الفهرس 
Acknowledgements
Chemical composition of Laban RayebOnly 14 pages are availabe for public view
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Abstract
This work was carried out to evaluate the chemical composition and microbiological quality of Laban Rayeb produced by small dairy plant in Assuit city, as well as to isolate lactic acid groups, and used it to produce Laban Rayeb under a good sanitation and hygiene conditions. Investigated samples were collected from 12 small dairy plants in Assiut city.
A. Collected Laban Rayeb:
1. Chemical composition of collected Laban Rayeb:
1.1. Titratable acidity:
The mean values of titratable acidity in the examined collected Laban Rayeb samples are ranged from 0.76 to 1.33% with a general average of 1.01%.
1.2. Total solids content:
The percentages of total solids in the examined collected Laban Rayeb samples are ranged from 9.53 to 13.3% with a general average 11.66%.
1.3. Moisture content:
The percentages of moisture content in the examined collected Laban Rayeb samples are ranged from 86.70 to 90.47% with a general average 88.29%.
1.4. Total nitrogen content:
The percentages of total nitrogen content in the examined collected Laban Rayeb samples are ranged from 0.45 to 0.61% with a general average 0.52%.
1.5. Soluble nitrogen content:
The percentages of soluble nitrogen in the examined collected Laban Rayeb samples are ranged from 0.110 to 0.207% with a general average 0.170%.
1.6. Soluble nitrogen coefficient:
The mean values of soluble nitrogen coefficient in the examined collected Laban Rayeb samples are ranged from 24.4 to 41.7 with a general average 32.7.
1.7. Fat content:
The fat percentages in the examined collected Laban Rayeb samples are ranged from 0.33 to 4.10% with a general average 2.41%.
2. Microbiological properties of collected Laban Rayeb:
2.1. Total bacterial count (T.B.C.):
The final results of total bacterial counts showed that, the range was 7.03-7.21 log cfu/ml in the examined collected Laban Rayeb samples.
2.2. Lactic acid bacterial count (L.A.B.):
The microbiological analysis of the investigated samples showed that, the counts of both Lactobacillus spp. and Streptococcus spp. were range from 5.78 to 6.35 and from 5.83 to 6.29 log cfu/ml, respectively.
2.3. Molds and yeasts count:
The results showed that, all the collected samples from small plants in Assiut city evolve of molds and yeasts except for the sample which obtained from Dairy Products Unit. Moulds and yeasts counts were range from 3.08 to 5.21 log cfu/ml.
2.4. The proteolytic bacterial count:
The obtained results of proteolytic bacteria counts are ranged from 4.36 to 6.89 log cfu/ml.
2.5. The incidence of coliform bacteria:
Coliform bacteria in investigated Laban Rayeb samples were not detected in all collected samples.
B. Manufacturing Laban Rayeb:
In this part, Lactobacillus spp. colonies were isolated using MRS medium and Streptococcus spp. using M17 medium in a pure culture. Cow’s milk heated to 73°C for 15 seconds and cooled to 37°C, and then inoculated by a single isolated culture or mixture of them at 1 : 1 by weight, to produce a Laban Rayeb in sterile laboratory conditions. The produced Laban Rayeb was stored for 15 days at 5 ± 2°C.
1. Chemical composition of manufacture of Laban Rayeb:
1.1. Titratable acidity:
The mean acidity values in control Laban Rayeb was ranged from 0.70% on the first day of storage and increased to 0.86% after 15 days of storage. While the mean acidity in the samples of Laban Rayeb produced by Streptococcus spp. ranged from 0.74% on the first day of storage and increased with storage to 0.95% after 15 days. While the acidity values of Laban Rayeb inoculated by Lactobacillus spp. was 0.76%, at first day of storage, and increased to 0.96% after 15 days of storage. The Laban Rayeb produced using Lactobacillus spp. and Streptococcus spp. gave an acidity of 0.84% at first day of storage, and by increasing the storage periods, the acidity values was increased to 1.20% after 15 days of storage.
