Study of the interspecific inhibitioncompetition phenomena in between ochratoxinogenic strains present on coffee beans : J-67

The use of bio-competition between little or non-toxigenic strains against toxigenic strains is a strategy to prevent the presence of OTA in coffee. The examples reported in the literature focus on competition between yeasts and bacteria and ochratoxinogenic fungi. Usually, examples of studies on fungi included strains of Aspergillus niger aggregate or nonproducing Penicillium whose presence inhibited the accumulation of OTA during grape drying (Valero et al., 2007). Biological control by Trichoderma spp proved to be an effective method to prevent bunch rot which promotes contamination by other fungi that can be toxigenic (Elad, 1994; Harman et al., 1996; Harman et al., 2004). Reducing OTA production can be obtained by inhibiting the growth and/or production of the toxin or by decontamination due to toxin consumption after its production by another strain. Some examples indeed stated of this phenomenon using Aspergillus section Nigri (Varga et al., 2000; Abrunhosa et al., 2002). It is within this framework that was undertaken trials with co-cultures of strains extracted from coffee to find and explore potential inhibitions and/or competitions against ochratoxinogenic strains. The main objective of this study was to identify possible inhibition and/or competition between Aspergillus strains with very different levels of OTA production: Aspergillus niger, A. ochraceus, A. westerdijkiae and A. carbonarius. A. westerdijkiae and A.ochraceus were confused during a long time due to their similar characteristics. A. westerdijkiae produced in artificial medium up to 30,000 ?g/Kg of OTA. In contact with A. ochraceus which is a weak OTA producer, its OTA production reduced to non detectable. We have shown that there was a real competition between strains of the section Circumdati and the section Nigri. The most interesting couples targets/competitors in terms of reducing the production were A. westerdijkiae/ A. niger and A. westerdijkiae/ A. ochraceus. We could conclude that in a natural environment, competition in between strains exits and helps to reduce OTA content. (Résumé d'auteur)