Simple intervention method to reduce fumonisin exposure in a subsistence maize-farming community in South Africa

In the Centane magisterial area of South Africa, high rates of oesophageal cancer have been associated with home-grown maize contaminated with fumonisins. The aim of this study was to implement a simple intervention method to reduce fumonisin exposure in a subsistence-farming community. The hand-sorting and washing procedures, based on traditional maize-based food preparation practices, were previously customised under laboratory-controlled conditions. Home-grown maize and maize-based porridge collected at baseline were analysed for fumonisin B₁, B₂ and B₃. The geometric mean (95% confidence interval) of fumonisin contamination in the home-grown maize at baseline was 1.67 (1.21–2.32) mg kg^?1 and 1.24 (0.75–2.04) mg kg ^?1 (dry weight) in the porridge. Fumonisin exposure was based on individual stiff porridge consumption and the specific fumonisin levels in the porridge (dry weight) consumed. Porridge (dry weight) consumption at baseline was 0.34 kg day^?1 and fumonisin exposure was 6.73 (3.90–11.6) µg kg^?1 body weight day^?1. Female participants (n = 22) were trained to recognise and remove visibly infected/damaged kernels and to wash the remaining maize kernels. The discarded kernels represented 3.9% by weight and the fumonisins varied from 17.1 to 76.9 mg kg^?1. The customised hand-sorting and washing procedures reduced fumonisin contamination in the maize and porridge by 84 and 65%, respectively. The intervention reduced fumonisin exposure by 62% to 2.55 (1.94–3.35) µg kg^?1 body weight day^?1. This simple intervention method has the potential to improve food safety and health in subsistence-farming communities consuming fumonisin-contaminated maize as their staple diet.     

Fusaria and fumonisins in maize from Ghana and their co-occurrence with aflatoxins

Fifteen maize samples from four markets and processing sites in Accra, Ghana were analysed for fumonisins B1, B2, and B3. All samples contained fumonisins. Total fumonisin levels for 14 samples ranged from 70 to 4222 microg kg(-1). One sample of visibly mouldy kernels contained 52 670 microg kg(-1) total fumonisins. Mycological examination of the samples showed Aspergillus spp. as the most dominant fungi (76.4%) followed by Penicillium spp. (19.9%). Fusarium formed 2.6% with Fusarium verticillioides as the predominant Fusarium species. Thirty-two Fusarium strains representing five species isolated from the maize samples were tested for the production of fumonisins in maize substrates. From 95% (21 of 22) of the F. verticillioides strains tested, all three types of fumonisins were produced. Total fumonisin levels ranged from 127 to 11 052 microg g(-1). Additional studies on maize samples from 15 processing sites in Accra revealed a co-occurrence of both fumonisins and aflatoxins in 53% (8 of 15) of the samples.     

Wheat kernel black point and fumonisin contamination by Fusarium proliferatum

Fusarium proliferatum is a major cause of maize ear rot and fumonisin contamination and also can cause wheat kernel black point disease. The primary objective of this study was to determine whether nine F. proliferatum strains from wheat from Nepal can cause black point and fumonisin contamination in wheat kernels. For comparison, the study included three Fusarium strains from US maize. In test 1, all the strains but one produced significant symptoms of kernel black point; two strains decreased kernel yield; and four strains contaminated kernels with fumonisins B₁, B₂ and B₃ as determined by liquid chromatography-mass spectroscopy. Strain Ggm202 from Nepal, which produced the highest levels of fumonisins (mean = 49 µg g^-1) on five wheat cultivars in test 1, was confirmed to produce fumonisins (mean = 38 µg g^-1) on two cultivars in test 2. The data indicate a potential for fumonisin contamination of wheat infected with F. proliferatum.     

