الفهرس 
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Abstract
Probiotics are “live microorganisms which when administered inadequate numbers confer a health benefit on the host”. These bacteria beneficially affect human health by improving the balance of intestinal microflora and improving mucosal defenses against pathogens. Prebiotics is defined as “a non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon”; a synbiotic is a combination of prebiotics and prebiotics that “beneficially affects the host by improving the survival and the implantation of live microbial dietary supplements in the gastro intestinal tract by selectively stimulating the growth and/or by activating the metabolism of one or a limited number of health promoting bacteria”. Cheese is a dairy product which has a good potential for delivery of probiotic microorganisms into the human intestine due to, its specific chemical and physical characteristics compared to fermented milks.
Consequently, the obtained results can be summarized as follow:
1) Effect of growth promoting substances on
promoting substances, i.e.; yeast extract, fructose and peptone on the growth rate of Bif. bifidum in sterilized skim milk:
Effects of different percentages of some growth the growth rate and acid production by Bif. bifidum in sterilized skim milk at
40˚C was studied. Growth promoting substances were added to milk
in three different concentrations, i.e.; 0.1, 0.3, and 0.5%.
The three substances resulted in an increased of growth and acid production by Bif. bifidum.
The maximum plate counts in the presence of yeast extract were
25x104, 12x105 and 21x105 CFU/ml; in the presence of 0.1, 0.3 and
0.5% after 12 hours of incubation at 40˚C; respectively. Similar effect was found in the presence of fructose and peptone, where the maximum cell population after 12 hours of incubation reached to
35x104, 46x104 & 53x104 and 25x104, 51x104 & 40x105 CFU/ml;
respectively.
There were direct relationship between the rate of increase in CFU
and DTA (developed titratable acidity).
The highest count of Bif. bifidum was obtained in milk supplied with good source nitrogenous compounds such as peptone which can be explained by the effect of availability nitrogenous compounds in milk which can enhance the rate of growth and increase in CFU of Bif. bifidum.
2) Probiotic fermented milk:
In this study some probiotic fermented milks were studied, and all these treatments were tested for chemical, microbiological and sensory properties i.e.; Acidity, Total bacterial count, Bif. bifidum count and sensory evaluation:
A) Commercial probiotic yoghurt available in the local markets
(Activia probiotic yoghurt):
The obtained results indicated that, in commercial probiotic yoghurt (Activia) and during 2 weeks of storage at 5-7˚C, the developed titratable acidity was affected by the storage period, and it was increased by a steady rate and reached to the higher value at the end of the storage period (1%).
Total bacterial count was gradually decreased and reached to the minimum counts at the end of storage period (30x105 CFU/ml).
Colony counts of Bif. bifidum was slowly decreased up to the end of storage and reached 69x105 CFU/ml.
B) Probiotic fermented milk manufactured in the laboratory:
T1: Probiotic yoghurt inoculated with active starter culture of 10% Str. thermophilus and 10% Lb. delbruckii subsp bulgaricus.
T2: Probiotic yoghurt inoculated with active starter culture of 10% (Str. thermophilus and Lb. delbruckii subsp bulgaricus, 1: 1) and 15% Bif. bifidum.
T3: Probiotic Acidophilus milk inoculated with active starter culture of
1% Lb. acidophilus and 15% Bif. bifidum.
T4: Probiotic yoghurt inoculated with 20% of Activia yoghurt.
T5: Probiotic Acidophilus milk inoculated with active starter culture of
10% Lb. acidophilus.
T6: Probiotic Acidophilus milk inoculated with active starter culture of
6% Lb. acidophilus and 15% Bif. bifidum.
Treatment 1 (T1):
- Total bacteria count was increased and reached to its maximum counts at the end of storage period, being 46x105 CFU/ml.
- The developed titratable acidity was affected by the storage period, and it was increased slightly and reached to the higher value at the end of the storage period (0.90%).
Treatment 2 (T2):
- The titratable acidity was affected by the storage period, and it was increased slightly and reached to the higher value at the end of the storage period being (0.90%).
- Total bacterial count decreased and reached to the minimum counts at the end of storage period 13x105 CFU/ ml.
- Counts of Bif. bifidum declined slowly up to the end of storage and reached to 28x104 CFU/ml.
Treatment 3 (T3):
- The obtained results indicated that, DTA was increased by a slow rate, being 0.30% at fresh and it was reached to 0.41% at the end of storage period.
