الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 120 |  |  |
| | | from | 120 | | |
Abstract
Naturally fermented milk products are very fantastically in taste and flavor .So, these products play an important role in the diets of many people in the world.
Dairy products are an important source and one of the most common carrier for probiotic bacteria. At present, much attention has been made to use lactic starters for their potential probiotic characteristics .It is of interest to study some factors that affect the growth and survival of probiotic bacteria while in transit in dairy products to human use.
So, this work aimed to investigate the tolerance of some probiotic bacteria tocertain adverse conditions (i.e. high acidity, bile salts and NaCl). Moreover, the adhesion of the probiotic bacteria to columnar epithelial cells of the small intestine of sheep and antagonism activity were also studied . To study these factors, local bacterial isolates were compared to strains belonging to three genera (Bifidobacterium, Streptococcus and Lactobacillus), to their future application in the manufacture of bio-yoghurt as a functional food .
Forty eight isolates were isolated from (ras , kariesh cheese and whey ) from local market in Minia governrate, using MRS media for and identification was carried out using morphological, physiological tests.
1- Isolation of LAB from dairy products:
The results showed that:
- out of 48 isolates, 39 bacterial isolates were found to be Gram positive and catalase negative,that mean ( 39 isolates) are lactic acid bacteria .
- These 39 isolates were selected and subjected to further tests and unsuitable isolates were discarded
2- Screening for probiotic creteria :
The obtained results showed that
- of the selected isolates exhibited low acid tolerance with exception of two isolates Wh1 and Wh5 which showed growth increase of 4 and 5 folds, respectively.
- In order to evaluate these two isolates (Wh1 and Wh5), seven reference strains were tested at the same conditions all of them showed higher acid tolerance to pH4 and their growth increase ranged from 3.3 to 5.3 5 folds
- In respect of bile salt tolerance after 48 hrs, the highest growth values (optical density) were found to be 2.905 and 2.623 for isolates L1 and wh5, respectively. Whereas, the highest growth increase values were found to be 8.584 folds and 6.572 folds for isolates wh5 and B2, respectively.
- The adherence of the nine strains to sheep epithelial cells indicated that all stains have the ability to adhere to epithelial cells .
- Among the 9 tested isolates, 3 were found to be highly NaCl tolerant (B1 ,B4 and wh5) with optical density ranging from 6.03 to 6.28.
- All of the strains showed antimicrobial activity against Gram positive and Gram negative pathogenic bacteria ( Staphylococcus aureus , Escherichia coli and listeria meningitis).
- None of the strains showed any inhibitory effect to Salmonella typhimurium.
-The inhibition zone diameters ranging from 28 to 70 mm.
Yoghurt Production:
- both of the two isolates (Wh1 and Wh5) exhibited decrease in the milk pH during 24 hrs from 6.7 to 4.4
-The initial acidity ranged between 0.65 to 0.74
-While at the end of storage period reached at the highest value 0.99 % in (Y S) +Wh5 . while the treatment (Y S) +Wh1 had low acidity as the control.
- the curd tension (C.T.) was higher for all treatments of the isolates mixed with Y.S. (23.8 – 31.2 gm) than the control 19.3 gm, and the highest value was recorded for Y.S +wh5. treatment.
- A noticeable decline in curd tension then occurred in C.T. in treatments and the control till the 2nd week of storage.
-During storage, the bacterial counts increased remarkably (one cycle) in the 3rd day, followed by an slight decline in the 7th day.
- In this study all of the manufactured yoghurt still contain more than 107 cfu per ml until the end of storage period .
- Only the isolate wh1 had antagonistic reactions against Lactobacillus bulgaricus
In conclusion, this study revealed that dairy products are important sources of probiotic bacteria. In this study lactic acid bacterial isolates (wh1 and Wh5) were isolated from dairy products, e.g. Ras cheese, whey and other fermented dairy products and were found to have probiotic properties. Therefore, these isolates exhibited promising results in production of functional food.
Further studies should be carried out to complete the identification of the selected probiotic isolates which can be used to produce dairy products of high quality.