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Abstract
Two hundred and fifty samples of raw milk (100), kareish cheese (75) and ice cream (75) were collected from supermarkets and street vendors at Alexandria province. The samples were obtained as sold to the public and transferred as soon as possible to the laboratory to be examined. All samples were examined organoleptically before being subjected to some chemical and microbiological examinations to ensure that the samples were apparently fit for consumption.
The results can be summarized as follows:
1. Compositional quality tests:
1.1. Raw milk:
• Acidity percent: The mean value of acidity percent was 0.15 ± 0.003. 34 (34%) were proved to be above standards.
• pH value: The mean value was 6.36 ± 0.01.
• Methylene blue reduction test: There were 18% of samples of grade I, 70% of grade II, and 12% of grade III.
1.2. Kareish cheese:
• Acidity percent: The mean values of acidity percent in Kareish cheese samples were 1.82 ± 0.008.
• pH value: The mean values were 4.70 ± 0.043.
• Sodium chloride content: The mean values was 3.62 ± 0.176. All examined samples were complied with Egyptian Standards.
1.3. Ice cream:
• Methylene blue reduction test: There were 32% of samples of grade I, 33.34% of grade II, 28% of grade III, and 6.66% of grade IV.
2. Bacteriological examination:
2.1. Isolation of Listeria species:
• The incidences of Listeria species in the examined raw milk, kareish cheese and ice cream samples were 3 ; 2.66 and 2.66 %, respectively.
2.2. Identification of Listeria species:
• The incidences of Listeria monocytogenes in the examined raw milk, kareish cheese and ice cream samples were 3 ; 2.66 and 2.66 %, respectively.
• All examined positive samples were not complied with Egyptian Standards.
• The incidences of Listeria innocua in the examined raw milk, kareish cheese and ice cream samples were 0 ; 0 and 1.33 %, respectively.
• The incidences of Listeria murrayi in the examined raw milk, kareish cheese and ice cream samples were 1 ; 1.33 and 0 %, respectively.
2.3. Serological identification of isolated Listeria monocytogenes:
• The isolated serotypes of Listeria monocytogenes from the examined raw milk samples were 2 (66.66%) belong to serotype I, while the third isolate was untypable.
• The isolated serotypes of Listeria monocytogenes from the examined kareish cheese samples were 1 (50%) belong to serotype I, while the second isolate was untypable (50%).
• The isolated serotypes of Listeria monocytogenes from the examined ice cream samples were 1 (50%) belong to serotype I, while the second isolate was untypable (50%).
2.4. Identification of isolated Listeria monocytogenes by PCR technique:
• All Listeria monocytogenes serotype I possess the virulence gene (Listeriolysin O) isolated from examined raw milk, kareish cheeses and ice cream samples.