Effect of weak acids, combined with pH and temperature, on the growth or inactivation of Alicyclobacillus acidoterrestris

Alicyclobacillus acidoterrestris is a thermophilic, acidophilic, and spore-forming microorganism, able to spoil fruit juices. Few data are available on the effects of different acids of juices; thus, the goal of this research was to study the effect of 5 weak acids (malic, citric, ascorbic, tartaric, and lactic acids), compared to hydrochloric acid (strong acid, control) on two isolates of A. acidoterrestris from soil (C1 and C13). Acids were combined through a full randomized design with pH (2, 3, and 4), temperature (5 or 45 °C) and duration of storage (2, 7 and 14 days) as categorical predictors. Total population (spores + cells) and spores were assessed. The results of this paper suggest that acid-resistance of A. acidoterrestris could be strongly affected by the kind of acid; on total population, malic and ascorbic acids exerted the highest antimicrobial action, probably depending on pKa and acid concentration, but also on other factors (for example the size and the ability of acids to enter the cells). Results also confirm that weak acids could mainly act on activated spores/cells, rather than on spores. To some extent, acids could play an antimicrobial effect also on spores mainly at pH 2. In conclusion, this paper offers a first insight on potentialities and limits of weak acids on A. acidoterrestris and could contribute to understand the growth/inactivation of this spoiling microorganism, as a preliminary step to design and/or optimize new approaches for controlling it.