Behavior of Listeria monocytogenes in the presence of methylxanthines-caffeine and theobromine
Two components of cocoa powder, caffeine (1, 3, 7-trimethylxanthine) and theobromine (3,7-dimethylxanthine), were evaluated for their effect on growth of L. monocytogenes strain V7. Caffeine (0.5 percent) and theobromine (2.5 percent) were added singly or in combination to skim milk or a modified tryptose phosphate broth (MTPB), which were sterilized, inoculated to contain ca. 1 x 10 exponent 3 CFU L. monocytogenes/ml, and incubated at 30 grade centigrade. Both compounds allowed some growth of the pathogen; however, longer lag phases occurred in samples with (6 to 9 h) rather than without (minor 3 h) caffeine. Generation times at 30 grade centigrade ranged from 1.10 h (2.5 percent theobromine in broth) to 2.28 h (2.5 percent theobromine plus 0.5 percent caffeine in milk). Generation times were significantly (p minor 0.05) lengthened in the presence (2.17 h) rather than in the absence (1.2 h) of caffeine. Populations in samples without caffeine were more than ten times greater (8.57 log 10 CFU/ml) than in samples with caffeine (7.21 log 10 CFU/ml). Theobromine concentration (0 or 2.5 percent) and substrate (MTPB or skim milk) had only limited effects on growth of the pathogen. The change in pH of the medium was a function of the extent of growth of L. monocytogenes and the buffering capacity of the substrate. A smaller pH change (0.09 unit) occurred in the milk medium than in broth (0.48 unit) because of the minimal buffering capacity of the 0.2 percent tryptose solution. Samples with caffeine had a small decrease in pH (0.07 unit) because growth of L. monocytogenes was inhibited and thus acid production was minimal.
| Main Authors: | , |
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| Format: | biblioteca |
| Published: |
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| Subjects: | CACAO EN POLVO, LISTERIA MONOCYTOGENES, CAFEINA, TEOBROMINA, XANTINAS, POLUCION, |
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