Alternaria mycotoxins in soybean harvested in Argentina

OVIEDO M.S; RAMIREZ M.L.; BARROS G.G.; CHULZE S.N.

Tull, Austria

Conferencia; ISM Conference, Worldwide Mycotoxin Reduction in Food and Feed Chains; 2009

International Society for Mycotoxicology

Soybean (Glycine max L. Merr.) is an Asiatic leguminous plant cultivated in many parts of the world for its oil and proteins, which are extensively used in the manufacture of animal and human foodstuffs. Around 70% of the soybean harvested in Argentina is processed, providing 81% and 36% of the world´s exported soybean oil and meal, respectively. Both pre and post harvest soybean can suffer fungal contamination affecting the quality and safety of the raw material and by products. Alternaria and Fusarium species are the most commonly isolated fungi from soybean in Argentina and in other regions of the world. Alternaria toxins have recently received increasing attention, both in research programmers as well as in risk assessment studies. At present there are no statutory or guideline limits set for Alternaria mycotoxins by regulatory authorities. Considering the toxicity of these mycotoxins and their potencial co-occurrence with other mycotoxins, studies are necessary to develop strategies to reduce the entry of these toxins to the food and feed chains. The aims of this work were: i) to isolate and identify the Alternaria species from soybean and to determine their toxigenic profile, ii) to determine the impact of aW, temperature and incubation time on growth and alternariol (AOH), alternariol monomethyl ether (AME) and tenuazonic acid (TA) production by A. alternata on soybean-extract medium and iii) to evaluate a method for determine natural occurrence of Alternaria mycotoxins (AOH and AME) in soybean by HPLC coupled to SPE column clean up. From a two harvest season surveys only A. alternata was isolated during 2006/2007 harvest season, while A. alternata and A. infectoria were isolated during 2007/2008 harvest season.  A. alternata strains were able to grow at all temperatures tested in this study, ranging from 5 to 30 ºC, with an optimum between 25-30 ºC. The optimum aW to grow, seem to be at 0.995. Maximum amounts of AOH, AME and TA were obtained at 25 º and 30 ºC. The optimum aW for AOH and TA production was 0.98. However the aW for maximum AME production was 0.92 and 0.94 depending of the strain used. All the conditions of aW and temperature were maximum production of the three toxins are frequents during soybean development in the field. The methodology evaluated for study natural occurrence of AOH and AME in soybean, showed acceptable levels of recovery for both toxins, and good intralaboratory reproducibility. Mean recoveries of AOH and AME from soybean spiked at levels between 0.5 and 3 µg/g were 92.82% and 100,37%, respectively. Limits of detection was 8 and 16 ng/g for AOH and AME, respectively, based on the signal to noise ratio (3:1) and the limit of quantitation was established as 3 times the limit of detection (24 and 48 ng/g).