Safety Aspect in Soybean Food and Feed Chains: Fungal and Mycotoxins contamination

BARROS, G.; RAMIREZ, M.L.; CHULZE, S.

Soybean- Biochemestry, Chemistry and Physiology

Intech

Año: 2011; p. 7 - 20

In Argentina, in the last quarter century, soybean production increased at an unprecedented rate increasing the planted area from 38,000 hectares in 1970 to 16 million hectares today, with an average production around 40.5 million tons per year. Around 70% of the soybean harvested is processed, providing 81% of the world´s exported soybean oil and 36% of soybean meal. Hygienic safety of soybean and by-products depends on fungal contamination among other microorganisms. However, with European Union legislation imminent, the consideration of mycotoxins is becoming increasingly important. In a first approach, we stared to examine the fungal and mycotoxin contamination on soybean used in the soy meal production to identified critical control points (CCPs) in the process. Among the trichothecenes, deoxynivalenol (DON) was detected in different points of the process at ppm levels. However, F. graminearum, the main responsible for cereal contamination with DON in Argentina, was not recovered. Based on these results, the dynamic of Fusarium species potentially toxigenic at different soybean growth stages and natural occurrence of several trichothecenes (DON, Nivalenol, T-2 and HT-2 toxins) was analysed. Respect to Fusarium contamination across different stages, the high isolation frequency were detected in pods and seeds at stage R6 (full seed), being the aw of immature seeds 0.992.  At stage R8 (full maturity), the water content of the seeds dropped dramatically to 0.700 and the percentage of Fusarium spp. also diminished compared to stage R6. Among the Fusarium species identified, F. equiseti the most frequently recovered from flowers, pods and seeds followed by F. semitectum and F. graminearum. Similar to Fusarium species, Alternaria spp. showed high mean isolation frequency on flowers, pods and seeds, at similar levels across all stages. Although this organism is considered to be nonpathogenic on soybean plant (Roy et al., 2000), it is relevant to considered that previous studies have demonstrated tenuazonic acid production by A. alternata on soybean-based agar (Oviedo et al., 2009a) and natural occurrence of alternariol and alternariol monomethyl ether on soybean seed (data unpublished). Respect to trichothecenes contamination, DON was detected at ppm levels in a few samples obtained from R6 and R8 stages. This is the first report that demonstrates DON contamination on soybean during grain ripening. Based on the DON contamination on soybean seeds at stages R6 and R8, we considered interesting to investigate the toxigenic ability of isolates belonging to F. graminearum species complex. Strains of F. graminearum usually express one of three sets of trichothecene metabolites either: nivalenol and acetylated derivatives (NIV chemotype), (ii) deoxynivalenol and 3-acetyldeoxynivalenol (3-ADON chemotype), or deoxynivalenol and 15- acetyldeoxynivalenol (15-ADON chemotype) (Ward et al. 2002). Surprisingly, Fusarium isolates that produce both DON and NIV (NIV/DON chemotype) have been reported and described as “unknown” chemotypes (Ward et al. 2002; Quarta et al. 2006). Due to the toxicological differences between NIV and DON, it is important to survey the presence of different chemotypes in a given region and different crops.