Evaluation of mycotoxin content in soybean (<i>Glycine max</i> l.) grown in Rwanda

Abstract

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, Rwanda