In 0.5% caffeine-containing yeast extract-sucrose (YES) broth, the growth of 49 strains of aflatoxigenic and non-aflatoxigenic Aspergillus flavus and A, toxicarius which were isolated from peanuts, spices and green coffee beans was compared at 25°C after 7 days incubation. Although all strains from the peanuts and spices could not grow well on the caffeine-containing YES broth, the growth of three aflatoxigenic strains and one non-aflatoxigenic A, flavus from the green coffee beans was little affected (growth rate: 36.5-54.8%). These strains were confirmed as a caffeine-resistant, by further detailed experiments. Namely, the effects of caffeine on growth and aflatoxin production by the strains and residual caffeine in their culture filtrates were observed on the 0.5% caffeine-containing YES broth at intervals of 5 days in the period of 20 days. For the first 5 days, the growth of these strains was delayed by the addition of caffeine, but the growth was completely recovered after the 10 days. Aflatoxin production of one strain of A, flavus was inhibited by caffeine, but the two other strains produced a high level of aflatoxin B1 in the 0.5% caffeine-containing YES broth, reaching about the same or more amounts as the control after the 15 days of incubation. The added caffeine in the culture of these caffeine-resistant strains was degraded in the range of 10-91%.
