Penicillium expansum was the most frequently isolated fungal species in
all tested samples of moulded apple fruits. The optimum temperature and
RH for the growth of this fungus and for patulin production were 25oC
and 90%, respectively, and the high amount of patulin was expressed by
isolate 3 at 18ºC (345.6 mg/ml-1). The production of patulin correlated
well with colony diameter and mycelium dry weight. Examined isolates
varied in their inhibitory activity against Escherichia coli and Bacillus
subtilis (isolate 3 had the best activity). The effect of propionic acid
(0.05-0.2%) and sodium benzoate concentrations (0.05-0.4%) on the
growth of P. expansum (isolate 3) and production of patulin from
moulded apple surface were investigated. Propionic acid (0.15%) and
sodium benzoate (0.3%) reduced the growth of the fungus and patulin
concentration by more than 70%. Propionic acid at a concentration of 0.2
% and sodium benzoate at more than 0.3% almost prevented the growth
of the fungus in the culture medium.