Glucose reaction with fumonisin B1 partially reduces its toxicity in swine

Ochratoxin A and its reaction products affected by sugars during heat processing

Ochratoxin A (OTA) is a nephrotoxin produced by many species in two fungal genera of Aspergillus and Penicillium under virtually all agricultural environments. Hence, OTA occurs frequently in agricultural commodities and their downstream products worldwide. In this study, thermal stability of OTA in the presence of sugars commonly added to food products including glucose, fructose, and sucrose was investigated by analyzing their reaction products with HPLC-FLD and LC-MS/MS. Samples were heated at three different temperatures (100, 125, and 150 °C) in 10-min intervals for up to 60 min in the absence of food matrix. Analysis showed increased OTα and OTα-amide and decreased OTA isomer (14-R-OTA) formation when OTA was heated with sugars. Among the sugars tested, adding fructose resulted in significantly lower OTA levels than glucose, sucrose, or no sugar added control. Addition of fructose also shifted OTA degradation product profile to less toxic OTα-amide, instead of OTA isomer which has similar toxicity to OTA. These results suggest that added sugars influenced the levels of OTA and its degradation products formed during thermal processing, and may provide a means to reduce the toxicity of OTA in food.

Hydrolysed fumonisin B1 and N-(deoxy-D-fructos-1-yl)-fumonisin B1: stability and catabolic fate under simulated human gastrointestinal conditions

Food processing may induce thermal degradation of fumonisins in corn via Maillard-type reactions, or alkaline hydrolysis via loss of the two tricarballylic acid moieties. In the former case, N-(1-deoxy-D-fructos-1-yl)-fumonisin B(1) (NDF) can be formed, while the latter derivative is called hydrolysed fumonisin B(1) (HFB(1)). The aim of this study was to deepen the knowledge about the gastrointestinal stability of HFB(1) and NDF in humans. Due to the lack of standard, NDF was chemically synthesised and cleaned up in high purity to be used for further experiments. While NDF is already partially cleaved (about 41%) during simulated digestion, it remained rather stable towards human colon microflora. In contrast to this, HFB(1) is partially metabolised by the colon microflora to unknown compounds after 24 h of fermentation, as seen by a loss of about 22%. Concluding, the cleavage of NDF during digestion as well as the likely metabolisation of HFB(1) emphasise the need for animal trials to ascertain their toxicity in vivo.

Effects of different extrusion conditions on the chemical and toxicological fate of fumonisin B1 in maize: a short review

Fumonisin B1 (FB1) is a common mycotoxin found in maize and maize-based food products. Although FB1 is relatively heat stable and survives most thermal processes, extrusion cooking has been shown to be effective at reducing levels of the toxin in contaminated maize. This review summarises studies on the chemical and toxicological fate of FB1 in maize extruded under different conditions. Overall, these studies indicate that stability of FB1 depends on the extrusion conditions, e.g. temperature and screw speed, and that the presence of reducing sugars augment apparent loss of the toxin. The chemical fate of FB1 was investigated by measuring FB1, hydrolysed FB1, and N-substituted FB1 compounds with a mass balance approach while the relative toxicity was determined by rat feeding trials. FB1 in contaminated grits was reduced by 21-37% and 77-87% in the absence and presence of 10% (w/w) glucose, respectively, during single-screw extrusion. Greater reductions of 64-72% and 89-94% were achieved by twin-screw extrusion. Mass balance analysis showed that most of the FB1 in grits extruded without glucose was recovered as FB1, whereas the FB1-glucose reaction product, N-(deoxy-D-fructos-1-yl)-fumonisin B1 was the prevalent form after extrusion with glucose. 23 to 38% of FB1 in extruded grits with and without added glucose was bound to component(s) of the maize grits. Only 37-46% of FB1 present in unextruded grits could be recovered as one of the fumonisin species (hydrolysed FB1, N-substituted FB1 compounds) or as matrix-bound forms in extruded grits. Reduced FB1 concentrations in extruded grits and the even lower concentrations in grits extruded with glucose resulted in a dose-dependent reduction of toxicity as shown by the less severe apoptotic lesions and sphingolipid effects that were found in the kidneys of rats. In summary, extrusion processing, especially with glucose supplementation, is potentially useful to reduce FB1 concentrations and toxicity of contaminated maize.

Masked fumonisins in processed food: co-occurrence of hidden and bound forms and their stability under digestive conditions

Fumonisins can occur in foodstuffs as free forms (prent, partially hydrolysed, or totally hydrolysed), as covalently bound fumonisins (bound fumonisins) and as non-covalently bound fumonisins (hidden fumonisins). The formation of several covalently bound fumonisin B1 conjugates upon reaction with sugars and/or amino acids has been reported in the literature so far, but occurrence data are still very poor. Since very little is known about the relevance of both hidden and bound fumonisins in processed products, the present study aimed to evaluate the occurrence of both masked forms in maize-based food products and to study their stability under digestive conditions. The behaviour of covalently bound fumonisin B1 conjugates upon in vitro digestion was evaluated, demonstrating their stability under these conditions. In addition, the co-occurrence of hidden and bound fumonisins in maize-based food products was investigated by application of both alkaline hydrolysis and simulated in vitro digestion assay. The experiments clearly showed that bound fumonisins were rather stable under the applied conditions, whereas hidden fumonisins released their parent forms.

