Effect of Propolis Extract as a Natural Preservative on the Microbial Content of Kareish Cheese

Abstract

The present study aimed to utilize propolis extract as natural preservative and attractive healthy ingredients on the microbial content of kareish cheese during storage. Effect of two extracts of proplis (ethanolic and water extract) were used at different concentrations on the growth of three bacterial strains, Streptococcus thermophilus, Lactobacillus bulgaricus and Bifdobacterium bifidium being used as starter. The affect of these extracts on some spoilage contaminants of dairy microorganisms in milk medium were also studied. The resultant kareish cheeses from different treatments (with ethanol and water propolis extracts) were analyzed for phenolic compounds, antioxidant activity, microbiological and sensory properties when fresh and during storage (28 day) at 5±1°C. The counts of Str. thermophilus and Lb. bulgaricus in milk with different concentrations of propolis extracts were significantly higher than those in control. Ethanol extraction of propolis (EEP) and water extraction of propolis (WEP) at 600 and 1000 mg /100ml displayed a bactericidal effect with all of the tested spoilage microorganisms.The addition of propolis extract had a negligible effect on the content of cheese moisture, and slight decrease in total protein of cheese was observed along the storage period. High acidity of kareish cheese observed with increasing the concentration of added propolis extracts. Addition of different concentrations (6 and 10%) of propolis extracts (ethanolic and water) increased of the phenolic compounds, flavonids and antioxidant activity with the increase of propolis extracts. The counts of Lb. bulgaricus and Str. thermophilus in kareish cheese treatments were significantly (p ≤ 0.05) higher than these in the control. However, counts of mesophilic (MBC) and psychrophilic (PBC), coliform bacteria and moulds & yeasts in kariesh cheese treatments were not detected until 21 days. Kareish cheeses made with water propolis extract (T3 andT4) were of higher sensory evaluation and with the best acceptablility during storage period, compared with cheese made by ethanolic propolis extract (T1 and T2).