الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
SUMMARY AND CONCLUSION
Lactic acid bacteria (LAB) are used as starter cultures for the production of fermented dairy products and that occur naturally as indigenous microbiota of raw milk. The new incredulously demand of customers for natural safe products and the potential health hazards of chemically preserved and processed products have led to the advent of alternative technologies using LAB as starter cultures for the production for the preservation of intended food matrixes.
In the present study was designed as a trial for the sweet whey low-cost by-products as a medium for the growth of LAB as bio-preservative starter cultures for the production of fermented dairy products.
The results of this study can be summarized as follows:
1- A total number of 32 isolates were isolated from raw cow and goat milk and cottage cheese using the specific De- Man, Regosa, Sharp (MRS). All isolates were rod shaped, Gram-positive, non-motile, non-sporeformers and catalase negative, hence could be were identified as members of the genus Lactobacillus.
2- The isolates showed positive results in their growth on the sweet whey medium by comparison with the specific medium. The ability of these isolates to produce inhibitory substances for seven pathogenic bacteria was tested by using the disk diffusion method. The isolates gave positive results in inhibiting the growth of pathogenic bacteria compared to their growth on the specific medium of lactic acid bacteria.
3- Cell free supernatants (CFS) varied in their antibacterial activities against of seven foodborne organisms and pathogens using the disc diffusion assay. Twenty-four isolates were active against seven indicators (75.0%), 5 isolates antagonized 5-6 indicators (15.6%) and 3 isolates showed mild activities antagonizing activities (9.4%). Most Lactobacillus isolates (84-100%) inhibited the growth of both Gram-positive and Gram-negative pathogens tested.
4-When the CFSs of Lactobacillus isolates were adjusted to pH 7.0 , the antibacterial activity disappeared but when treated with catalase, the antibacterial activity did not affect. These active isolates were good acid producers causing a DROP in pH of supernatants between 3.7 and 4.9, but activities completely disappeared by neutralization. In addition inhibition due to hydrogen peroxide was excluded because no sensitivity to catalase was detected. Therefore, antibacterial activity could be attributed mainly to organic acids production.
5- Twenty-four of Lactobacillus isolates antagonizing the seven tested pathogens were subjected to HTST pasteurization treatment (72ºC/15sec). Of these, only five isolates showed high residual activities, i.e., K5, K6, G9, C3, and C7.
6-The isolate C7 showed the relatively highest residual activity and was completely identified as Lactobacillus brevis 200217-029 by 16s DNA gene.
7- By analyzing of metabolites have been produced by this strain Lactobacillus brevis 200217-029, were a group of organic acids ( lactic acid, butyric acid, propionic acid, citric acid, formic acid and sorbic acid ), additionally gas production. Therefore, this strain described as a hetero fermentative.
8- Antibacterial activity of Lactobacillus brevis 200217-029 was found stable at 40º to 100ºC for 30 min, was found stable in pH range of 2.0 to 4.0 and was grown in the presence of salt up to 6.5% NaCl and its antibacterial activity was stable up to 6.5% NaCl but it was lost in the presence of acetone and Ethylene di-amine tetra acetic acid (EDTA).
9- Best conditions for mass production of this Lactobacillus brevis 200217-029 could be achieved by growing at pH 7.75 and 25ºC with inoculum size 7.5% at salt concentration of 5.25% NaCl and incubated for 72 hours.
10- Therefore, the growth of Lactobacillus brevis 200217-029 on the sweet whey low-cost by-product will certainly reduce production on the industrial scale. The aforementioned characteristics of this Lactobacillus brevis 200217-029 together with its strong antibacterial activity against of G+ve and G-ve pathogens recommended its use as bio-preservative for fermented dairy products which are subjected to harsh heat treatment and could be functional for the production of some cheese which contain relatively high salt concentration.