The use of
essential oils in
foods has attracted great interest, due to their antagonistic action against pathogenic microorganisms. However, this action is undesirable for
probiotic foods, as products containing
Lactobacillus rhamnosus. The aim of the present study was to
measure the
sensitivity profile of L. rhamnosus and a
yogurt starter
culture in fermented
milk, upon addition of increasing concentrations of
cinnamon,
clove and
mint essential oils.
Essential oils were prepared by
steam distillation, and chemically characterised by
gas chromatography-mass spectrometry (GC-MS) and
determination of density.
Survival curves were obtained from counts of L. rhamnosus and the starter
culture (alone and in combination), upon addition of 0.04%
essential oils. In parallel, titratable
acidity was monitored over 28 experimental days.
Minimum inhibitory concentration values, obtained using the microdilution
method in
Brain Heart Infusion medium, were 0.025, 0.2 and 0.4% for
cinnamon,
clove and
mint essential oils, respectively.
Cinnamon essential oil had the highest antimicrobial activity, especially against the starter
culture, interfering with
lactic acid production. Although viable
cell counts of L. rhamnosus were lower following
treatment with all 3
essential oils, relative to controls, these results were not statistically significant; in addition,
cell counts remained greater than the minimum count of 10(8)CFU/mL required for a product to be considered a
probiotic. Thus, although use of
cinnamon essential oil in
yogurt makes starter
culture fermentation unfeasible, it does not prevent the application of L. rhamnosus to
probiotic fermented
milk. Furthermore,
clove and
mint essential oil caused sublethal stress to L. rhamnosus.