Combined effects of low pH and cinnamaldehyde on the inhibition of Alicyclobacillus acidoterrestris spores in a laboratory medium

This study has focused on the inhibition of Alicyclobacillus acidoterrestris spores through the use of cinnamaldehyde at different pH values. The assays were performed in vitro in malt extract broth and two strains of A. acidoterrestris (c8 and c24) were used as target microorganisms. The amount of the active compound (0-200 ppm) and the pH (3.5-5.5) of the medium were modulated according to a two-variable five-level central composite design. Experimental data were modeled through the modified Gompertz equation; then the derived parameters were submitted to a stepwise regression. The results pointed out that a low pH enhanced the antimicrobial activity of cinnamaldehyde; moreover, its effectiveness was dose-dependent, as low doses caused a reversible inhibition of germination (i.e., the prolongation of the lag phase), whereas high amounts (150-200 ppm) determined a loss of the germinating ability. An intraspecies sensitivity of A. acidoterrestris to cinnamaldehyde was recorded and the strain c24 was more sensitive to the active compound.