Résumé:
This study aims at determining the effect of extracts with hexane of Menthapiperita harvested
in the wilaya of Ouaregla on the two specific yogurt germs namely Streptococcus
thermophilus and Lactobacillus bulgaricus and on the quality and the stability
(physicochemical, microbiological and organoleptic ) a fermented milk type yoghurt
parboiled during its storage at 4oC for 21 days.
Regarding the physicochemical results, the measured pH values are proportional, with the
concentration of Menthapiperita extract added to the experimental products. This trend is
reversed for the acidity of which net decreases in values are recorded with increasing doses of
Mennthapiperita extract added during the preparation of fermented milks.
Then, for the microbiological results, the number of specific yogurt germs namely
Streptococcus thermophilus and Lactobacillus bulgaricus appears to meet the standards
required for parboiled yoghurt; of 107 live germs / ml.
For organoleptic results, the use of Menthapiperita extract at low doses of 2% and 4% as an
adjunct to experimental yoghurt did not alter the main organoleptic criteria of the products.
However, fermented milks prepared at high doses of peppermint extract of 6% showed poor
organoleptic results.
The extraction of the bioactive compounds was carried out from the aerial part of the plant.
The extracts obtained were diluted to 20%, 40%, 60%, 80% and 100%. The measurements
and controls were carried out in triplicate tests. and concerned the direct contact method, the
disk diffusion method, the IJC and the CMB.
With a declining growth rate and inhibition diameters that are becoming increasingly
important by increasing the concentration of Menthapiperita extract, it has been possible to
demonstrate the inhibitory effect of the latter on the germs studied, which is in certain
relationship with the concentration of bioactive compounds in the plant of the study.
Moreover, the MIC and CMB of the two strains is obtained with the extract prepared
at MIC= 20% for Streptococcus thermophilus; MIC = 80% for Lactobacillus bulgaricus and
CMB = 100% for both strains.
The hexane extract of Peppermint from Ouaregla appears to exert a bactericidal effect on
Streptococcus thermophilus and bacteriostatic on Lactobacillus bulgaricus.
