الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The objectives of this study were mainly directed to isolate and molecularly identify some lactic acid bacterial strains from milk and some Egyptian dairy products, and to study their
ability to produce proteolytic activities to obtain bioactive peptides with antimicrobial, antidiabetic, and antioxidant activities. These identified bioactive strains were evaluated for
technological and safety standards and used in the production of high-quality and healthy Karish cheese. The study was divided into 3 parts:
Part 1: Isolation and identification of lactic acid bacterial strains:
a) Primary isolation of lactic acid bacteria strains:
One hundred and sixty-six different samples of Egyptian dairy products were collected from ten different Egyptian governorates, including buffalo, cow, sheep, camel milk, Karish, Domiati, Ras, and mish cheeses. These samples were collected. It was possible to
isolate 634 isolates that were probable lactic acid bacteria.
b) Screening of Lactic Acid Bacteria for proteolytic activity:
The results indicated that 179 out of 634 isolates had proteolytic activity, and 455 isolates were negative in terms of proteolytic activity.
c) Screening of Lactic Acid Bacterial strains with proteolytic activity according to some technological criteria:
One hundred and seventy-nine Isolates were subjected to some technological standards
such as acid production and production of exopolysaccharides, in addition to their
proteolytic activity. The results indicated that 39 out of 179 isolates had the highest
proteolytic activity, and 32 strains had a high ability to produce acid. Based on these two
traits, eight isolates were selected to undergo the sequencing strategy.
d) Molecular identification of the selected strains:
The eight isolates were identified by sequencing method using the 16S rDNA gene and it
was found that the isolates belong to the following species (or subspecies):
Lactobacillus rhamnosus (FFNL1308), Lactococcus lactis (FFNL1940), Lactococcus
lactis (FFNL1969), Lactococcus lactis subsp. lactis bv diacetylactis (FFNL2005),
Pediococcus acidilactici (FFNL2062), Lactococcus lactis subsp. lactis (FFNL4041),
Lactiplantibacillus plantarum (FFNL4621) and Weissella confusa (FFNL4939).
Part 2: Antimicrobial Activity, Assessment of Biological Activity (In vitro),
and Safety Traits of Identified LAB Strains:
a) Factors affecting antimicrobial activity:
Most of the eight isolates showed full or partial antimicrobial activity for the following seven
pathogens: Escherichia coli ATCC 8739, and ATCC 23235, Salmonella Typhimurium ATCC
14028, Pseudomonas aeruginosa ATCC 9027, Staphylococcus aureus ATCC 6538, and Candida
albicanis ATCC 10231, Listeria monocytogenes ATCC 679 and Bacillus cereus ATCC 10987.
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Some factors were studied in the antimicrobial activity of isolates such as heat treatment, pH,
and the effect of proteolytic enzymes. The results indicated that the cell-free extract of isolates
can withstand completely or partially in front of the used heat treatments, pH values , and the
proteolytic enzymes used.
b) Evaluation of biological activity (anti-diabetic activity and anti-oxidant activity):
The cell-free extract of isolates was found to have anti-diabetic activity by inhibiting the αamylase enzyme. Inhibition rates ranged between 2.48 - 97.38%.
It was also found that the extract of cell-free isolates has anti-oxidant activity, and DPPH was
used, which reached a percentage of antioxidant activity between 7.42-23.90%. ABTS was
used, and the percentage of antioxidant activity ranged between 14.45-73.61%. The
substance FRAP was also used, and the values of the antioxidant activity ranged between
79.78 and 359.12.
c) Safety standards for isolates of lactic acid bacteria that have been identified:
The eight isolates were tested for sensitivity to 14 types of antibiotics. The results indicated
that the isolates varied in terms of resistance and sensitivity. It was found that the strain Lb.
plantarum FFNL4621 is sensitive to 12 antibiotics and resistant to 2, while the strain Lc.
Lactis FFNL1940 and the strain W. confusa were sensitive to 9 and resistant to 5 antibiotics.
Other safety features have been used such as hydrolysis of gelatin, DNA, or hemolysis, as
well as the ability to produce amines (histamine). The results indicated that all eight strains
did not show any ability to hydrolyze gelatin and DNA. And they weren’t able to produce histamine.