Evaluation of the pH effect on complex formation between bovine β-lactoglobulin and aflatoxin M1: a molecular dynamic simulation and molecular docking study

The aim of this work was to evaluate interaction between aflatoxin M1 (AFM1) and structural models of β-lactoglobulin (β-LG) at pH 4.0 and 6.5. This information would provide an explanation of the variability in AFM1 during cheese production. Once β-LG models were optimized using molecular dynamic (MD) simulation, it was found that a region of the Calyx cavity underwent conformational changes, at the E-F loop, from the closed conformation at pH 6.5 to the open at pH 4.0. No differences in Site C conformation were observed at both pH. The binding free energy (ΔGb) of the β-LG-AFM1 complexes at the different pHs were determined by molecular docking. The ΔGb values obtained for the Calyx cavity showed that at pH 4.0 there is a more stable complex formation compared to pH 6.5 with values of -42.6 and -32.0 kJ mol-1, respectively. On the contrary, in the complexes formed in Site C at both pH´s there were no differences. Likewise, the ΔGb in the dimer interface was evaluated, obtaining a value of -29.3 kJ mol-1, like those obtained at Site C. In addition, by the MD simulations of the β-LG-AFM1 complexes, it was observed that at acidic pH the binding of AFM1 with β-LG is more stable. In conclusion, the computational tools showed that the most stable complex was formed at the Calyx cavity at pH 4.0. This suggests that during cheese production using acidic coagulation, the whey proteins show higher affinity toward AFM1 which may explain the observed variability of mycotoxin.Communicated by Ramaswamy H. Sarma.

Mixtures of Mycotoxins, Phytoestrogens, and Other Secondary Metabolites in Whole-Plant Corn Silages and Total Mixed Rations of Dairy Farms in Central and Northern Mexico

Mycotoxins and endocrine disruptors such as phytoestrogens can affect cattle health, reproduction, and productivity. Most studies of mycotoxins in dairy feeds in Mexico and worldwide have been focused on a few (regulated) mycotoxins. In contrast, less known fungal toxins, phytoestrogens, and other metabolites have been neglected and underestimated. This study analyzed a broad spectrum (>800) of mycotoxins, phytoestrogens, and fungal, plant, and unspecific secondary metabolites in whole-plant corn silages (WPCSs) and total mixed rations (TMRs) collected from 19 Mexican dairy farms. A validated multi-metabolite liquid chromatography/electrospray ionization-tandem mass spectrometric (LC/ESI-MS/MS) method was used. Our results revealed 125 of >800 tested (potentially toxic) secondary metabolites. WPCSs/TMRs in Mexico presented ubiquitous contamination with mycotoxins, phytoestrogens, and other metabolites. The average number of mycotoxins per TMR was 24, ranging from 9 to 31. Fusarium-derived secondary metabolites showed the highest frequencies, concentrations, and diversity among the detected fungal compounds. The most frequently detected mycotoxins in TMRs were zearalenone (ZEN) (100%), fumonisin B1 (FB1) (84%), and deoxynivalenol (84%). Aflatoxin B1 (AFB1) and ochratoxin A (OTA), previously reported in Mexico, were not detected. All TMR samples tested positive for phytoestrogens. Among the investigated dietary ingredients, corn stover, sorghum silage, and concentrate proportions were the most correlated with levels of total mycotoxins, fumonisins (Fs), and ergot alkaloids, respectively.

Foreword – special issue Mycotoxins in Latin America

Latin America with its considerable North-South extent is subject to climate that varies from tropical, subtropical and warm temperate to temperate. Different agricultural products are produced in the area including cereals, oilseeds, beans, fruits and nuts together with animal production including cattle for beef and milk, pigs, poultry and fish. The heterogeneity of agriculture in Latin America is reflected in the diversity of the region’s farm structures. While agriculture in the Southern Cone is dominated by large, commercial and export-oriented farms, particularly in Argentina and Brazil, besides increasingly in other countries like Uruguay, much of the rest of the region is characterised by smallholder and family agriculture. The contamination of agricultural products with mycotoxins has impact both human and animal health, as well as the economy due to losses related to rejections of agricultural products and by-products during trade. The economic burden related to the consumption of mycotoxins by animals is especially important, causing productivity losses up to the death of animals. The relevant mycotoxins are fumonisins, deoxynivalenol (DON) and zearalenone (ZEN) in cereals and cereal-based products, aflatoxins in cereals, oily seeds and nuts, aflatoxin M1 in milk and dairy products as well as ochratoxin A (OTA) in coffee, grapes and raisins. Co-occurrence of mycotoxins has also been observed mainly with aflatoxins and fumonisins in different Latin American countries (Torres et al., 2015). Advances on legislation in different countries including Argentina, Brazil, Chile, Mexico and Uruguay have been done to establish maximum limits for mycotoxins including aflatoxins, DON, ZEN, OTA, patulin and ergot alkaloids (ANVISA, 2011/2017; CAA, 2019/2021, Norma Oficial Mexicana, N.-243-S., 2010/2010; Reglamento Sanitario de los Alimentos, 2013).