1.2. Total solids content:
The total solids percentages of Laban Rayeb produced increased from 11.36% at fresh to reach 11.52% after 15 days of storage for control samples. While the mean values of Laban Rayeb produced at laboratory conditions using; Streptococcus spp., Lactobacillus spp. and mixture of them (1:1) were 11.33% at fresh to 12.22 after 15 days, 11.16% at fresh to 11.75% after 15 days and 11.60 at fresh to 11.90% after 15 days of storage, respectively.
1.3. Moisture content:
The moisture contents of Laban Rayeb produced, decreased from 88.63% at fresh to reach 88.48% after 15 days of storage for control samples. While the moisture mean values of Laban Rayeb produced at laboratory conditions using Streptococcus spp., Lactobacillus spp. and mixture of them (1:1) were 88.67% at fresh to 87.77% after 15 days, 88.83% at fresh to 88.24% after 15 days and 88.39% at fresh to 88.10% after 15 days of storage, respectively.
1.4. Total nitrogen content:
The mean total nitrogen values in control Laban Rayeb was ranged from 0.44% on the first day of storage and increased to 0.49% after 15 days of storage. While the mean total nitrogen in the samples of Laban Rayeb produced by Streptococcus spp. was ranged from 0.44% on the first day of storage and increased with storage to 0.52% after 15 days. While the total nitrogen values of Laban Rayeb inoculated by Lactobacillus spp. was 0.45%, at first day of storage, and increased to 0.52% after 15 days of storage. The Laban Rayeb produced using mixture (Lactobacillus spp. and Streptococcus spp.) gave total nitrogen of 0.42% and by increasing the storage period, total nitrogen content values was increased to reach 0.51% after 15 days of storage.
1.5. Total protein content:
The total protein percentages of Laban Rayeb produced, increased from 2.8% at fresh to reach 3.1% after 15 days of storage for control samples. While the mean values of Laban Rayeb produced at laboratory conditions using Streptococcus spp., Lactobacillus spp. and mixture of them (1:1) were 2.8% at fresh to 3.3% at 15 days, 2.9% at fresh to 3.3% after 15 days and 2.7% at fresh to 3.3% after 15 days of storage, respectively.
1.6. Soluble nitrogen content:
The mean soluble nitrogen values in control Laban Rayeb was ranged from 0.112% on the first day of storage and increased to 0.169% after 15 days of storage. While, the mean soluble nitrogen in the samples of Laban Rayeb produced by Streptococcus spp. was ranged from 0.114% on the first day of storage and increased with storage to 0.160% after 15 days. Also, the soluble nitrogen value of Laban Rayeb inoculated by Lactobacillus spp. was 0.103%, at first day of storage, and increased to 0.164% after 15 days of storage. The Laban Rayeb produced using Lactobacillus spp. and Streptococcus spp. gave soluble nitrogen of 0.123% and by increasing the storage period, soluble nitrogen content values was increased to 0.192% after 15 days of storage.
1.7. Fat content:
The mean value of fat in the control of Laban Rayeb, produced using Streptococcus spp., Lactobacillus spp. and mixture of Lactobacillus spp. & Streptococcus spp. gave, on the first day of storage, 3.6% and with storage after 15 days 3.6%.
2. Microbiological quality of manufacturing Laban Rayeb:
2.1. Total bacterial count:
The mean logarithm of total bacterial count in control Laban Rayeb was ranged from 5.12 log cfu/ml on the first day of storage and increased to 8.87 log cfu/ml after 15 days of storage. While, the mean logarithm of total bacterial count of Laban Rayeb produced by Streptococcus spp. was ranged from 6.21 log cfu/ml on the first day of storage and increased with storage to 9.13 log cfu/ml after 15 days. Moreover, the mean logarithm of total bacterial count of Laban Rayeb inoculated by Lactobacillus spp. was 6.27 log cfu/ml at first day of storage, and increased to 9.20 log cfu/ml after 15 days of storage. The Laban Rayeb produced using Lactobacillus spp. and Streptococcus spp. gave mean logarithm of total bacterial count of 6.29 log cfu/ml, and by increasing the storage period, the mean logarithm of total bacterial values was increased to 8.64 log cfu/ml after 15 days.
