Diversity and guaiacol production of Alicyclobacillus spp. from fruit juice and fruit-based beverages.

Alicyclobacillus acidoterrestris is an acido-thermophilic, spore-forming bacterial species that can spoil acidic fruit juice and fruit-based beverages. The metabolism of taint compounds by this bacterial species has led to its status as a targeted microorganism in the fruit juice industry. This study aims to assess the genetic diversity of Alicyclobacillus spp. including A. acidoterrestris and its correlation to spoilage taint metabolism. Alicyclobacillus cultures, which were previously isolated from a wide range of domestic and international products including fruit juice, fruit drinks and fruit juice concentrates, were subjected to DNA fingerprint analysis by using randomly amplified polymorphic DNA (RAPD) - polymerase chain reaction. Isolates were classified on the basis of their RAPD profile and the results were used to select representative strains to undergo taint production assessment. The taint guaiacol produced by Alicyclobacillus spp. was measured by headspace gas chromatography and mass spectrometry. From produced RAPD profiles, two genotypic groups and two sub-groups were identified. The groups were independent of product types and geographical origins. A significant number of isolates were clustered in genotypic group I, including A. acidoterrestris ATCC 49025. These isolates produced significant levels of guaiacol, 8.7 mg/L on average. A smaller number of isolates was found in genotypic group II including A. acidocaldarius and they produced no guaiacol. Primer F-64 was useful to identify Alicyclobacillus at the species level, and permitted rapid identification of strains producing fruit juice taint compounds such as guaiacol.

Inhibition, Injury, and Inactivation of Four Psychrotrophic Foodborne Bacteria by the Preservatives Methyl ρ-Hydroxybenzoate and Potassium Sorbate.

The minimum inhibitory concentrations (MICs) of methyl ρ-hydroxybenzoate (methyl paraben) and potassium sorbate for four psychrotrophic bacteria were compared at pH 5 and 6 and at 5 and 30°C. The bacteria tested were Listeria monocytogenes , Pseudomonas putida , Yersinia enterocolitica , and Aeromonas hydrophila . L. monocytogenes was generally the most resistant and A. hydrophila the least resistant to the preservatives. The differences between the bacteria were substantial. The MICs of the two preservatives were similar at pH 5, but at pH 6 the MICs of paraben were well below those of sorbate, except in the case of A. hydrophila . The MICs at 5°C were much lower than those observed at 30°C for all of the bacteria except P. putida . All four bacteria were inhibited by 1000 mg methyl paraben per L at 5°C. Exposure of the bacteria to concentrations of preservative that permitted growth at 30°C did not lead to adaptation to the preservative. The death rates of the bacteria in media containing 1000 mg methyl paraben per L varied over a wide range. At 5°C, a 3 log10 decrease in viable counts of L. monocytogenes and A. hydrophila took >4 months and a few days, respectively. Injury of L. monocytogenes , Y. enterocolitica , and A. hydrophila was detected under these conditions. Repair of the injury was demonstrated, with up to 24 h required for complete recovery. The type of buffer in which the test medium was prepared affected the preservative MICs and rate of injury of L. monocytogenes .