Investigating the effect alcoholic extract of Nepeta crispa on the antioxidant activity and microbial and sensory properties of doogh

Due to the richness of nutrients, especially at ambient temperature, doogh is prone to contamination with some microorganisms, which causes changes in the product flavor and its bloating during storage. Therefore, the use of natural antimicrobials such as Nepeta crispa exract to increase doogh shelf life while increasing its marketability can be important. The aim of this research was to investigate the effect of Nepeta crispa alcoholic extract on the qualitative properties of doogh. The compounds of Nepeta crispa extract were identified using GC-MS. Antioxidant activity, physicochemical (pH, acidity and viscosity), microbial (Escherichia coli and Staphylococcus aureus count) and sensory (taste, odour, texture and overall acceptance) characteristics of doogh containing different concentrations of Nepeta crispa extract (1.25, 2.5 and 5 mg/ml) were investigated during storage. ANOVA and Duncan test were used for statistical analysis. Thymol (53%) was the most identified compound in the extract of Nepeta crispa. The MIC of Nepeta crispa extract against E.coli and S.aureus was 2.5 and 1.5 mg/ml, respectively. The MBC of the extract against E.coli and S.aureus was 5 and 3 mg/ml, respectively. During storage, by adding plant extract, the acidity and viscosity of the samples increased and the pH decreased. Increasing the concentration of the extract increased the antioxidant and antimicrobial activity of doogh. The sample containing 2.5 mg/ml extract had the highest overall acceptance score, therefore, this sample was selected as the best treatment. Nepeta crispa extract has antimicrobial and antioxidant activities and might be used as a natural preservative in doogh.