الفهرس 
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Abstract
Yeast constitutes a large and heterogeneous group of microorganisms that are currently attracting increased attention from scientists and industry. Yeast have been established as proficient producers of secondary metabolites that exhibit various biological activities. Sixty nine yeast were isolated from different 17 natural food sources to screen these isolates for some biological activities, and identification of the promising isolates. Vitro screening showed that 70%of the 69 isolates inhibited growth of bacteria, No antibacterial activity of 7 adjusted crude cells - free Yeast isolate supernatants (CCFYIs) to pH 6.5 was recorded toward all indicator bacteria, No inhibitory effect of two isolate after treated (CCFYIs) with catalase, The obtained data revealed that the Clostridium butyricum and Clostridium tyrobutyricum were more sensitive to the supernatant of isolates no Eg-Y2 and Eg-Y20.The antibacterial activities (AAs) of 21 yeast isolates were compared with those of 16 antibiotics using E. coli, L. monocytogenes and S. enteritidis as indicators, Results showed, that some yeast isolates exhibited higher AAs than that of some antibiotics. Thirteen yeast isolates showed best performing were chosen for antifungal activity, all of these isolates exhibited antifungal activity against one or more of the 5 indicator fungi. The thirteen isolates were tested for their ability to produce volatile metabolites and their effect on fungi. All isolates released volatile metabolites which strongly inhibited growth of fungi. In vitro screening of (CCFYIs) for anti-cancer activity out of 13 yeast isolates, 8 inhibited crown gall tumors formation on potato discs while 5 showed doubtful results.
Identification of the chosen 13 isolates suggest that these isolates were Candida pelliculosa, Cryptococcus neoformans, Candida guillermondii, Candida glabrata, Candida famata and Rodo. muciluginosa
Eg-Y2 isolate (Candida pelliculosa) screened for Inhibition of processed cheese –late gas using its dried supernatant at different concentrations (1, 3 and 5 mg/g cheese)compared with nisin(1000 IU/g). The chemical, physical and microbiological analyses of the resultant cheeses were performed at zero, 1, 2 and 3 months of storage. The results showed that the addition of 5 mg/g of dried supernatant of Candida pelliculosa yeast (DSOCY) during processed cheese spread manufacture prevented of late-blowing in cheese manufacture.