Factors associated with fumonisin contamination of maize in Uganda

BACKGROUND: During production and handling, maize is attacked by many Fusarium species, some of which are prolific producers of fumonisins. Contamination of maize with fumonisins is influenced by climate, agronomic and postharvest practices. This study investigated the factors associated with the occurrence of fumonisins in maize produced in three agroecological zones of Uganda. RESULTS: All the maize samples were positive for fumonisins with levels ranging from 0.27 to 10 mg kg^?1. A positive and significant correlation (P < 0.01) was observed between fumonisin levels and agroecological zone. Maize from high altitude zone had significantly higher (P < 0.05) mean total fumonisin content (4.93 mg kg^?1) than maize from the mid altitude‐moist (4.53 mg kg^?1) and mid altitude‐dry (4.50 mg kg^?1) zones. Five farmer practices, namely intercropping, crop rotation, delayed harvesting, drying maize on bare ground and planting treated seeds were significantly associated with fumonisin production in maize. Intercropping, delayed harvesting and drying maize on bare ground increased fumonisin contamination whereas crop rotation and planting treated seeds reduced the contamination. CONCLUSION: All maize samples obtained from the three agroecological zones were contaminated with fumonisins. The study showed that some of the farmers' practices predispose maize to fumonisin contamination. The findings are important for future studies aimed at designing strategies to control and prevent contamination of maize with fumonisins. Copyright © 2009 Society of Chemical Industry     

Fumonisin contamination of maize in Burkina Faso, West Africa.

Maize throughout the world is frequently contaminated with a family of mycotoxins, the fumonisins, produced by species of Fusaria. The study investigated the level of fumonisin contamination of maize samples from village farms and large market traders in Burkina Faso, West Africa. Maize samples (5 kg) from each of five to six large storage barns from farms in five villages in the district of N'Dorola, Kénédougou province, western Burkina Faso, were sampled (n = 26) in Jan 1999 (> 1 year storage), and a further 26 maize samples from the same farms were collected directly from the field in October 1999. In addition, 72 maize samples were obtained in July 1999 from large markets in Bobo Dioulasso. Fumonisins were extracted from dried maize, derivatized with o-phthaldialdehyde and quantified by reversed-phase high-performance liquid chromatography with fluorescence detection. All 26 samples from the first (mean 1170 microg kg(-1), range 110-3120 microg kg(-1)) and from the second (mean 130 microg kg(-1), range 10-450 microg kg(-1)) village collection were fumonisin positive. All 72 maize samples from the large markets were also positive for fumonisins, and had the highest levels of contamination (mean 2900 microg kg(-1), range 130-16,040 microg kg(-1)). As fumonisins were a ubiquitous contaminant of maize and given that this crop is a dietary staple in this region, chronic exposure is likely.     

Investigations on the change of fumonisin content of maize during hydrothermal treatment of maize. Analysis by means of HPLC methods and ELISA

The study was subjected to the investigation of the effects of extrusion cooking, gelatinization, and cornflaking on the stability of fumonisins in artificially contaminated maize grits, spiked with fumonisin B₁ and B₂ at levels of 2 mg/kg and 0.6 mg/kg, respectively. All the processed samples were analyzed according to the AOAC-HPLC method, and some selected samples were analyzed additionally by a commercial enzyme-linked immunosorbent assay (ELISA) and after alkaline hydrolysis. All the samples showed significant decreases of the fumonisin levels. If analyzed according to AOAC-HPLC method, cooking extrusion and gelatinization reduced fumonisin levels to approximately 30-55%, cooking the grits for flaking to approximately 20-65%, and roasting the flakes to approximately 6-35% (depending on the selected technological parameters). With ELISA the fumonisin contents were 15-50% and after alkaline hydrolysis 19-380% higher than with the AOAC-HPLC method. However, the fumonisin amount added before the technological tests could not be recovered in any of the samples.     

Fumonsin B1, B2, and B3 content of commercial unprocessed maize imported into South Africa from Argentina and the USA during 1992.

The widespread occurrence of F. moniliforme and the toxic effects of its secondary metabolites, the fumonisins B1(FB1), B2(FB2) and B3(FB3), make it imperative that fumonisin contamination of maize, a major constituent of animal feed as well as the staple diet of many populations, be closely monitored to reduce the risk of fumonisin exposure. Equine leukoencephalomalacia and porcine pulmonary oedema have been associated with the intake of feed heavily contaminated with fumonisins. In addition, high levels of fumonisins in the maize-based staple diets of certain populations have been linked to a high incidence of oesophageal cancer in the Transkei region of South Africa and in Linxian and Cixian Counties, China. Bulk shipments of maize imported into South Africa from the USA and Argentina during 1992 were sampled at the port of entry to determine fumonisin levels. Of the 79 samples from two US shipments, all were positive for fumonisins, with FB1 constituting approximately 71% of the total fumonisins with an overall mean of 2.35 micrograms/gFB1. The maximum FB1 level observed was 3.9 micrograms/g. These levels contrast with those obtained from two Argentinian bulk shipments, which also were all positive for fumonisins, but had a mean FB1 level of 0.31 microgram/g and a maximum observed level of 0.7 microgram/g FB1 measured over 47 composite samples.     