- Total bacterial count of CFU was slightly affected by the storage, and it was decreased from 31x106 CFU/ml at fresh and reached to 22x106
CFU/ml at the end of the storage period.
- Similar results were obtained with colony count of Bif. bifidum, where it was 35x106 CFU/ml at fresh, and it was decreased reaching to
14x106 CFU/ml at the end of the storage period.
Treatment 4 (T4):
- DTA was slightly increased during storage and it was increased from o.57% at fresh and it reached to o.84% at the end of storage.
- In probiotic fermented milk (Activia), the total bacterial count was slowly decreased during storage, and it was 47x106 CFU/ml at fresh, and it was decreased to 30x105 CFU/ml at the end of storage.
- Colony forming units of Bif. bifidum was decreased by a slow rate and it was 60x106 CFU/ml at fresh and reached to 68x104 CFU/ ml at the end of storage (11 days).
Treatment 5 (T5):
- Total bacterial count of CFU was gradually increased during the first
9 days of incubation, and it was raised from 50x105 CFU/ml at the first day and reached to 31x106 CFU/ml after 9 days of storage, and then decreased to 30x106 CFU/ml after 11 days of storage, this can be explained by the gradual increase in DTA which it was raised from
0.41% at the first day and it was reached 0.52% after 11 days of storage.
Treatment 6 (T6):
- Total bacterial count of CFU was gradually increased during the first
9 day of storage, and it was increased from 10x106 CFU/ml at fresh and reached to 38x106 CFU/ml after 9 days of storage, and then decreased to 37x106 CFU/ml after 11 days. The corresponding values for Bif. bifidum were 26x104 CFU/ml, and it was gradually and slowly increased and reached to 12x106 after 9 days of storage, and then decreased to 11x106 CFU/ml after 11 days of storage. This can be explained by the increase in the DTA which can affect the
bacterial growth.
C) Sensory properties of probiotic fermented milk:
- Concerning the organoleptic properties of probiotic fermented milk, the results indicated that, degree of acceptability of manufacture yoghurt (T1, T2 and T4) were slowly decreased from the first day of storage up to the 10th day.
- Concerning the organoleptic properties of fermented milk drink (T3, T5 and T6); there were an increase in the degree of acceptability as the storage prolonged in all treatments.
- Appearance of fermented milk drink was decreased as the storage period increased this may be explained by the aggregation of fat globules on the surface layer as milk was not homogenized.
3) Probiotic soft cheese:
Total CFU was gradually decreased in all cheese samples during storage, and it was affected by the percentage of salt. In cheese samples manufactured by using 3% salt, the total CFU was 32x107
CFU/ml at fresh, and it was decreased to 13x105 CFU/ml after 60
days of storage. The corresponding values for cheese samples manufactured by 5 and 7% sodium chloride were 22x107 & 10x105 and 53x106 & 30x104 CFU/ml; respectively.
Increasing the percentage of added salt to milk decreased number of CFU of Bif. bifidum in the resultant cheese either in fresh cheese or at the end of the storage period of 60 days. In cheese contained 3% sodium chloride, count of CFU of Bif. bifidum was 32x106 and
54x104 CFU/ml at fresh and after the storage period; respectively.
The corresponding values for cheese manufacture by 5 and 7% sodium chloride, the corresponding values were 73x105 & 32x104 and 54x105 & 10x103 CFU/ml; respectively.
The results can be explained by the effect of sodium chloride which decreases the bacterial growth and acid production.
The highest values of DTA over all the storage period were in cheese samples manufactured by using 3% NaCl comparing with cheese samples manufactured by using 5 or 7% NaCl.
The moisture content in all cheese samples was gradually decreased during storage and was slightly affected by the percentage of added salt.
Coliform bacteria were not detected in all samples over the storage period of 60 days.
Addition of salt remarkably enhanced the sensory quality attributes of flavor, body & texture, appearance and consequently the total acceptability (overall score) of resultant product. This may be attributed to the higher acidity development in treated cheese, which could enhance the texture of resultant cheese. Body & texture as well as flavor and consequently cheese acceptability improved during pickling of cheese.
The flavor enhancement in probiotic soft cheese is due to the role of starter to hydrolyze the milk component involved in cheese flavor such as; proteins, fats, lactose, citrates and phosphates. There were big differences in flavor score of fresh high salted cheese treatment (7%) and low salt cheese treatment (3%). This is due to salty taste that covers the cheese aroma.
The overall score of probiotic cheese increased during period of pickling.
At the end of pickling, cheese of T3 was the best, while, T1 cheese was the lowest among all samples.