Utilization of potassium sorbate by tobacco spoilage fungi

Abstract

Aspergillus, Eurotium and Penicillium species (total of 11 isolates) were examined for their ability to utilize potassium sorbate as a sole carbon source in liquid culture, under different pH and temperature conditions. Of these, only A. flavus, A. versicolor and P. chrysogenum were able to grow in the presence of 0·1 to 0·4% (w/v) sorbate at pH 6·0 and 25 °C. Only A. Flavus was able to utilize up to 0·1% sorbate at pH 5·0 and 25° but not at 30°. Growth of these three species was stimulated by increased sorbate concentrations. In Burley and Virginia (low and high sugar substrates) extract broths, both A. flavus and P. chrysogenum were able to grow in the presence of up to 0·4 % sorbate. With the exception of P. chrysogenum in Burley extract, growth was significantly stimulated by increased sorbate concentration at both 25° and 30°, especially at pH 6·0. Further, in 0·4% sorbate and 25° growth of A. flavus was found to be directly proportional to sorbate depletion and was markedly higher in the low-sugar Burley extract than high-sugar Virginia extract. Optimum mycelial dry weights after eight days were associated with about 90% depletion of 0·4% sorbate in Burley and 70% in Virginia extract