الفهرس 
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Abstract
The objectives of this study were to isolate, identify and enumerate the stormy fermenter Clostridia species in the examined samples, to study the public health and economic importance of the isolated organisms, as well as to study the inhibitory effect of potassium sorbate on C. Perfringens in freshly manufactured soft cheese. A total one hundred random samples of milk and milk products including raw milk, milk powder, baby food, processed cheese and Rass cheese (20 samples each) were collected from Mansoura city markets to be examined. Results revealed that the incidence of stormy fermenter Clostridia species was 15%, 40%, 50%, 75% and 30% in raw milk, milk powder, baby food, processed cheese and Rass cheese samples respectively. Regarding to raw milk samples, Clostridium perfringens was the only Clostridia isolated from the examined samples with a count ranged from 21 to 70/ml raw milk. While, Clostridium perfringens and C.butyricum were isolated from 75% and 25% of the examined milk powder samples respectively and the Clostridial count ranged from 8 to 40/ml reconstituted milk powder. In baby food, Clostridium perfringens and C.butyricum were isolated from 70% and 30% of the examined samples respectively where the count ranged from 9 to 40/ml reconstituted baby food. In processed cheese, Clostridium perfringens, C.butyricum, C.septicum and C. chauvoei were isolated from (46.7%, 33.3%, 13.3% and 6.7%) of examined processed cheese samples respectively and the Clostridial count ranged from 9 to 40/g processed cheese while in Rass cheese, The isolated Clostridia were identified as C.perfringens (49.9%), C.butyricum (16.7%), C.septicum (16.7%) and C.sphenoides (16.7%) and the Clostridial count ranged from 6 to 23 /g Rass cheese. By studying the inhibitory effect of potassium sorbate on Clostridia in freshly manufactured soft cheese, the results revealed that on using 2g of potassium sorbate/l UHT milk, the inoculum size was decreased from 5x106/ml UHT milk to 3x103/g cheese with 99.94 percent of reduction after 8 days, but the previous reduction percent was obtained after 2 days on using 3g of potassium sorbate/l UHT milk.. So it is more applicable to add the sorbates in a level of 0.3% rather than 0.2%.