Fumonisin elimination and prospects for detoxification by enzymatic transformation

A technology to efficiently reduce the concentration of carcinogenic and toxic fumonisins in food and feed would be desirable. This class of mycotoxins is produced by the maize pathogen Fusarium verticillioides and other fungi. Fumonisins are frequently found in maize from the warm growing regions of the world, sometimes in considerable concentrations. Their molecular similarity with sphingolipids enables their binding to mammalian ceramide synthase, and the resulting interference with sphingolipid metabolism. Recently, we reported on a cluster of genes of Sphingopyxis sp. MTA144 which enables this alphaproteobacterium to degrade fumonisins. These and the previously known fumonisin catabolism genes and enzymes from the black yeast Exophiala spinifera and from bacterium ATCC 55552 allow the consideration of prospects for enzymatic detoxification of fumonisins in food and feed. All the known fumonisin catabolism pathways start by hydrolytic release of the two tricarballylic acid side chains, followed by removal of the 2-amino group from the core chain by different enzymatic mechanisms. The potential for application of feed enzymes for fumonisin detoxification in the gastrointestinal tract of animals is discussed, and possible applications in processing of maize for feed or food are also considered. To be able to evaluate the requirement for, and potential of, a new, enzyme-based fumonisin detoxification technology, an overview of the state of the art of fumonisin elimination and the known chemical reactions of fumonisins in processing or decontamination is also given. There is a special focus on the toxicity of hydrolysed fumonisins, because they can be generated from fumonisins both by an established, traditional method of maize processing, nixtamalisation, and by enzymatic biotransformation. As a complement to other approaches, enzymatic degradation of fumonisins to ameliorate the health risk of contaminated maize for animals, and possibly also for humans, seems feasible.

Enzyme characteristics of aminotransferase FumI of Sphingopyxis sp. MTA144 for deamination of hydrolyzed fumonisin B₁

Fumonisins are carcinogenic mycotoxins that are frequently found as natural contaminants in maize from warm climate regions around the world. The aminotransferase FumI is encoded as part of a gene cluster of Sphingopyxis sp. MTA144, which enables this bacterial strain to degrade fumonisin B(1) and related fumonisins. FumI catalyzes the deamination of the first intermediate of the catabolic pathway, hydrolyzed fumonisin B(1). We used a preparation of purified, His-tagged FumI, produced recombinantly in Escherichia coli in soluble form, for enzyme characterization. The structure of the reaction product was studied by NMR and identified as 2-keto hydrolyzed fumonisin B(1). Pyruvate was found to be the preferred co-substrate and amino group receptor (K (M) = 490 μM at 10 μM hydrolyzed fumonisin B(1)) of FumI, but other α-keto acids were also accepted as co-substrates. Addition of the co-enzyme pyridoxal phosphate to the enzyme preparation enhanced activity, and saturation was already reached at the lowest tested concentration of 10 μM. The enzyme showed activity in the range of pH 6 to 10 with an optimum at pH 8.5, and in the range of 6°C to 50°C with an optimum at 35°C. The aminotransferase worked best at low salt concentration. FumI activity could be recovered after preincubation at pH 4.0 or higher, but not lower. The aminotransferase was denatured after preincubation at 60°C for 1 h, and the residual activity was also reduced after preincubation at lower temperatures. At optimum conditions, the kinetic parameters K (M) = 1.1 μM and k (cat) = 104/min were determined with 5 mM pyruvate as co-substrate. Based on the enzyme characteristics, a technological application of FumI, in combination with the fumonisin carboxylesterase FumD for hydrolysis of fumonisins, for deamination and detoxification of hydrolyzed fumonisins seems possible, if the enzyme properties are considered.

Degradation of fumonisin B1 by the consecutive action of two bacterial enzymes

Detoxification of the mycotoxin fumonisin B(1) comprises at least two enzymatic steps, an initial deesterification reaction, followed by deamination of the resulting hydrolyzed fumonisin B(1). In this study, two genes that are responsible for degradation of fumonisin B(1) by the bacterium Sphingopyxis sp. MTA144 were identified within a gene cluster, assumed to be associated with fumonisin degradation. The first gene encodes a protein which shows similarity to carboxylesterases, type B. The second gene encodes a polypeptide homologous to aminotransferases, class III. The two genes were isolated and expressed heterologously. The effect of the recombinant enzymes on fumonisin B(1) and hydrolyzed fumonisin B(1) was determined. The recombinant carboxylesterase was shown to catalyze the deesterification of fumonisin B(1) to hydrolyzed fumonisin B(1). The heterologously expressed aminotransferase was shown to deaminate hydrolyzed fumonisin B(1) in the presence of pyruvate and pyridoxal phosphate. We propose that the consecutive action of these two enzymes is sufficient for fumonisin B(1) detoxification. The results of this work provide a basis for the development of an enzymatic detoxification process for fumonisin B(1) in food and animal feed, especially under oxygen limited conditions, as they are found, e.g. in ensilaged forage or in the intestinal tract of animals.

Fumonisin B-glucose reaction products are less toxic when fed to swine

The effects of fumonisin B-glucose reaction products in swine diets was examined. Pigs were fed diets containing 528 micromol of total fumonisin B/kg (FB), 528 micromol of total FB-glucose adducts/kg (FB-G, 122 micromol of unreacted FB/kg), or 0 micromol of total FB/kg for 15 days to test the efficacy of the FB-G reaction products in detoxifying FB. Weight gain in FB pigs was lower than in FB-G or controls, which was correlated with feed intake reduction in FB pigs. Serum aspartate aminotransferase, gamma-glutamyltransferase, and total bilirubin in FB pigs were higher than in FB-G or control pigs. Serum sphinganine/shingosine ratios in FB pigs were higher than in FB-G or control pigs. Microscopic examination of tissues from FB pigs showed generalized liver necrosis and apoptosis with marked cellular pleomorphism and disorganized hepatic cords. The liver and kidneys in the FB-G group appeared to be normal. Tissues of controls were free of lesions. Results suggest that dietary FB-G products are less toxic to swine and may provide an detoxification approach in instances of widespread FB grain contamination (p < 0.05).