الفهرس 
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Abstract
One hundred random samples, fifty of natural yoghurt (plain) and 25 each of fruit yoghurt (strawberry) and flavored yoghurt (honey) were collected from different dairy shops and markets in Sharkia Governorate, Egypt. The collected samples were examined physically (sensory evaluation), sanitary (determination of titratable acidity), and bacteriologically.
It’s evident from the obtained results that the highest frequency distribution of examined yoghurt samples based on suggested score for sensory evaluation was (44%) of examined natural (plain) yoghurt samples and lies within the range of 93-100%, while were (72%) of examined fruit yoghurt (strawberry) samples and (88%) of examined flavored yoghurt (honey) and lies within the same range .
It’s evident from the obtained results that the acidity% in natural yoghurt (plain) samples, fruit yoghurt (strawberry) samples was 0.83% and 0.90%, respectively, while in case of flavored yoghurt (honey) samples was 1.06%.
The obtained results revealed that the mean coliform count/g. in examined yoghurt samples was 4.6x 104± 2.2x104 and 4.7x 103 ±3.0x103 for natural yoghurt (plain) and fruit yoghurt (strawberry), respectively, while, Coliform organisms in examined flavored yoghurt (honey) recorded 3.6x102 + 3.5x102. The most prevalent coliform species isolated from examined natural yoghurt (plain) and fruit yoghurt (strawberry) samples were Citrobacter freundii, K. oxytoca and Enterobacter agglomerans by percentages of (20%, 18% and 14%) and (12%, 8% and 16%), respectively, while in examined flavored yoghurt (honey) samples the most prevalent coliform species are Citrobacter freundii and Enterobacter agglomerans by percentages of 24.0% and 4.0%, respectively.
The mean staphylococci count/g in examined natural yoghurt (plain) and fruit yoghurt (strawberry) was 1.7x 104 ± 1.1x104, 5.2x 102 ± 3.3x102 respectively, but in case of flavored yoghurt (honey) it was 2.8x 102 ± 2.7x102. Staphylococcus aureus and Staphyloccus epidermidis were the predominated Staphylococci isolated from the examined natural yoghurt (plain) and fruit yoghurt (strawberry) and flavored yoghurt (honey) samples in percentages of (12% and 6%), (12% and 4%) and (4% and 4%), respectively.
Salmonelle failed to be detected in examined samples.
Yersinia spp. could be detected in (16%) out of examined fruit yoghurt (strawberry) samples, while they couldn’t be detected in both examined natural yoghurt (plain) and flavored (honey) yoghurt samples. Yersinia pseudotuberculosis, Y. intermedia and Y. kristensenii could be isolated from the fruit yoghurt(strawberry) samples in percentages of 8%, 4% and 4%, respectively.
The sanitary and public health importance of isolated microorganisms as well as their control measures were discussed to improve the quality of fermented milk (yoghurt) to safe guard the consumers from infection.