Growth behavior of off-flavor-forming microorganisms in apple juice.

Alicyclobacillus acidoterrestris and Streptomyces griseus griseus are two bacteria species that are frequently found in apple juice as spoilage bacteria. They both show thermoacidophilic behavior, adapting to the low pH of the juices and being able to survive high temperatures. They are able to regerminate in the shelf-stable product and spoil the juice by the formation of off-flavor compounds (i.e., guaiacol and 2,6-dibromophenol as metabolites of A. acidoterrestris and 2-isopropyl-3-methoxypyrazine, 2-methylisoborneol, 2-isobutyl-3-methoxypyrazine, and geosmin as important metabolites of S. griseus). In this study the growth behavior of the strains and the impact on apple juice were investigated under different conditions (i.e., temperature, oxygen supply, and mutual influence of the strains). The off-flavor formation was monitored by GC-MS after headspace SPME and subsequent calculation of the odor activity values. The results showed that S. griseus grows and consequently spoils the product even at 4 degrees C, whereas A. acidoterrestris needs at least room temperature to show significant growth. Limited oxygen supply did not significantly reduce off-flavor formation for any of the strains. The simultaneous presence of the strains in the juice reduced the growth of both species; nevertheless, off-flavor was detected.