الفهرس 
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Abstract
One hundred street vended raw milk and ninety white soft cheese samples were collected from Alexandria province. The samples were obtained as sold to the public and transferred to the laboratory to be examined.7.1. Organoleptic evaluation for street vended raw milk and white soft cheese samples.All samples were sensory evaluated for flavor, texture, and appearance before being subjected to the chemical and microbiological examinations to ensure that the collected samples were apparently fit for human consumption.7. 2. Storch’s test for detection of heat treatment in raw milk:- All raw milk samples were tested for heat treatment. All samples developed indigo blue color was raw.7.3. Quality Evaluation:< 7.3.1. Determination of titratable acidity and pH value of raw milk and soft white cheese:- The mean value of titratable acidity percent in the examined street vended raw milk samples was 0.137± 0.008. The mean value of pH of the street vended raw milk samples was 6.64 ± 0.02. While in soft cheese samples the titratable acidity was of mean value 2.41±0.01, and the mean value of pH was 4.60±0.07. 7.3. 2.Methylene blue reduction test for raw milk:- The mean value of Methylene blue reduction time (min) for street vended raw milk samples was 56.75 ± 18.25. Moreover, 44% of the examined raw milk samples were above the standard of 4.5 hrs. stipulated by (ES 2005-154). There were 15% of examined street vended raw milk samples had grade I (good quality), while, 60% of examined samples had grade II (fair quality). Also, 16% of examined raw milk samples had grade III (bad quality) and the rest of the samples which represent 9% were very bad quality as they reduced the methylene blue color in less than 20 min. 7.4. Bacteriological evaluation: 7.4.1. Enumeration of Coliforms in raw milk and white soft cheese samples:- The incidence of Coliforms in examined Street–vended raw milk samples was 80% and the mean value was 2.4x106±1.2x106. In soft cheese samples the incidence were 32.2% mean value 3.3x105 ± 1.8x105.All these samples are not complying with (ES, 2005-154) which require the samples to have not more than 10 cell/ml or gr . 7.4.2. Enumeration of Clostridia organisms in raw milk and white soft cheese samples: The incidence of Clostridium spores in examined street–vended raw milk was 40% with mean value 9.11x102 ± 4.8x102. While in white soft cheese the incidence of Clostridium spores were higher, it was 42.2% with mean 3.3x102 ± 0.15x102. 7.4.3. Enumeration and Isolation of Bacillus cereus in raw milk and white soft cheese: The incidence of Bacillus cereus in raw milk samples was 55 positive samples from 100 examined raw milk sample, the mean value was 3.13x102 ±0.64x102. While in white soft cheese samples the incidence were less than in raw milk samples only 16.7% 0f the examined samples were positive with mean value of 8.8x10 ± 0.4x10. All these samples are not complying with (ES, 2005-154) which require the samples to have not more than 1 cell/ml or g. 7.4.4 Frequency distribution of isolated Bacillus species from examined raw milk and white soft cheese samples by Microbial genotyping/ Vitek®2 compact:- By analyzing the isolates by Vitek®2 compact technique the obtained results were Bacillus cereus , Bacillus badius, Bacillus farraginis, Bacillus .licheniformis were found in raw milk in percentage of (56.4,12.8,7.7, 23.1%) respectively . While Bacillus cereus, Bacillus badius, Bacillus farraginis, B.licheniformis were found in in white soft cheese with percentages (61.9, 14.3, 9.5, and 14.3 %) respectively. 7.4.5. Enumeration and isolation Clostridium perfringens in examined raw milk and soft cheese samples:- The Incidence of Clostridium perfringens in street–vended milk was 33% with mean value 9.1 x 10 ±0.01x10. While in soft cheese its Incidence was 12.22% with mean value 2.2 x 102 ± 0.02x102. All these samples are not complying with (ES, 2005-154) which require the samples to have not more than 1 cell/ml or g. 7.4.6. Enumeration and isolation E. coli O157: H7 in raw milk and soft cheese samples:- A total of 100 raw milk samples and 90 white soft cheese samples were assayed for E. coli O157:H7. The organism was not found in any samples of white soft cheese and only 5% of the raw milk samples. E. coli O157:H7 was implanted on different medium. So suspected colonies (non–sorbitol fermenting, colorless colonies) on Sorbitol MacConkey II Agar with Cefixime and Tellurite were 5% 0f the samples and when picked and cultivated on Tryptone Bile x-glucuronide (TBX) medium which is chromogenic media E. coli O157:H7 can grow on it as white colonies only three samples were positive , after that the isolates were analyzed by Vitek®2 compact method but the result serotype them as E.Coli . 7.4. Experimental study (Studying the effect of different concentrations of Nisin (4, 8, 12 ppm) and different salt concentrations (1, 3, 5%) on the isolated gram positive pathogenic organisms (Bacillus cereus and clostridium perfringens) :- So 50 kg of pasteurized milk were manufactured in the Labe each 5 Kg were separately treated with different percentage of salt (Na Cl) 1, 3, 5 %. Each salt concentration will repeated three times with different Nisin concentrations 4, 8, 12 ppm /kg milk. Also 1ml of each Bacillus cereus and Clostridium perfringens Tryptic soy broth containing 0.6% yeast extract (TSBY) were also inoculated in each separate one. The initial count was 2 x104 cell/ ml for B.Cereus, and. 5 x103 cells/ ml for C.Perfringens. The most agreeable effect of Nisin with combination of the highest level of salt which was 5%. Even with only 4ppm of Nisin the count decreased from 67.66x102 ±2 x102 to 1.1 x10 ± 0.2 x10 at the third week of storage. The best effect of Nisin on the growth and multiplication of Bacillus cereus was at 12ppm combined with 5% salt concentration. Best results were recorded as the combination of 5% salt with different concentration of Nisin give gradual effect on growth and multiplication of Clostridium perfringens as sharp decrease in the level of Clostridium perfringens from 99.6 x10 ±1.5 x10 to 1.3 x10 ± 0.3 x10 with 4ppm Nisin at the end of the third week while it decreased to 8.0 x10 ± 0.3 x 10 with 8ppm Nisin at the end of the second week and disappeared at the end of third week. So as we actually isolated Bacillus cereus and Clostridium perfringens from white soft cheese sold at local markets with the previously mentioned percentages, we can insure the importance of preservative addition to these traditional white soft cheeses to insure the safety of the consumers.