Inhibitory activity of lactic and acetic acid on Aspergillus flavus growth for food preservation

In this study acetic and lactic acid Minimal Inhibitory Concentration (MIC) were determined for different Aspergillus flavus strains in solid medium: toxigenic strains A. flavus AFUNL1, AFUNL2 and AFUNL3; and a non-toxigenic strain A. flavus AFUNQ6. A. flavus AFUNQ6 was the most resistant strain to acetic acid, with a MIC value of 41.6 mM (pH 4,62) while acetic acid MIC was the same for the three toxigenic strains (38.1 mM, pH 4.69), the lactic acid MIC was different for all the strains: 357.7 mM (pH 2.74), 405.4 mM (pH 2.69), 274.2 mM (pH 2.95) and 393.4 mM (pH 2.59) for A. flavus AFUNQ6, AFUNL1, AFUNL2 and AFUNL3 respectively. MIC values for non dissociated lactic acid were almost tenfold higher than MIC vales for non dissociated acetic acid for the A. flavus strains. Growth kinetic parameters: growth rate (KD) and lag phase were determined to evaluate fungal inhibition. An increase of undissociated acid concentration produced a decrease in KD values and an increase in lag phase duration. Lactic and acetic acid mixtures showed a synergistic effect, reducing the concentration necessary of every acid in the mixture for fungal inhibition compared with the individual MIC values. The minimal acids mixture that obtained the fungal inhibition for all the strains was lactic acid 78 mM acetic Acid 31.2 mM at a pH 3.4.