Research – How do Time, Tannin and Moisture Content Influence on Toxicogenic Fungal Populations during the Storage of Sorghum Grains?

Journal of Food Protection

Cereal grains are usually ensiled to improve their nutritional value and are one of the main sources of feed for dairy cattle. However, during storage, grains can be contaminated with toxicogenic fungi. Sorghum is one of the most economically important cereals in the world. Therefore, the aim of this work was to evaluate the influence of storage duration and tannin and moisture contents on toxicogenic fungal populations in sorghum grain storage. Samples were prepared with variety high in tannins (genotypes Morgan 108 and ACA 558, >5g/kg DM) and with variety low tannin content (genotypes Flash 10 and ACA 546, <1g/kg DM) were collected and manually compacted in experimental laboratory silos where they received different moisture content treatments, namely low (15-25%), medium (26-32%) and high (33-42%). Freshly harvest grains were analyzed at time 0 and storage grains were analyzed at different times (30, 90 and 180 days). Fungal isolation and identification were performed following conventional mycological methods. Penicillium citrinum (34%), Aspergillus flavus (60%) and Fusarium nygamai (68%) were the most abundant species. Rapid detection of aflatoxins and fumonisins in each sample was performed by ELISA according to the AOAC method, and the quantification of aflatoxin B 1 was performed by HPLC. Aflatoxins were detected in four samples with levels of 6.7-28.8 µg/kg and aflatoxin B 1 with a level of 2-14 µg/kg in pre- and post-storage grains . Fumonisins were only detected in two freshly harvested samples with levels of 500-900 µg/kg . In general, the storage time favored the increase of Penicillium population, instead the Aspergillus and Fusarium are reduced. Conversely the abundance of the three population was not affected by the moisture content. The results of this study show that fungal population must be analyzed at different times.

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