Growth and aflatoxin production of Aspergillus flavus in wheat and barley

Abstract

Growth rates and aflatoxin production of eight strains of Aspergillus flavus grown in wheat and barley were studied over temperature and water activity (aw) ranges of 10–42.5 °C and 0.80–0.975 respectively. Growth and aflatoxin production were restricted by low temperature, low (aw) and high temperature but not by high (aw). At 15° the lowest temperature at which growth occurred, an (aw) of 0.95 was needed for growth. At 42.5° growth was severely restricted and aflatoxin production altogether inhibited. The optimum temperature for growth was 35°; at lower temperatures (15°, 20°) the optimum (aw) was > 0.975, but at temperatures above these, it was 0.95. No single optimum temperature for aflatoxin production was determined but at (aw) s over 0.90 it lay between 25° and 35°. Strains showed marked differences in ability to produce aflatoxins but no equivalent differences in their growth rates. Only at the most favourable condition was a significant difference in growth demonstrated between two isolates at the extreme ends of the scale. There were not significant differences in growth or aflatoxin production between wheat and barley as substrates.