2.2. Lactobacillus spp. count:
The mean logarithm of lactic acid bacteria of Lactobacillus spp. count in control Laban Rayeb was ranged from 5.21 log cfu/ml on the first day of storage, and increased to 7.73 log cfu/ml after 15 days of storage. While, the mean logarithm of lactic acid bacteria of Lactobacillus spp. count of Laban Rayeb produced by Streptococcus spp. was ranged from 5.46 log cfu/ml on the first day of storage and increased with storage to 8.13 log cfu/ml after 15 days. Moreover, the mean logarithm of lactic acid bacteria of Lactobacillus spp. count of Laban Rayeb inoculated by Lactobacillus spp. was 7.14 log cfu/ml at first day of storage, and increased to 9.22 log cfu/ml after 15 days of storage. The Laban Rayeb produced using Lactobacillus spp. and Streptococcus spp. gave mean logarithm of lactic acid bacteria of Lactobacillus spp. count of 7.15 log cfu/ml, and by increasing the storage period mean logarithm of Lactobacillus spp. values was increased to 9.46 log cfu/ml after 15 days.
2.3. Streptococcus spp. count:
The mean logarithm of lactic acid bacteria of Streptococcus spp. count in control Laban Rayeb was ranged from 4.86 log cfu/ml on the first day of storage and increased to 7.42 log cfu/ml after 15 days of storage. While, the mean logarithm of lactic acid bacteria of Streptococcus spp. count of Laban Rayeb produced by Streptococcus spp. was ranged from 6.93 log cfu/ml on the first day of storage, and increased with storage to 9.89 log cfu/ml after 15 days. Moreover, the mean logarithm of lactic acid bacteria of Streptococcus spp. count of Laban Rayeb inoculated by Lactobacillus spp. was 4.12 log cfu/ml at first day of storage, and increased to 8.17 log cfu/ml after 15 days of storage. The Laban Rayeb produced using Lactobacillus spp. and Streptococcus spp. gave mean logarithm of lactic acid bacteria of Streptococcus spp. count of 6.81 log cfu/ml, and by increasing the storage period, mean logarithm of lactic acid bacteria of Streptococcus spp. count was increased to reach 8.76 log cfu/ml after 15 days.
2.4. Proteolytic bacterial count:
The mean logarithm proteolytic bacterial count in control Laban Rayeb was ranged from 1.61 log cfu/ml on the first day of storage and increased to 5.34 log cfu/ml after 15 days of storage. While, the mean logarithm of proteolytic bacterial count of Laban Rayeb produced by Streptococcus spp. was ranged from 3.54 log cfu/ml on the first day of storage, and increased with storage to 6.45 log cfu/ml after 15 days. Moreover, the mean logarithm of proteolytic bacterial count of Laban Rayeb inoculated by Lactobacillus spp. was 3.18 log cfu/ml at first day of storage, and increased to 6.56 log cfu/ml after 15 days of storage. The Laban Rayeb produced using Lactobacillus spp. and Streptococcus spp. gave mean logarithm of proteolytic bacterial count of 3.32 log cfu/ml, and by increasing the storage period, means logarithm of proteolytic bacterial values was increased to 6.75 log cfu/ml after 15 days.
2.5. Moulds and yeasts count:
The results showed that, moulds and yeasts count in investigated manufacture Laban Rayeb samples were not detected.
2.6. The incidence of coliform bacteria:
Coliform bacteria in investigated manufacture Laban Rayeb samples were not detected.
C. Comparison between collected and fresh manufactured Laban Rayeb:
1. Chemical comparison:
1.1 Titratable acidity:
The comparison of titratable acidity percentages of the examined Laban Rayeb samples obtained from small dairy factories and manufacture samples are given the value of; 1.01, 0.70, 0.74, 0.81 and 0.83% in collected samples, control, cocci shape, rod shape and mixture of both; respectively. Control samples showed the lowest titratable acidity, while that of collected Laban Rayeb showed the highest titratable acidity.
1.2. Total solids content:
The comparison of total solid content of the examined Laban Rayeb samples obtained from small dairy factories and manufacture samples are given the value of; 11.66, 11.36, 11.33, 11.16 and 11.60% in collected samples, control, cocci shape, rod shape and mixture of both; respectively. Rod shape samples showed the lowest titratable acidity, while that of collected showed the highest total solid content.
