الفهرس 
Introduction
Raw milkOnly 14 pages are availabe for public view
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Abstract
A total of 120 samples of milk were collected from the Unite of Dairy Technology, Faculty of Agriculture, Assiut University. The samples were divided as:
30 samples of raw milk before pasteurization,
30 samples of pasteurized milk directly after pasteurization
60 samples from the second day and third day of storage at refrigeration temperature (30 of each).
Raw milk undergoes flash pasteurization (cooling, heating and homogenized at 83 ºC for 5 second followed by cooling to 5 ºC). Pasteurized milk was aseptically filled in plastic bags of half a kilo.
All pasteurized milk samples were examined chemically using phosphatase test and they were phosphatase test negative. The microbiological examinations include:
- Total bacterial count and Thermoduric count
- Psychrotrophic count and Thermoduric psychrotrophs
- Thermophilic count
- Coliforms, Fecal coliforms and E. Coli
- Enterococci count - Anaerobes
- Total yeasts and molds count.
The average values were summarized in the following table:
Microbiological examinations Average values of microorganisms (cfu/ml)
Raw milk Pasteurized milk
0 day of validation 2nd day of validation 3rd day of validation
TBC(Thermoduric count) 3.7×106 1.5×103 2.4×103 5.4×104
Psychotrophic count(Themoduric psychrotrophs) 2×106 3×102 9×102 3×103
Thermophilic count 7×10 6×10 6×10 6×10
Enterococci count 5×104 4×102 1×103 6×103
Total yeasts and molds count 1×104 1×102 1×102 2×102
The percentages of coliforms, fecal coliforms were 100% in the examined samples. 76.6 and 70 % of samples had count more than103 respectively. E. coli detected in 73.3% in the samples. After pasteurization, the percentage of coliforms, fecal coliforms and E. coli decreased to 40, 26.6 and 0%, respectively.
The prevalence of anaerobes in the examined raw milk samples were 86.7%, this percentage followed descending to 50% after pasteurization then increased to 70, 80% in the second and third day after pasteurization, respectively.
All raw milk samples count exceeded the Egyptian and Europian standards for TBC, coliforms, Enterococci counts. Regarding E. coli contamination, only 8 raw milk samples are acceptable while, all pasteurized milk samples met the standards. Regarding E. coli contamination, only 8 raw milk samples are acceptable and all pasteurized milk samples are acceptable.
The analysis of variance (ANOVA) showed highly significant differences (**P< 0.01) between raw and pasteurized milk through the three days of shelf life period for all bacterial quality parameters except thermophils. Examination of thermophilic count for raw and pasteurized milk samples collected daily indicated that there was no significant (P > 0.05) difference in the thermophilic counts between raw and pasteurized milk during 3 d holding periods. However, during storage period significant increase (*P<0.05) in the total bacterial count and psychrotrophic count was noticed between the pasteurized milk at the 1st and 3rd days of validation. Also, the results indicated that the bacterial numbers of thermoduric, Enterococci and total yeasts and molds of pasteurized milk samples did not differ significantly (P > 0.05) during 3 days holding periods in milk samples relative to numbers present on initial day. The results show that in most instances, any change in counts in milk stored in refrigerator at 4°C for up to 3 days is small relative to their initial counts.
Finally, the germs content in raw milk is of great interest for the preparation of pasteurized milk. Indeed, the number of heat-resisting in raw milk influences not only their content in pasteurized milk, but also its preservation duration in case of no recontamination germs after pasteurization. Moreover, the shelf life of pasteurized milk can be extended by introducing better hygienic transfer from processing to filling machines and the filling process factors that limit the stability of milk are well established including bacterial contamination, inadequate package system and improper temperature control.