Evaluation of mycotoxin content in soybean (Glycine max l.) grown in Rwanda

Soybean is a critical food and nutritional security crop in Rwanda. Promoted by the Rwandan National Agricultural Research System for both adults and as an infant weaning food, soybean is grown by approximately 40% of households. Soybean may be susceptible to the growth of mycotoxin-producing moulds; however, data has been contradictory. Mycotoxin contamination is a food and feed safety issue for grains and other field crops. This study aimed to determine the extent of mycotoxin contamination in soybean, and to assess people’s awareness on mycotoxins. A farm-level survey was conducted in 2015 within three agro-ecological zones of Rwanda suitable for soybean production. Soybean samples were collected from farmers (n=300) who also completed questionnaires about pre-and post-harvest farm practices, and aflatoxin awareness. The concentration of total aflatoxin in individual soybean samples was tested by enzymelinked immunosorbent assay (ELISA) using a commercially-available kit. Other mycotoxins were analyzed using liquid chromatography-mass spectrometry (LCMS/ MS) on 10 selected sub samples. Only 7.3% of the respondents were aware of aflatoxin contamination in foods, but farmers observed good postharvest practices including harvesting the crop when the pods were dry. Using enzyme-linked immunosorbent assay (ELISA), only one sample had a concentration (11 μg/kg) above the most stringent EU maximum permitted limit of 4 μg/kg. Multi-mycotoxins liquid chromatography-mass spectrometry (LC-MS/MS) results confirmed that soybeans had low or undetectable contamination; only one sample contained 13μg/kg of sterigmatocystine. The soybean samples from Rwanda obtained acceptably low mycotoxin levels. Taken together with other studies that showed that soybean is less contaminated by mycotoxins, these results demonstrate that soybean can be promoted as a nutritious and safe food. However, there is a general need for educating farmers on mycotoxin contamination in food and feed to ensure better standards are adhered to safeguard the health of the consumers regarding these fungal secondary metabolites.Key words: soybean, safety, mould, aflatoxin, mycotoxins, sterigmatocystine, ELISA, LC-MS/MS, Rwand

Mycobiota and toxigenecity profile of Aspergillus flavus recovered from food and poultry feed mixtures in Cameroon

A total of 202 poultry feed and its raw ingredients collected from different agroecological zones of Cameroon were examined for total mycoflora and the ability of A. flavus isolates to produces aflatoxin B1. Dilution plating was used for fungal isolation. The mean fungal contamination levels were significantly higher in maize and peanut meal as compared with broiler and layer feeds. In peanut meal and poultry feed, the most representative fungi were A. flavus, A. niger, A. oryzae, F. solani, F. verticilloides, Penicillium spp, and Rhizopus spp. Of all the fungi encountered, A. flavus was encountered in 90% of white maize and 28.5% of yellow maize samples. The frequency of isolation of the most representative fungi in peanut meal, broiler and layer feed was 100, 94, and 76.5% for A. flavus and 70.6, 82.3, and 76.5% for Penicillium spp, respectively. Molecular identification using the Intergenic Spacer Gene (IGS) for aflatoxin biosynthesis confirmed all fungi identified morphologically as A. flavus. Aflatoxin B1 analysis showed that all the A. flavus isolates encountered were aflatoxin B1 producers. Conclusion from this study indicate that the use of peanut meal in poultry feed is risky, and can impact poultry health and economic benefits

Assessment of aflatoxin contamination of maize, peanut meal and poultry feed mixtures from different agroecological zones in Cameroon

Mycotoxins affect poultry production by being present in the feed and directly causing a negative impact on bird performance. Carry-over rates of mycotoxins in animal products are, in general, small (except for aflatoxins in milk and eggs) therefore representing a small source of mycotoxins for humans. Mycotoxins present directly in human food represent a much higher risk. The contamination of poultry feed by aflatoxins was determined as a first assessment of this risk in Cameroon. A total of 201 samples of maize, peanut meal, broiler and layer feeds were collected directly at poultry farms, poultry production sites and poultry feed dealers in three agroecological zones (AEZs) of Cameroon and analyzed for moisture content and aflatoxin levels. The results indicate that the mean of the moisture content of maize (14.1%) was significantly (P < 0.05) higher than all other commodities (10.0%-12.7%). Approximately 9% of maize samples were positive for aflatoxin, with concentrations overall ranging from <2 to 42 ?g/kg. Most of the samples of peanut meal (100%), broiler (93.3%) and layer feeds (83.0%) were positive with concentrations of positive samples ranging from 39 to 950 ?g/kg for peanut meal, 2 to 52 ?g/kg for broiler feed and 2 to 23 ?g/kg for layer feed. The aflatoxin content of layer feed did not vary by AEZ, while the highest (16.8 ?g/kg) and the lowest (8.2 ?g/kg) aflatoxin content of broiler feed were respectively recorded in Western High Plateau and in Rainforest agroecological zones. These results suggest that peanut meal is likely to be a high risk feed, and further investigation is needed to guide promotion of safe feeds for poultry in Cameroon

