الفهرس 
Karish cheeseOnly 14 pages are availabe for public view
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Abstract
Karish cheese is the most popular Egyptian soft low fat cheese, it is made mainly from raw milk without adding starter cultures. The fermentation occurs as a result of the flora present in the raw milk and in the surrounding environment, therefore, taste and texture of the cheese vary too much. The natural flora present in raw milk may contain undesirable microorganisms which cause a lot of defects in cheese. So, the Egyptian Organization for Standardization and Quality Control (Egyptian Standards, 2001; 2005) recommended the pasteurization of cheese milk and consequently use of proper starter culture.
The aim of this investigation was to isolate lactic acid bacteria from traditional Karish cheese and identify them using phenotypic and genotypic methods and to study the technological characteristics of the identified strains. Then select promising strains to improve the manufacture of Karish cheese made with pasteurized milk. Safety of some selected enterococci strains was in vivo investigated.
To fulfill this aim, 15 samples of traditional Karish cheese were collected from markets at EL Asafra; Zananeary; Sedi Gaber; Camp Czar; Janekils at Alexandria city.
The above aim was achieved by:
1. Isolation and identification of the natural LAB of different traditional Karish cheese samples using phenotypic and genotypic methods.
2. Study the technological properties of some identified strains.
3. Study in vivo the safety of some selected strains.
4. Some selected strains were applied to improve Karish cheese, the chemical, microbilogical, rheological properties and sensory evaluation of the produced Karish cheese were studied.
The obtained results revealed the following:
1. A total of 89 isolates of Gram positive and catalase negative of non starter lactic acid bacteria were isolated from 15 samples of Karish cheese.
2. Percentages of facultative heterofermintative lactobacilli isolates (group B), obligatory heterofermintative (group C) and obligatory homofermentative lactobacilli isolates (group A), were 51.35, 37.83 and 10.82, respectively.
3. Lactobacillus spp. isolates were found in high proportion (41.57%) followed by Enterococcus spp. (37.07%) and Lactococcus spp. (12.35%). Whereas Streptococcus thermophilus and Leuconostoc spp. were found in equal minor proportion (4.49%).
4. Eighty nine isolated strains were screened for their flavour forming ability and acid production in milk culture.
5. Twenty six selected isolates were identified using the fermentation of carbohydrates. E. faecium was more common (34.62%) between isolates of Karish cheese samples followed by E. faecalis (23.08%). Wheras equal propotion (7.69%) of Lactocaccus lactis subsp lactis, Lactococcus lactis subsp cremoris and Lb. delbruekii. subsp lactis were found. Lb. delbruekii. subsp del., Lb. casei, Lb. plantarum, Lb. fermintum and Lb. brevies each constitutes small proportion (3.85%) of the isolates.
6. Five selected strains were further identified by genotypic characteristics using 16s rRNA technique, they were confirmed as E. faecium KT712, Lb. del. subsp lactis KP654, L.lactis subsp cremoris KM746, Lb. plantarum KP623 and L. lactis subsp lactis KM721.
7. Technological properties of selected strains were varied.
8. Autolytic activity of lactobacilli strains were higher than that of enterococci and lactococci strains.
9. The highest rate of autolytic activity was shown in Lb.del.subsp lactis KP645 (52.3%) followed by Lb. brevies KP653 (47.36%) and E. feacium KM742 (44%).
10. Most isolated strains showed a slow rate of acidification, they didn’t reach Δ pH of 0.4 after 5 h.
11. Lactococcus lactis subsp lactis KM721 was found to produce EPS.
12. Six strains of Lactobacillus spp. (Lb. fermintum, Lb. plantarum, Lb. casei, 2 strains of Lb.del.subsp lactis and Lb. brevies) and one strain of each E. faecalis, E. faecium exhibited antagonistic activity.
13. E. faecium KT712, Lb. delbruekii subsp lactis KP654, L. lactis subsp cremoris KM746, Lb. plantarum KP623 and L. lactis subsp lactis KM72 strains were selected according to their technological properties to improve Karish cheese quality.
14. The in vivo experiment showed that E. feacium KT712 was safe for human use.
15. General chemical composition of different cheese treatments were slightly different, but they were similar to that of conventional Karish cheese.
16. All cheese samples were sensory evaluated as typical of Karish cheese.
17. Lactococcus lactis subsp lactis (EPS producer) had positive effect on texture profil and organolyptic properties of Karish cheese (T3, T7).
18. The mixed culture of selected strains; Lb plantarum (KP623) and L. lactis subsp lactis (KM721) T7 or E. faecium (KT712), Lb. del. subsp. lactis (KT654) and Lactococcus Lactis subsp cremoris (KM746), T8 had a positive impact on rheological and sensorial properties of the resultant Karish cheese.