الفهرس 
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Abstract
One hundred and fifty random samples of set yoghurt (75 produced at small scale and 75 produced at large scales) were collected from different and groceries supermarkets for sensory, chemical and microbiological examinations.
1- Sensory evaluation of yoghurt:
Quality scorecard for sensory evaluation which determined by comparing the properties or characteristics of each product with their accepted standard of perfection.
2- Keeping quality tests of yoghurt produced at small and large scale:
The mean values of titrable acidity for examined yoghurt samples were 1.12 ±0.023 for Yoghurt samples produced at small scale and 1.20 ±0.024 for yoghurt samples produced at large scale, respectively. The number of samples out of Egyptian Standard Specification was 2 (2.7%) for yoghurt samples produced at small scale and 1 (1.4 %) for yoghurt samples produced at large scale, respectively.
3- Microbiological evaluation of set yoghurt produced at small scale:
Coliform organisms, Staphylococcus aureus, Enterococci, Bacillus cereus, yeasts and total moulds were detected in 29 (38.7%), 70 (93.3 %), 34 (45.3%), 1(1.3%), 62 (82.7 %) and 63 (84%) of total yoghurt at small scale samples, respectively. Also, Salmonella species detected in 10 samples of yoghurt produced at small scale.
The mean values of total Coliform, Staphylococcus aureus, total Enterococci, Bacillus cereus, total yeast and mould counts for yoghurt at small scale samples were 3.67 x 103 ±1.41 x 103, 5.11 x 102 ± 6.1 x 10, 4.2 x 102 ±4.9 x 10, 1.8 x 102, 1.8 x 104 ±1.9 x 103, 4.6 x 103 ±6.5 x 102 , respectively. Salmonellae could by isolated from yoghurt produced at small scale at incidence of 10 (13.3 %).
The frequency distribution of isolated Coliform species from examined yoghurt samples produced at small scales were Enterobacter aerogenes 8(21%), Enterobacter Cloacae 5(13%), Enterobacter freundii 3(7.9%), Escherichia coli 10(26.4%), Klebsiella pneumoniae 3(7.9%), proteus mirabilis 4(10.6%), proteus vulgaris 2(5.3 %) and Serratia liquefaciens 3(7.9%).
The frequency distribution of isolated yeast species from yoghurt samples produced at small scale were Candida albicans 20 (27.5%), Candida krusei 15 (20.5%), Candida parapsillosis 5 (6.8 %), Candida pseudotropicalis 4 (5.6 %), Candida stellitaides 8 (10.9 %), Candida tropicalis 10 (13.7), Rhodotorula species 8 (10.9%), Saccharomyces species 1(1.4%) and Torulopis albus 2 (2.7 %), respectively.
The frequency distribution of isolated mould species from yoghurt samples produced at small scale were Alternaria Alternaria 22 (30.6%), Aspergillus flavus 12(16.7%), Aspergillus fumigatus 5 (6.9 %), Aspergillus niger 8 (11.1%), Cladosporium 7 (9.7%) , Fusarium 6 (8.3 %), Geotrichum candadum 1 (1.4%) , Mucor 2 (2.8%) ,Penicillium spp. 6 (8.3%) and Rhizopus spp. 3 (4.2%), respectively.
The number of yoghurt samples produced at small scale out of Egyptian standard Specification was 29 (38.7%), 70 (93.3%), 62 (82.7 %), 63 (84 %) and 10 (13.3 %) for Coliform organisms, Staphylococcus aureus, yeast, moulds and Salmonella, respectively.
3- Microbiological evaluation of yoghurt samples produced at large scale:
The mean values of total Coliform, Staphylococcus aureus, total Enterococci, Bacillus cereus, total yeast and total mould counts for yoghurt at large scale samples were 1.4 x 102 ±8.3 x 10, 3.6 x 102 ± 4.6 x 10, 4.4 x 103 1±.5 x 103, 1.8 x 103 ± 3.6 x102, 6.3 x 103 ±1. 6 x 103, 2.05 x 104 ±1.9 x 103, respectively. Salmonella could not be isolated from yoghurt samples produced at large scale.
Coliform organisms, Staphylococcus aureus, Enterococci, Bacillus cereus, yeasts and moulds counts were detected in 3 (4%), 41 (54.7 %), 4 (5.3%), 27 (36%), 26 (34.7 %) and 50 (66.7%) of total yoghurt samples at large scale, respectively. Also, Salmonella could not be detected in yoghurt samples produced at large scale.
The frequency distribution of isolated Coliform species from examined yoghurt samples produced at large scales were Enterobacter aerogenes 2(28.6%), Escherichia coli 3(42.8%), Klebsiella pneumoniae 1(14.3%) and proteus vulgaris 1(14.3 %).
The frequency distribution of isolated yeast species from yoghurt samples produced at large scale were Candida albicans 12 (30.7 %), Candida krusei 8 (20.5%), Candida parapsillosis 2 (5.2 %), Candida pseudotropicalis 3 (7.7 %), Candida stellitaides 2 (5. 2 %), Candida tropicalis 7 (18 %), Rhodotorula species 1 (2.5 %) and Saccharomyces species 4 (10.2%) respectively.
The frequency distribution of isolated mould species from yoghurt samples produced at large scale were Alternaria Alternaria 16 (25 %), Aspergillus flavus 10(15.6 %), Aspergillus fumigatus 2(3.1 %), Aspergillus niger 6 (9.4 %), Cladosporium 3 (4.7%) , Fusarium 8 (12.5 %), Geotrichum candadum 4 (6.2 %) , Mucor 5 (7.8%) ,Penicillium spp. 9 (14.1%) and Rhizopus spp. 1 (1. 6%), respectively.
The number of yoghurt samples produced at large scale out of Egyptian standard Specification were 3 (4 %), 41 (54.7%), 26 (34.7 %), 50 (66.7 %) and 0 (0 %) for Coliform organisms, Staphylococcus aureus, yeast, moulds and Salmonella, respectively
The significance and public health as well as economic importance of the isolated organisms were discussed and the suggestive control measures for improving the criteria and sanitary conditions of yoghurt were discussed
4- Addition of probiotic during manufacturing of yoghurt:
• When added lactobacillus acidophilus during manufacturing of yoghurt it was found that E.coli cannot be detected after 11 days, while when added bifidobacterium lactis E.coli cannot be detected after 10 days. When making mixture from two types of probiotics E.coli cannot be detected after 8 days.
• In case of Staphylococcus aureus, when added lactobacillus acidophilus or bifidobacterium lactis during manufacturing Staphylococcus aureus cannot be detected after 4 days, while when making mixture of both types of probiotics Staphylococcus aureus cannot be detected after 3 days.
• When added lactobacillus acidophilus as a probiotic during manufacturing of yoghurt Salmonellae cannot be detected after 4 days, while cannot be detected after 3 days in case of addition of bifidobacterium. In case of using both types (lactobacillus acidophilus and bifidobacterium lactis) Salmonellae cannot be detected after 3 days.
from the obtained results it was found that the addition of probiotic culture during manufacture of yoghurt give the greatest effect on suppression of pathogenic microorganisms under test with specially combination between two types of probiotic culture such as ( lactobacillus acidophilus and Bifidobacterium lactis).