Effet des extraits phénoliques d'ail (Allium sativum. L) sur la croissance des bactéries lactiques (Streptococcus thermophilus et Lactobacillus bulgaricus)

Abstract

The purpose of this study, focuses on the achievement of a comparison between the different inhibitor of phenolic extracts (extract obtained by maceration method and the method of MACHEÏX), from two varieties of garlic (red Var, white Var) on growth of lactic bacteria (Lactobacillus bulgaricus and Streptococcus thermophilus).

Two evaluation methods were adopted, the method of agar diffusion and the method of direct contact. The results have been subjected to a statistical study to compare the effects of different extracts at different concentration (0%, 1%, 2%, 5%) and to define the most discriminating.

The experimental work was supplemented by a study in-situ, which is summarized in the preparation of fresh cheese with the addition of both lactic and garlic extract, in order to study the effect of the latter on the coagulant activity of the strains, and also their influence on the microbiological quality of finished product. Tasting tests were conducted to evaluate the organoleptic and sensory qualities.

The experimental results show that:

1. Polyphenolic extracts obtained by maceration are more concentrated than those obtained by method of MACHEÏX; 2. The results of the tow phenolic varieties of garlic have no significant effect on the growth of ferments tested by the method of agar because the zones of inhibition were less than 15mm and the strains tested are insensitive to variation doses of extracts (%, 2%, 5%). 3. The method of direct contact has found that extracts of garlic white and red has no bactericidal effects against S. thermophilus and L. bulgaricus because the rats of inhibition doses not exceed 5,56% for the first and 5.80% for the second strains. The two methods of assessment for the case of bacterial strains used gave the same results ; 4. regarding the study in-situ, it was found that adding extracts of garlic and milk enzymes have an effect on the microbiological quality and sensory where the Freidman test showed that there are any significant differences between samples of cheese in a few parameters (odor, taste, acidity, texture), in addition to the coagulant activity of lactic bacteria is not delayed by the addition of garlic extract.