for the presence of biosynthetic genes, polyketide synthase- (PKS-) I, PKS-II, and nonribosomal peptide synthetase (NRPS) among these 17 selected bioactive Actinobacteria were 29.4%, 70.6%, and 23.5%, respectively. The results indicated that the medicinal plant D. cochinchinensis Lour. is a good niche of biologically important metabolites-producing Actinobacteria.

Ochratoxin A (OTA) is a mycotoxin that contaminates several foodstuffs, including cocoa. It has nephrotoxic, teratogenic and carcinogenic properties in humans. The effect of post-harvest processing and storage on the OTA contamination of cocoa was studied over three successive cocoa seasons (2005, 2006 and 2007) in Cameroon. The type of fermentation (box or heap) did not significantly influence bean OTA content, which varied from undetectable (

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.

International audience; A method was developed to analyze neutral lipids through the use of three triglycerides, four free fatty acids, six di- and four mono-glycerides standards by high performance liquid chromatography (HPLC) normal phase coupled with either with evaporative light scattering detector (ELSD) or with mass spectrometry (MS) operating in atmospheric pressure chemical ionization (APCI) mode. The method was applied to the determination of the neutral lipid fraction from a Botryococcus braunii race A (B. braunii) culture. This method led us to identify neutral lipids synthesized by B. braunii in a single analysis within 45min through HPLC-APCI-MS/MS technique.

Jerusalem artichoke is a favorable substrate for inulin or fructose syrup production. The sugar content and the fructose ratio of inulin depend on various factors, particularly on the date of harvest. Incomplete fermentation of extracts by selected yeasts allows the production of inulin with increased fructose content. The yeast strains (Saccharomyces cerevisiae, S. diastaticus...) are chosen for their ability to ferment sucrose and inulin small polymers, but not easily inulin large polymers. A good increase in the fructose ratio and a good yield in residual sugars can be obtained with the better strains. After fermentation and acid or enzymatic hydrolysis, extracts from “early” and “late” harvested tubers lead to syrups of good quality containing up to 95% and 90% of fructose respectively. This fermentative enrichment process is competitive with others (for example, chromatographic enrichment), is appropriate to raw extracts, simplifies the purification steps, and also permits the simultaneous benefit of production of by-products in the form of ethanol and yeast (in addition to the pulps). Unhydrolyzed inulin polymers with high fructose content can be recovered by this selective fermentation.

Ochratoxin-A (OTA) is a mycotoxin that has nephrotoxic, tetragenic, immunotoxic and carcinogenic effects in the human organism. It contaminates several foodstuffs, notably cocoa. The purpose of our study was to compare the incidence of cocoa pod integrity on the fungal microflora and ochratoxin- A production in Cameroon. Irrespective of pod condition, fermented cocoa beans were contaminated by OTA. The maximum mould content was obtained in beans from damaged pod. However, the fungal microflora was more diversified for beans from pod damaged during harvesting than for beans from intact pods, throughout the post-harvest process. The toxigenic strains isolated belonged to the genera Aspergillus. Aspergillus carbonarius isolated from damaged pods, displayed the greatest OTA production which was 110.7 ng.g-1 on cocoa medium and 2772,0 ng.g-1 on official medium. There was a good correlation between OTA presence in the beans and isolated toxigenic strains.

The sucrose hydrolysis activity of dense spherical yeast flocs, cultivated on a sucrose medium in a continuous reactor with internal settler, is nearly proportional to the particle surface. From computer simulation, in good agreement with experimental determinations, the calculated sucrose penetration depth is in the range 0.2–0.3 mm, a dimension smaller than the usual diameter of strongly flocculating yeast particles. From specific gravity determinations, the flocs can be considered as homogeneous and cannot exhibit a fractal structure, reported in the literature for a number of microbial aggregates. However, the analysis of the sucrose hydrolysis rates reveals that the cell density may be lower in the outer layer of the flocs. © 1992 John Wiley & Sons, Inc.

At high flow rates, the continuous alcoholic fermentation of sucrose in a laboratory fermenter with internal cell recycle, using a strongly flocculating yeast can be limited by the substrate hydrolysis. This system is sensitive to glucose catabolic repression and to mineral deficiency. The release of invertase activity in the medium is negligible. From theoretical and experimental considerations, the hydrolysis rate is imposed by diffusionnal limitations in the biomass particles. Nevertheless, ethanol productivities as high as 68 g/L.h can be reached, without biomass retention problems. A better understanding of the basic phenomena involved in floc formation and evolution is required to control reactor performances.

The diffusion of small molecules (sugars and alcohols) through a dense layer of flocculating yeast has been studied and compared to the theorical value calculated from parameters such as porosity and yeast density. Lactose, ethanol and methanol were chosen as model molecules. In comparison with water, the diffusion rate of lactose is divided by three. Alcohols which cross the cell envelope diffuse relatively faster than lactose which was assumed not to penetrate the cells. An increase of the lactose diffusion rate is observed when the yeast are heat killed.

Ochratoxin A (OTA) is the main mycotoxin occurring in cocoa. A study was conducted in Cameroon to assess how filamentous fungi and toxigenesis were affected by the type of cocoa post-harvest treatment (boxes or heaps). The filamentous fungi isolated were almost identical when fermentation was carried out in boxes or heaps, with the presence of abundant black Aspergillus filamentous fungi: A. niger and A. carbonarius. Filamentous fungi were more abundant at the end of the harvesting season. Factors affecting bean integrity (poor handling, deferred processing) resulted in a qualitative and quantitative increase in contamination, when the total number of filamentous fungi could reach a maximum value of 5.5+/-1.4x10(7) CFU g(-1) and black Aspergilli a maximum value of 1.42+/-2.2x10(7) CFU g(-1). A toxigenesis study showed that Aspergillus carbonarius was the main OTA-producing strain isolated. Its maximum production could reach 2.77 microg g(-1) on rice medium. Aspergillus niger strains did not always produce OTA and their toxigenesis was much lower. Fermented dried cocoa from poor quality pods was the most contaminated by OTA: up to 48 ng g(-1).