Using regression and Multifactorial Analysis of Variance to assess the effect of ascorbic, citric, and malic acids on spores and activated spores of Alicyclobacillusacidoterrestris

Abstract

The type strain of the species Alicyclobacillus acidoterrestris (DSM 3922) and the strain CB1 (accession number: KP144333) were studied in this research to assess the effects of three weak acids (malic, citric, and ascorbic acids), pH (3 or 4), and spore status (spores, and activated spores). Acids were used to prepare 7 different blends, and the blends used to reduce the pH of Malt Extract broth to 3 and 4; then, media were inoculated with spores or activated spores, stored at 45 °C (optimal temperature for A. acidoterrestris growth), and analyzed immediately and after 2 and 7 days. Data were preliminary standardized as increase/reduction of microbial population, compared to the initial concentration, and modelled through two different statistical approaches (multifactorial ANOVA, and multiple regression). Finally, a binary code (0-no growth or reduction of viable count; 1-growth) was used to perform a multiple regression analysis on the growth probability of A. acidoterrestris. Generally, ascorbic acid was the most effective compound, but other acids (e.g., malic acid) could contribute to increase the inactivation ratio; concerning spore status, the highest sensitivity of activated spores suggests that acids probably act during the outgrowing phase. Finally, the two strains showed different trends at pH 3.0, being the type strain the most resistant one.

Keywords: Activated spores; Alicyclobacillus; DoE; MANOVA; Regression; Spores.