الفهرس 
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Abstract
bacteria
Lactic acid bacteria (LAB) are groups of related bacteria that produce lactic acid as a
result of carbohydrate fermentation (Arimah et al., 2014). LAB possess some common
morphological, metabolic and physiological characteristics (Sahnouni et al., 2012). The
general description of the bacteria included in the group is Gram-positive, non-sporulating,
catalase negative, rods and cocci (Ibourahema et al., 2008). Due to their lack of
pathogenicity, most LAB are generally recognized as safe (GRAS) organisms (Mahantesh
et al., 2010).
1.1.1. Distribution
LAB are widely distributed in different ecosystems and are found in many dairy
products, fermented meats, vegetables, sourdough, silage, beverages, sewage, plants and
also in the genital, gastro intestinal (GI) and respiratory tracts of man and animals
(Savadogo et al., 2006). LAB are closely associated with the human environment, as they
are used for the production of a wide variety of fermented food products, in which they
contribute to the improvement of flavor, texture and shelf-life. They also help in keeping
microbial quality by producing antimicrobial substances in dairy products (Sahnouni et
al., 2012).They have complex nutritional requirements for amino acids, peptides,
nucleotide bases, vitamins, minerals, fatty acids and carbohydrates, and may grow under
anaerobic and aerobic conditions (Khalid 2011). LAB are mesophilic with optimal
temperature of growth between 30°C and 40 °C and optimum pH of 5.5-5.8 (Kocková et
al., 2011).
1.1.2. Dairy products
Dairy products are foods rich in many nutrients that may be enhancing health and
beneficial in preventing different diseases. In terms of health they play a role in promoting
normal growth and healthy bones and teeth (Mahmoud et al., 2008). For diseases it has
been known to lower blood pressure and reduce the risk of high blood pressure,
particularly when included as part of a dietary pattern that is low in fat and rich in fruits
and vegetables (Reusser and McCarran 1994).
Dairy products are sources of at least four different minerals/electrolytes (calcium,
sodium, potassium and magnesium) (Mahmoud et al., 2008). Recently, a number of novel
fermented dairy products and infant milk powder have been developed and are being
marketed under the name of probiotic products (Dardir 2012). Probiotic cultures have
been associated historically with cultures of milks and dairy products, from which there is
substantial evidence for positive effects on human health and general well-being
(Nowroozi et al., 2004).
Egyptian dairy products such as Karish cheese (skimmed milk cheese, Mish (pickled
ripened Karish cheese), Zabady (yogurt) and Laban Rayeb (concentrated sour milk) are a
good valuable sources of LAB bacteria with new important industrial properties and
genetic biodiversity (Mabrouk et al.