Untersuchung und Bewertung der Fumonisinkontamination von einheimischem und importiertem Getreide

Cereal varieties cultivated in Germany, such as wheat, rye, grain-maize, barley, and oats were analyzed for fumonisins, including also imported maize from Argentina. In a total of 410 wheat samples and 140 rye samples of two harvesting years (1993, 1994) and in random samples of barley and oats no fumonisins were detected at all. In german grain-maize of 1993, only low fumonisin contents (17–33 ng/g) were detected occasionally. Some grain-maize samples of the 1994 harvest contained significantly higher fumonisin amounts, partly up to the mg/kg-range, which obviously is due to the extremely high temperatures during summer. In some samples of variety tests of the country the fumonisin B₁ content amounted up to 4828 ng/g and the total fumonisin content (FB₁-FB₃) up to 7132 ng/g respectively. In 1994 a total of 317 native grain-maize samples was tested, of it 109 samples of German cultivation and 208 samples from variety tests of different federeal states. Maize samples from Baden-Württemberg, which are representative to the maize harvest of this state, had a fumonisin contamination of 14%, the mean value of the contaminated samples amounting to 206 ng/g. Of the imported maize from Argentina, all the investigated 21 samples had a fumonisin content (FB₁-FB₃) of 14–1106 ng/g, the mean fumonisin content amounting to 175 ng/g.

     

Co-occurrence of fumonisins with aflatoxins in home-stored maize for human consumption in rural villages of Tanzania

This study determined maize-user practices that influence the presence of fumonisin and aflatoxin contamination of maize in food consumed in the rural areas of Tanzania. Samples of the 2005 maize harvest in Tanzania were collected from 120 households and examined for fumonisins and aflatoxins. Information on whether the maize was sorted to remove defective (visibly damaged or mouldy) maize before storage and whether the damaged and mouldy maize or the non-dehulled maize was used as food was also collected. In addition, the percentage of defective kernels in the samples was determined. Ninety per cent of the households sorted out defective maize, 45% consumed the defective maize and 30% consumed non-dehulled maize. In 52% of the samples fumonisins were determined at levels up to 11,048 µg kg^?1 (median = 363 µg kg^?1) and in 15% exceeded 1000 µg kg^?1; the maximum tolerable limit (MTL) for fumonisins in maize for human consumption in other countries. Aflatoxins were detected in 18% of the samples at levels up to 158 µg kg^?1 (median = 24 µg kg^?1). Twelve per cent of the samples exceeded the Tanzanian limit for total aflatoxins (10 µg kg^?1). Aflatoxins co-occurred with fumonisins in 10% of the samples. The percentage defective kernels (mean = 22%) correlated positively (r = 0.39) with the fumonisin levels. Tanzanians are at a risk of exposure to fumonisins and aflatoxins in maize. There is a need for further research on fumonisin and aflatoxin exposure in Tanzania to develop appropriate control strategies.     

Natural occurrence of Fusarium species, fumonisin production by toxigenic strains, and concentrations of fumonisins B1, and B2 in conventional and organic maize grown in Spain

Sixty samples of corn from both conventional and organic farms were tested for internal fungal contamination. Molds were identified to genus, and those belonging to the genus Fusarium were identified to species. Twenty isolates of Fusarium verticillioides were tested with a high-performance liquid chromatography-naphthalene dicarboxaldehyde-fluorescence method for their ability to produce fumonisins B1 and B2. The internal fungal infection in organic maize (63.20%) was significantly higher than that in conventional maize (40.27%) (P < 0.05). However, the distribution of fungal genera indicated a significantly higher prevalence of Fusarium in conventional (34.93%) than in organic (18.15%) maize, making Fusarium the predominant fungus in conventional maize. This difference in mold distribution between organic and conventional maize was attributed to the difference in cultivation system. The dominant Fusarium species in both conventional and organic samples was F. verticillioides. There were no significant differences in the ability of 20 selected isolates of F. verticillioides to produce fumonisins on conventional or organic corn. Up to 13.3% of the conventional corn samples contained fumonisins B1 and B2 at mean concentrations of 43 and 22 ng/g, respectively. Organic corn samples had somewhat lower levels of contamination: 35 ng/g fumonisin B1 and 19 ng/g fumonisin B2 (P > 0.05). The organic farming system, with well-balanced crop rotation, tillage, and compost fertilization, produced corn that was less likely to be contaminated with Fusarium species, although no significant difference in fumonisin concentrations was found between the two types of contaminated corn.     

