The impact of water and temperature interactions on lag phase, growth and potential ochratoxin A production by two new species, Aspergillus aculeatinus and A. sclerotiicarbonarius, on a green coffee-based medium

Abstract

Two new species of Aspergillus (A. aculeatinus, A. sclerotiicarbonarius) were previously isolated from coffee in Thailand. The objective of this study was to examine the effect of interacting environmental factors of water availability (water activity, aw) and temperature on lag phases prior to growth, growth and potential for ochratoxin A (OTA) production by three strains of each species on a green coffee-based medium for the first time. This showed that overall the growth of the three strains of each species was similar over the 20-37°C and 0.85-0.99 aw ranges. The lag phase prior to growth was <1day at 0.95-0.98 aw and 25-37°C and increased to 2-3 days at marginal temperatures and aw levels. The growth of strains of the uniseriate species A. aculeatinus was optimum at 0.98 aw and 30-35°C. For the biseriate A. sclerotiicarbonarius strains this was 0.99 aw and 30°C. This species was not able to grow at 37°C. None of the strains of the two species grew at 0.85 aw, regardless of temperature. Integrated profiles based on the data from three strains of each species have been developed to show the optimum, maximum and marginal conditions of interacting aw and temperature conditions for growth. None of the strains produced OTA on a green coffee-based medium. This information is important as these species are part of the mycobiota of coffee and may influence OTA contamination by other ochratoxigenic species during coffee processing.

Keywords: Aspergillus; Coffee; Ecology; Growth; Temperature; Water activity.