Effets d’extrait à l’hexane aqueux de Mentha pipérita L (Menthe poivrée) sur la qualité d’un lait fermenté (type yaourt étuvée.

Abstract

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.