Modelling of aflatoxin production by Aspergillus parasiticus in a solid medium at different temperatures, pH and propionic acid concentrations

The effect of pH (5.5 and 5.9), propionic acid concentration (129, 258 and 516 ppm) and temperature (25, 30 and 36 C) on aflatoxin production by Aspergillus parasiticus in solid media at controlled water activity 0.95 was studied. Modelling of aflatoxin production was carried out using adequate equations to obtain the maximum aflatoxin concentration (C values) and the corresponding time to reach the maximum (a values). For control samples, the highest C values were observed for aflatoxin B1 and G1. The effect of temperature on aflatoxin production at different pH was analysed using a function derived from the Arrhenius equation. Optimum temperatures for aflatoxin production were 27.84 and 27.32 degreesC at pH 5.9 and 5.5. respectively. Two indices were defined in order to analyse the effect of undissociated propionic acid concentration (uac) on C and a values. Propionic acid showed the highest inhibition on C values for aflatoxin G1 and on a values for aflatoxin B1. Concentrations over 60 ppm uac did not show an increase in both indices indicating that there is no need to increase the concentration of propionic acid over this value. These plots may be useful for technological purposes and to identify conditions (pH, propionic acid and storage temperature) to inhibit aflatoxin production in foodstuffs. (C) 2002 Elsevier Science Ltd. All rights reserved.