An improved simulation model to predict pre-harvest aflatoxin risk in maize

Aflatoxin is a potent carcinogen produced by Aspergillus flavus, which frequently contaminates maize (Zea mays L.) in the field between 40° north and 40° south latitudes. A mechanistic model to predict risk of pre-harvest contamination could assist in management of this very harmful mycotoxin. In this study we describe an aflatoxin risk prediction model which is integrated with the Agricultural Production Systems Simulator (APSIM) modelling framework. The model computes a temperature function for A. flavus growth and aflatoxin production using a set of three cardinal temperatures determined in the laboratory using culture medium and intact grains. These cardinal temperatures were 11.5 °C as base, 32.5 °C as optimum and 42.5 °C as maximum. The model used a low (≤0.2) crop water supply to demand ratio—an index of drought during the grain filling stage to simulate maize crop's susceptibility to A. flavus growth and aflatoxin production. When this low threshold of the index was reached the model converted the temperature function into an aflatoxin risk index (ARI) to represent the risk of aflatoxin contamination. The model was applied to simulate ARI for two commercial maize hybrids, H513 and H614D, grown in five multi-location field trials in Kenya using site specific agronomy, weather and soil parameters. The observed mean aflatoxin contamination in these trials varied from <1 to 7143 ppb. ARI simulated by the model explained 99% of the variation (p ≤ 0.001) in a linear relationship with the mean observed aflatoxin contamination. The strong relationship between ARI and aflatoxin contamination suggests that the model could be applied to map risk prone areas and to monitor in-season risk for genotypes and soils parameterized for APSIM

Potential of using host plant resistance, nitrogen and phosphorus fertilizers for reduction of Aspergillus flavus colonization and aflatoxin accumulation in maize in Tanzania

Aflatoxin contamination (AC) in maize, caused by the fungal pathogen Aspergillus flavus(Link), starts at pre-harvest stage. Hence, interventions that reduce entry and development of A. flavus in the field are required. Trials were carried out at Seatondale and Igeri, to evaluate the effects of nitrogen and phosphorus fertilizer combinations, hereafter referred to as fertilizers, on A. flavus and AC in maize kernels. The main treatments were four combinations of N and P fertilizers (60 or 120 kg Nha−1 with 15 or 30 kg Pha−1) and sub-treatments were of six popular maize hybrids. Plants at 50% silking were inoculated with the fungus through the silk channels. Grains from inoculated and control ears were analysed for AC using Enzyme Linked Immunosorbent Assay, and pathogen content quantified by Quantitative Polymerase Chain reaction. Higher AC (mean 6.51 μg kg−1) occurred at Seatondale than Igeri (mean 0.45 μg kg−1), probably due to low temperatures (8–23 °C) at Igeri. Fertilizers didn't cause significant differences in neither pathogen colonization nor AC at both sites. However, mean A. flavusaccumulation, as measured by pathogen host DNA ratio, was thrice (0.16) as high in sub-optimal fertilizer conditions compared to optimal fertilizer rate (0.05). All hybrids were susceptible to A. flavus and AC, though a difference in AC was noted among the hybrids at both sites. PAN 691 showed the highest AC (14.68 μg kg−1), whereas UHS 5210 had the lowest AC (1.87 μg kg−1). The susceptibility varied among the hybrids and was mostly associated with ear droopiness, husk tightness, days to 50% silking, 50% pollen shed, Anthesis to silking interval, diseased ears, insect damaged ears, kernel texture, dry matter, grain filling, ear height, kernel ash content and kernel moisture content. At Seatondale, A. flavus accumulation was positively correlated with aflatoxin (r = 0.606), and both A. flavus accumulation and AC were positively correlated with diseased ears. Selection and growing of less susceptible varieties under optimal fertilizer regime offer ideal strategy for sustainable reduction of A. flavus and aflatoxin contamination in maize at pre-harvest