الفهرس 
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Abstract
The present study was conducted at Dairy Department- Faculty of Agriculture- Mansoura University. The present study was designed to isolate and characterize potential adjunct cultures of lactic acid bacteria (LAB) from pickled Domiatti cheese and Ras cheese. Fifty-four cheese samples including 33 and 21 samples of pickled Domiatti cheese and Ras cheese, respectively were randomly collected from Mansoura city and villages in its vicinity and assessed for their flavor by panelists. Given the association of the adjunct cultures with typical flavor in cheese, cheese samples with ”good” or ”acceptable” flavor were further analyzed as a potential source of adjunct LAB cultures. A total of 162 suspected LAB isolates could be recovered from theses samples, of which 37 and 4 isolates were confirmed to belong to the Enterococcus and Lactobacillus genera, respectively. Enterococcus and Lactobacillus isolates were examined for technological properties including acidity development, proteolytic activity, and lipolytic activity. Isolates were also assessed for safety-associated traits including antibiotic resistance, biogenic amine production, and hemolytic activity. Three LAB cultures were selected to be used as adjunct cultures. This selection based on the technological and safety-related traits of those cultures. The effect of using selected adjunct cultures on the sensory properties and chemical composition of Domiatti cheese was also assessed. The results of the present study could be summarized as followsSensory evaluation of cheese samples: Cheese samples were divided into four groups. First group included 15 cheese samples with good flavor, second group included 15 cheese samples with acceptable flavor, third group included 17 cheese samples with poor flavor, and the fourth group included 7 cheese samples with unacceptable flavor. Isolation of potential LAB adjuncts: A total of 162 suspected LAB isolates could be recovered from cheese samples with ”good” or ”acceptable” flavor.Identification of potential LAB adjuncts: Thirty seven and four isolates were confirmed to belong to the Enterococcus and Lactobacillus genera. Acidity development by LAB cultures: Enterococcus isolates were more acidifiers than Lactobacillus isolates. There was variation between isolates in their ability to produce acid in milk. Proteolytic activity by LAB cultures: Eight Enterococcus isolates showed positive results for proteolytic activity by using the platting method. However, Enterococcus isolates could be divided into three groups by using the colorimetric method. Lactobacillus isolates showed positive results by using the platting method and gave results ranged from 32.1-45.7 µg tyrosine/ml by using the colorimetric method. Lipolytic activity by LAB cultures: Sixteen Enterococcus isolates showed positive results for lipolytic activity by using the platting method. Those isolates showed total volatile free fatty acids determination of 3.8-5.2. However, all Lactobacillus isolates showed positive results by using the platting method and gave results ranged from 3.7-3.9 for TVFFA.Antibiotic resistance: Enterococcus and Lactobacillus isolates showed variations in their ability to resist different antibiotics.Biogenic amine production and hemolytic activity: Six Enterococcus isolates were able to produce histamine, while 13 isolates were able to produce tyramine, also 14 Enterococcus isolates were hemolytic. Non of Lactobacillus isolates were able to produce biogenic amines or express hemolytic activity.Cell autolyis rates of selected LAB cultures: Cell autolysis rates increased by increasing the concentrations of NaCl and the incubation time. Cell autolysis rates of the Lactobacillus spp. isolates number 2 and 4 were higher than the cell autolysis rates of Ent. faecalis isolate number 2 and the Lactobacillus plantarum isolate number1.The effect of using selected LAB adjuncts on the sensory properties and chemical composition of Domiatti cheese: results showed that the sensory properties and the chemical composition of the resultant cheese affected by both the culture species and strain, and the form in which it will be added during cheese making CONCLUSION In conclusion, using of the freeze-shocked attenuated culture of Enterococcus faecalis isolate number 2, and the viable cultures of both Lactobacillus spp. isolates number 2 and 4 as adjunct cultures during the preparation of Domiatti cheese from pasteurized milk could improve the sensory properties of the resultant cheese.