This study aims to quantify and identify phenolic compounds in the hydroethanolic extract of Mentha piperita L. harvested in the Algerian Sahara by colorimetric and LC-MS/MS analysis, assess its antioxidant capacity by DPPH and ABTS assays and examine the impact of its inclusion at 2 to 6% rates on sensory and oxidative properties (DPPH, ABTS, TEBARS) and the lipid profile analyzed by GC-FID in steamed yoghurt. The extract contained 41.29 mg GAE/ml total phenolics, 22.45 mg QE/ml total flavonoids and only 0.59 mg CE/ml condensed tannins. LCMS/MS analysis detected 26 phenolic compounds, among which rosmarinic acid was the most abundant. DPPH and ABTS assays showed IC50 values of 3.18 and 2.49 mg freeze-dried extract/ml, indicating the high antioxidant potential of the examined extract. Yogurts containing 2% and 4% of this extract were well accepted by the sensory evaluation panel. The studied extract also significantly increased the antioxidant capacity of yogurt up to 39.51% compared to natural yogurt after 20 days of refrigeration, significantly reduced lipid peroxidation and at a dose of 4%, caused a significant improvement (p<0, 01) in the omega content of yogurt, especially alpha-linolenic acid, compared to the control and caused a marked decrease (p<0. 01) in the ω-6/ω-3 ratio in yogurt from 5.21 to 4.11 on day 20 of refrigeration compared with the control. The production of a sensorially acceptable pasteurized yogurt enriched with up to 4% hydroethanol extract of Mentha piperita L. as an alternative to synthetic antioxidant additives with health-promoting properties appears feasible.

This study contributes to the evaluation of the antibacterial effect of hy-droethanolic extract of peppermint (Mentha piperita L.) rich in phenolic compounds on the growth of reference bacterial strains Streptococcus ther-mophilus (ATCC19258) and Lactobacillus bulgaricus (ATCC11842) as well as the consequences of its addition at a dose of 6% on the quality of a steamed yoghurt. The phenolic compounds of peppermint collected in Algeria were extracted from the ground leaves of the plant in a hydroethanolic solution. The antimicrobial activity of peppermint extract and the quality of yoghurt were assessed by the following measures: bacterial growth test, disc diffu-sion test, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), pH, acidity, viscosity and the organoleptic tests (taste, odor, color and freshness). The results revealed that hydroethanolic extract of M. piperita L. had 25 mg GAE/ml of extract of total phenolic compound and a content of 8.28 mg QE/ml of extract of flavonoids. This extract had a bactericidal against S. thermophilus and a bacteriostatic inhibitory effect against L. bulgaricus. The addition of phenolic compounds of M. piperita L. at 154.02 mg GAE/100ml significantly reduced (p<0.05) acidity, viscosity, and the germ increase of S. thermophilus and L. bulgaricus in steamed yogurt prepared with 6% of hydroethanolic extract of the studied plant compared to the control. However, the fermented milk treated with the 6% of pepper-mint extract was very well appreciated by the tasting jury, just like the yo-ghurt control.