1.3. Moisture content:
The comparison of moisture percentages of the examined Laban Rayeb samples obtained from small dairy factories and manufacture samples are given the value of; 88.29, 88.63, 88.67, 88.83 and 88.39% in collected samples, control, cocci shape, rod shape and mixture of both, respectively. Collected samples showed the lowest moisture content, while that of rod shape samples showed the highest moisture content.
1.4. Total nitrogen content:
The comparison of total nitrogen percentages of the examined Laban Rayeb samples obtained from small dairy factories and manufacture samples are given the value of; 0.52, 0.44, 0.44, 0.45 and 0.42% in collected samples, control, cocci shape, rod shape and mixture of both, respectively. Mixture samples showed the lowest total nitrogen content, while that of collected samples showed the highest total nitrogen content.
1.5. Total protein content:
The comparison of total protein percentages of the examined Laban Rayeb samples obtained from small dairy factories and manufacture samples are given the value of; 3.4, 2.8, 2.8, 2.9 and 2.7% in collected samples, control, cocci shape, rod shape and mixture of both; respectively. Mixture samples showed the lowest total protein content, while that of collected samples showed the highest total protein content.
1.6. Soluble nitrogen content:
The comparison of soluble nitrogen percentages of the examined Laban Rayeb samples obtained from small dairy factories and manufacture samples are given the value of; 0.170, 0.112, 0.114, 103 and 0.123% in collected samples, control, cocci shape, rod shape and mixture of both; respectively. Rod shape samples showed the lowest soluble nitrogen content, while that of collected samples showed the highest soluble nitrogen content.
1.7. Fat content:
The comparison of fat percentages of the examined Laban Rayeb samples obtained from small dairy factories and manufacture samples are given the value of; 2.4 and 3.6% in collected and manufacture samples (control, cocci shape, rod shape and mixture), respectively. Collected samples showed the lowest fat content, while that of manufacture samples showed the highest fat content.
2. Microbiological comparison:
2.1. Total bacterial count:
The comparison of total bacterial count of the examined Laban Rayeb samples obtained from small dairy factories and manufacture samples are given the value of; 7.13, 5.12, 6.21, 6.27 and 6.29 log cfu/ml in collected samples, control, cocci shape, rod shape and mixture of both; respectively. Control samples showed the lowest total bacteria count, while that of collected samples showed the highest total bacterial count.
2.2. Streptococcus spp. count:
The comparison of Streptococcus spp. count of the examined Laban Rayeb samples obtained from small dairy factories and manufacture samples are given the value of; 6.07, 4.86, 6.93, 4.12 and 6.81 log cfu/ml in collected samples, control, cocci shape, rod shape and mixture of both; respectively. Rod shape samples showed the lowest Streptococcus spp. count, while that of cocci shape samples showed the highest Streptococcus spp. count.
2.3. Lactobacillus spp. count:
The comparison of Lactobacillus spp. count of the examined Laban Rayeb samples obtained from small dairy factories and manufacture samples are given the value of; 6.10, 5.21, 5.46, 7.14 and 7.15 log cfu/ml in collected samples, control, cocci shape, rod shape and mixture of both; respectively. Control samples showed the lowest Lactobacillus spp. count, while that of mixture samples showed the highest Lactobacillus spp. count.
2.4. Proteolytic bacterial count:
The comparison of proteolytic bacterial count of the examined Laban Rayeb samples obtained from small dairy factories and manufacture samples are given the value of; 5.60, 1.61, 3.54, 3.18 and 3.32 log cfu/ml in collected samples, control, cocci shape, rod shape and mixture of both; respectively. Control samples showed the lowest proteolytic bacterial count, while that of collected samples showed the highest proteolytic bacterial count.
2. 5. Moulds and yeasts count:
The comparison of moulds and yeasts count of the examined Laban Rayeb samples obtained from small dairy factories and manufacture samples are given the value of, 4.34 log cfu/ml in collected samples; whilst, they had not been detected in manufacture samples.
2. 6. Coliform bacterial incidence:
Concerning to the incidence of coliform bacteria, the obtained data from microbiological analyses of the samples showed that, the coliform bacterial count had not been detected in all investigated samples.