Fate of aflatoxins and fumonisins during the processing of maize into food products in Benin

The fate of aflatoxins and fumonisins, two mycotoxins that cooccur in maize, was studied through the traditional processing of naturally contaminated maize in mawe, makume, ogi, akassa, and owo, maize-based foods common in Benin, West Africa. Levels of total aflatoxin and fumonisin were measured at the main unit operations of processing, and the unit operations that induce significant reduction of mycotoxin level were identified. Overall reduction of mycotoxin level was more significant during the preparation of makume (93% reduction of aflatoxins, 87% reduction of fumonisins) and akassa (92% reduction of aflatoxins, 50% reduction of fumonisins) than that of owo (40% reduction of aflatoxins, 48% reduction of fumonisins). Sorting, winnowing, washing, crushing combined with dehulling of maize grains were the unit operations that appeared very effective in achieving significant mycotoxin removal. Aflatoxins and fumonisins were significantly recovered in discarded mouldy and damaged grains and in washing water. Fermentation and cooking showed little effect. During the preparation of ogi and akassa, reduction of fumonisin levels measured in food matrix was lower (50%) compared to mawe and makume, probably due to significant fumonisin release in ogi supernatant. Consequently, the use of ogi supernatant for preparing beverages or traditional herbal medicines could be harmful as it is likely to be contaminated with mycotoxin from the raw maize.     

Occurrence of the C-series fumonisins in maize from the former Transkei region of South Africa

Fumonisins are a group of structurally related mycotoxins produced mainly in maize by Fusarium verticillioides and F. proliferatum. The most abundant naturally occurring analogue is fumonisin B(1) (FB(1)), with lesser amounts of fumonisin B(2) (FB(2)) and fumonisin B(3) (FB(3)) occurring. The C-series fumonisins (FCs) are structurally analogous to the B-series but lack the C-1 methyl group. Good and mouldy subsistence-grown maize samples were collected from the Centane and Bizana districts in the former Transkei region of South Africa. After extraction with methanol/water and clean-up on strong anion exchange solid phase extraction cartridges, FB(1), FB(2), FB(3), FC(1), FC(3) and FC(4) were determined by reversed-phase LC-MS/MS using positive ion electrospray ionisation. FB(1) levels in both good and mouldy maize from Centane (means (±SD) 2.75 ± 2.24 and 23.4 ± 12.5 mg kg(-1), respectively) were higher than the corresponding levels in maize samples from Bizana (means 0.056 ± 0.157 and 3.71 ± 5.01 mg kg(-1), respectively). Similarly, FC(1) levels in both good and mouldy maize from Centane (means 0.107 ± 0.099 and 0.814 ± 0.391 mg kg(-1), respectively) were higher than in Bizana, where FC(1) was detected in only one (0.018 mg kg(-1)) of 19 good maize samples and occurred in mouldy maize with a mean of 0.102 ± 0.135 mg kg(-1). A significant correlation (r=0.982, p<0.01) was observed between FB(1) and FC(1) levels in all samples, with FC(1) levels at 3.3% of the corresponding FB(1) levels. FC(4) levels were similar to FC(1), whereas only low amounts of FC(3) were detected.     

Sensitive enzyme‐linked immunosorbent assay and rapid one‐step immunochromatographic strip for fumonisin B1 in grain‐based food and feed samples

