A Brazilian study 1 into essential oils and probiotic bacteria has found that essential oils inhibit Lactobacillus rhamnosus and other starter cultures in fermented milk across its shelf life.

L. rhamnosus is known to inhabit the vagina in many populations of healthy women with normal vaginal flora, however the purpose of this study was in food science – the need to eradicate pathogenic bacteria from cultured milk products means finding novel ways of selectively killing certain bacteria. There is some possibility that essential oils could provide this selective role in yoghurt products.

The study

The researchers set out to see what impact various concentrations of cinnamon, clove and mint essential oils had on L. rhamnosus and a yoghurt starter culture in fermented milk.

Findings

  • Cinnamon essential oil had the highest antimicrobial activity, particularly in the starter culture, as it interfered with lactic acid production.
  • Viable cell counts of L. rhamnosus were found in all three essential oils, although these were not statistically significant.
  • Cell counts remained greater than the minimum count required for a product to be deemed a probiotic product.
  • Cinnamon essential oil in yoghurt makes starter culture unfeasible.
  • Cinnamon essential oil does not prevent the application of  L. rhamnosus to probiotic fermented milk.
  • Clove and mint cause sublethal stress to L. rhamnosus.
  • The use of these essential oils does not impair the fermentation process during fermented milk product preparation, suggesting the bacteria are resistant to mit and clove essential oils.
  • Cinnamon essential oil had a significant impact on the starter culture count and lead to lower lactic acid production, similar to clove and mint essential oils.
  • L. rhamnosus was not significantly affected by cinnamon essential oil.

Specific essential oils used:

  • Cinnamon (Cinnamomum zeylanicum)
  • Clove (Syzygium aromaticum L.)
  • Mint (Mentha piperita L.)

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  1. Brazilian Journal of Microbiology, Braz. J. Microbiol. vol.43 no.3 São Paulo July/Sept. 2012, Inhibitory effect of essential oils against Lactobacillus rhamnosus and starter culture in fermented milk during its shelf-life period, Cristiane Mengue, Feniman Moritz, Vera Lúcia, Mores Rall, Margarida Júri Saeki; and Ary Fernandes Júnior

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