Effects of potassium sorbate and environmental factors on growth of tobacco spoilage fungi

Abstract

Potassium sorbate was found to inhibit germination and growth of a range of spoilage fungi isolated from tobacco below pH 5. However, at and above pH 5 the efficacy of potassium sorbate was influenced by substrate composition and water activity (aw). Eurotium spp., Aspergillus flavus, A. fumigatus, A. niger, and Penicillium species all grew with 0·1–0·3% sorbate at 0·95 aw on ma Virginia and Burley extract agars. However, at 0·85 aw, only Eurotium spp., A. flavus, P. chrysogenum and P. viridicatum were able to grow in the presence of sorbate. At both high and low aw the tolerance of sorbate was influenced by substrate composition. The lag time for growth initiation in different concentrations of sorbate was significantly influenced by substrate composition for E. amstelodami and P. chrysogenum but not for A. niger. Growth of E. amstelodami, A. flavus and P. chrysogenum was significantly less on Burley extract agar than Virginia extract or malt agar over the range 0·75–0·90 aw at pH 5 and 6·5 and with 0·1–0·4% sorbate. Under some environmental conditions, growth of E. amstelodami on tobacco extract agars was stimulated by sorbate