LAB are well known as starter cultures in the manufacture of dairy products, such as acidophilus milk, yogurt, buttermilk, cottage cheeses, hard cheeses and soft cheeses. LAB have a GRAS status, and approximately 60% of the diet in many developing countries consists of fermented foods (Stiles, 1996). The addition of L. casei AST18 did not affect the sensory quality of the yogurt and increased the number of viable cells in the yogurt samples. The use of L. casei AST18 as a biocontrol agent inhibited the growth of corrupting fungi in the yogurt. Schnurer and Magnusson (2005) revealed that three mechanisms may explain the antifungal and antimicrobial efficiency of LAB: the yield of organic acid, competition for nutrients and production of antagonistic compounds. The antifungal compounds isolated from LAB fermentation cultures
are mainly low-molecular mass metabolites these compounds are lactic acids, acetic acid, phenyllactic acid propionic acid, proteinaceous and cyclic dipeptide Lactic acid and cyclo-(Leu-Pro) are the antifungal compounds identified in L. casei AST18