BACKGROUND: Maize contaminated with mycotoxin fumonisin B1 poses a global threat to agricultural production. In this study, polyclonal antibodies (pAb) specific to fumonisin B1 were generated from rabbits immunised with fumonisin B1–keyhole limpet haemocyanin (KLH). These antibodies were used to establish a sensitive competitive direct enzyme‐linked immunosorbent assay (cdELISA) and gold nanoparticle immunochromatographic strip for detecting fumonisin B1 levels in maize‐based foods and feeds. RESULTS: In cdELISA, fumonisins B1, B2 and B3 at concentrations of 0.42, 0.58 and 81.5 ng mL^?1 respectively caused 50% inhibition (IC₅₀) of binding of fumonisin B1–horseradish peroxidase (HRP) to the antibodies. Effective on‐site detection of fumonisin B1 was achieved by developing a rapid and sensitive pAb‐based gold nanoparticle immunochromatographic strip. This strip had a detection limit of 5 ng mL^?1 for fumonisin B1 in maize‐based samples. Additionally, the whole analytical process could be completed within 10 min. Close examination of 15 maize‐based samples by cdELISA revealed that 11 were fumonisin‐positive, with a mean concentration of 435 ± 20.1 ng g^?1. These results correlated well with those obtained by immunochromatographic strip. CONCLUSION: Both cdELISA and immunochromatographic strip methods established in this study are sensitive for rapid detection of fumonisins in agricultural commodities. Copyright © 2010 Society of Chemical Industry     

Fumonisin contamination and fumonisin producing black Aspergilli in dried vine fruits of different origin

Aspergillus niger isolates are able to produce fumonisins in high quantities on agar media with a low water activity. Several agricultural products fit this criterion, including dried vine fruits, dates and figs. Data on the occurrence and role of this species in fumonisin contamination of agricultural products with high sugar content are needed to clarify the importance of A. niger in human health. The mycobiota and fumonisin contamination of various dried vine fruit samples collected from different countries were examined to clarify the role of black Aspergilli in fumonisin contamination of such products. All except two of the examined samples were contaminated with black Aspergilli. Species assignment of the isolates was carried out using sequence analysis of part of the calmodulin gene. The range of fumonisin isomers present in the raisin samples, and produced by A. niger isolates collected from dried vine fruits was also examined using reversed-phase high-performance liquid chromatography/electrospray ionization-ion trap mass spectrometry (RP-HPLC/ESI-ITMS). Among the 30 A. niger/A. awamori isolates identified, 20 were found to be able to produce fumonisins (average contamination: 5.16 mg/kg; range: 0.017-19.6 mg/kg). The average fumonisin content of the 7 dried vine fruit samples which were found to be contaminated by potential fumonisin producing black Aspergilli was 7.22 mg/kg (range: 4.55-35.49 mg/kg). The isolates produced several fumonisin isomers also present in the dried vine fruit samples, including fumonisins B_1-4, 3-epi-FB₃, 3-epi-FB₄, iso-FB₁, and two iso-FB_2,3 forms. Fumonisin B₁ was detected for the first time in A. niger cultures. Most of these isomers have previously only been identified in Fusarium species. Our data indicate that A. niger and A. awamori are responsible for fumonisin contamination of dried vine fruits worldwide. The observed levels of contamination are alarming and pose a new threat for food safety.     

Fumonisin B(1) in maize harvested in Iran during 1999.

The fumonisin B(1) (FB(1)) contamination of maize collected in two areas of Iran during 1999 was determined. The 20 maize samples from Mazandaran Province, situated on the Caspian littoral of Iran, consisted of random samples of farmers' lots and were all contaminated with FB(1) at a mean level of 3.18 mg kg(-1) (range 0.68-7.66 mg kg(-1)). The 10 samples (of the same maize cultivar) from Isfahan Province in central Iran were purchased as maize cobs in local retail markets and had mean FB levels of 0.22 mg kg(-1) (mean of all samples, 6/10 samples positive, range <0.01-0.88 mg kg(-1)). The FB levels in Mazandaran, an area of high oesophageal cancer, were significantly (p < 0.0001) higher than the FB levels found in maize from Isfahan, an area of low oesophageal cancer in Iran.     

Effects of irradiation on fungi and fumonisin B(1) in corn, and of microwave-popping on fumonisins in popcorn.

