The heat stability of ochratoxin A in green coffee beans inoculated with Aspergillus ochraceus was studied. Heat treatment (roasting) at 200 degrees C for 10 or 20 min reduced the levels of ochratoxin A by only 0-12% in the dried whole beans. Almost all of the ochratoxin A was infused into the coffee decoction when the roasted samples were ground and extracted with boiling water. Therefore, the reduction of ochratoxin A concentration of contaminated coffee beans by roasting under these conditions is ineffective.

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The growth and ochratoxin A production of Aspergillus ochraceus strains S-235-100 and IFM 0458, which were isolated from green coffee beans and glutinous rice, respectively, were examined in yeast extract-sucrose (YES) medium containing 0.1 to 1.0% caffeine. The mycelial growth and ochratoxin A formation of strain IFM 0458 was inhibited by caffeine at concentrations over 0.1%, and ochratoxin A was not produced at caffeine levels of 0.5% and 1.0%. Contrary to this, A. ochraceus strain S-235-100 produced a larger amount of ochratoxin A in the presence of 0.5% and 1.0% caffeine when grown on YES medium, reaching a maximum after 15 to 20 days of incubation. The formation of ochratoxin A by nine additional strains of A. ochraceus, three strains of A. elegans and one strain of A. sclerotiorum isolated from green coffee beans was determined on rice and ground green coffee media. A significant degree of degradation of caffeine in the green coffee medium was demonstrated with cultures of nine A. ochraceus isolates from green coffee beans. Most of these isolates showed the potential to grow on moist green coffee beans and to produce a significant amount of ochratoxins.

Analyses of ochratoxin A (OTA) and aflatoxins (AFs) in 94 imported beer samples from 31 producing countries and in 22 Japanese beer samples were performed by immunoaffinity column and reversed-phase liquid chromatography (LC) with fluorescence detection. Recoveries of OTA from beer samples spiked at 25 and 250 pg/mL were 86.1 and 88.2%, respectively. Recoveries of AFs were 98.4 and 98.9%, 95.4 and 95.5%, 101.2 and 97.8%, and 98.9 and 96.0%, respectively, from beer samples spiked at 4.1 and 41 pg AF B1, 4.45 and 44.5 pg AF B2,4.7 and 47 pg AF G1, and 4.65 and 46.5 pg AF G2/mL. Detection limits were 1.0 pg/mL for OTA, 0.5 pg/mL for AFs B1 and B2, and 1.0 pg/mL for AFs G1 and G2. OTA was detected in 86 (91.5%) of 94 imported beer samples at a mean level of 10.1 pg/mL and in 21 (95.5%) of 22 Japanese beer samples at a mean level of 12.5 pg/mL. AF B1 was detected in 11 of 94 imported beer samples at a level of 0.5–83.1 pg/mL and in 2 of 22 Japanese beer samples at 0.5 and 0.8 pg/mL. Except for one beer sample from Peru, the samples contaminated with AFs were also contaminated with OTA. Although OTA was detected in most samples from various countries, AFs were detected in the beer samples from only a limited number of countries where AF contamination might be expected to occur because of their warm climate.

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