Impact of environment and interspecific interactions between spoilage fungi and Aspergillus ochraceus on growth and ochratoxin production in maize grain

Using layers of irradiated but still fertile maize grain, the effects of wa ter activity (0.995, 0.95 a(w)) and temperature (18, 30 degrees C) on inter specific interactions between Aspergillus ochraceus and five other spoilage fungi were examined. Asp. ochraceus was not competitive against Asp. flavu s, Asp. niger, or Alternaria alternate at 18 degrees C when water was freel y available (0.995 a(w)), while at 0.95 a(w) it was dominant against Asp. c andidus, Asp. flavus and Alt. alternata. At 30 degrees C and 0.995 a(w), As p. ochraceus was dominated by other fungi, except Alt. alternata, and was m utually antagonistic to Asp. candidus and Eurotium amstelodami. However, at 30 degrees C and 0.95 a(w) it was competitive against Asp. candidus and Al t. alternata, but not against the other species examined. The overall Index of Dominance showed that Asp. ochraceus was not competitive under the cond itions examined here. At 18 degrees C ochratoxin production by Asp. ochrace us was inhibited significantly by Asp. candidus (0.995 and 0.95 a(w)) and A sp. niger (0.995 a(w)). When grown on maize grain at 30 degrees C, ochratox in production by Asp. ochraceus was significantly inhibited by other spoila ge fungi when both were grown on maize grain, especially by Asp. niger and E. amstelodami (0.995 a(w)) and Asp. flavus at 0.95 a(w). These results sug gest that, to a large extent, A. ochraceus is not as competitive as some ot her spoilage fungi in primary resource capture on maize grain at a(w) of 0. 95 or above, although it may modify resource quality and influence secondar y colonisation by other species under the conditions tested. (C) 2000 Elsev ier Science B.V. All rights reserved.