Fumonisins are metabolites produced in corn primarily by the fungus Fusarium verticillioides (F. moniliforme) and are toxic to humans and animals. Fumonisin B(1) (FB(1)) is the primary fumonisin produced and is found frequently in corn kernels, some of which may be used as food or food ingredients. A three-part study was conducted to determine the effects of gamma- and electron beam irradiation on the levels of fumonisins in naturally contaminated field corn, and the effects of microwave-popping on fumonisins in selected, naturally contaminated popcorn. To date, no effective means have been found to reduce consistently mycotoxin levels once foods are contaminated. Aqueous solutions of FB(1) at various concentrations, samples of whole corn, and samples of ground corn containing known levels of FB(1) were irradiated with various levels of cobalt and electron beam irradiation. Popcorn samples, taken from the reject streams of popcorn processing, were popped using normal microwave-popping conditions. FB(1) in aqueous solutions was reduced by 99.7% using a minimal level of irradiation (0.5 kGray). Gamma- and electron beam irradiation did not significantly reduce levels of FB(1) in whole and ground corn. Aspergillus sp., Penicillium sp. and Fusarium sp. fungi were totally eliminated at 30 kGray in ground corn and at 100 kGray in whole corn. The normal commercial cleaning processes for microwave popcorn before packaging reduced fumonisins to <0.03 microg g(-1) for the cleaned product stream. Microwave popping of popcorn from reject streams of the cleaning operation that contained fumonisins resulted in significant reduction of the mould toxin.     

On fumonisin incidence in monoculture maize under no‐till,conventional tillage and two nitrogen fertilisation levels

BACKGROUND: Fusarium ear rot and fumonisin contamination are serious problems for maize growers. The lack of maize genotypes highly resistant to fumonisin contamination emphasises the need for management strategies to prevent contamination by this mycotoxin. There are conflicting reports regarding no‐till and nitrogen (N) fertilisation practices in relation to the incidence of fumonisins. In this study the effect of no‐till compared with conventional tillage and of N fertilisation rates on fumonisin occurrence was investigated over three years in Northern Italy. RESULTS: The average contamination of grain by fumonisins B₁ and B₂ over the three years was significantly different, with a lower value in 2000 (516 µg kg^?1) than in the other years (5846 and 3269 µg kg^?1 in 2001 and 2002 respectively). Conventional tillage and no‐till treatments had no significant effect on the incidence of fumonisins. This finding suggests that above‐ground residues infected by Fusarium would not lead to an increase in fumonisin incidence. However, N fertilisation significantly increased fumonisin levels, by 99 and 70% in 2000 and 2001 respectively. CONCLUSION: Maize monoculture does not show a cumulative effect on the occurrence of fumonisins, while high rates of N fertiliser consistently result in elevated fumonisin levels. Both these effects can be influenced by annual meteorological fluctuations. Copyright © 2008 Society of Chemical Industry     

Fumonisin production by Fusarium species isolated from cereals and feeds in Spain.

The ability of Fusarium species to produce fumonisins was studied with 145 isolates of the following species: F. moniliforme (119 isolates), F. subglutinans (12 isolates), F. proliferatum (9 isolates), F. avenaceum (1 isolate), F. oxysporum (1 isolate), and F. semitectum (3 isolates). All isolates were cultured on autoclaved corn kernels. The production of fumonisins was determined by a high-performance liquid chromatography-o-phthaldialdehyde-fluorescence method. Fumonisin production was restricted to isolates of F. moniliforme (94.1%) and F. proliferatum (100%), in the section Liseola, including all strains isolated from wheat, barley, peas, and soybean. One strain of F. proliferatum isolated from maize produced 30,949 microg/g of fumonisin B1 and 16,966 microg/g of fumonisin B2.     

Comparison of fumonisin B1 biosynthesis in maize germ and degermed kernels by Fusarium verticillioides

Fusarium verticillioides produces a group of mycotoxins known as fumonisins in maize kernels. Fumonisins are associated with a variety of mycotoxicoses in humans and animals; thus, their presence in food is a considerable safety issue. This study addressed fumonisin B1 (FB1) production in two components of the maize kernel, namely the germ tissues and the degermed kernel. Growth of F. verticillioides was similar in colonized germ tissue and degermed kernels, but FB1 production was at least five times higher in degermed maize kernels than in germ tissue. Expression of the fumonisin polyketide synthase gene, FUM1, as measured by beta-glucuronidase (GUS) and Northern blot analysis, followed the same pattern as FB1 production. Also correlated to FB1 was a concomitant drop in pH of the colonized degermed kernels. A time course experiment showed that degermed kernels inoculated with F. verticillioides became acidified over time (from pH 6.4 to 4.7 after 10 days of incubation), whereas colonized germ tissue became alkaline over the same period (from pH 6.5 to 8.5). Because conditions of acidic pH are conducive to FB1 production and alkaline pH is repressive, the observed correlation between the acidification of degermed kernels and the increase in FB1 provides one explanation for the observed differences in FB1 levels.     

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.