الفهرس 
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Abstract
The low-fat cheese is healthy and eliminates the risk that resulted from full-fat cheese; especially if it is made with probiotics, which have many health benefits. The objectives of this study were to:
Using probiotic starters cultures in manufacturing low fat white soft cheese.
Studying the effect of probiotic starters cultures on chemical characteristics of low fat white soft cheese.
Studying the vitality of probiotics in low fat white soft cheese during the 30 days of the storage period.
Studying the effect of probiotic starters cultures on sensory properties of low fat white soft cheese.
Pasteurized buffalo’s and cow’s skim milk was divided into sixteen lots, and then 3% salt of sodium chloride was added into each. The first part of skim milk (control) coagulated by adding 4ml rennet/liter, while the other fifteen lots of skim milk were divided into 3 groups. Yogurt starter group (Y) contains T1, T2, and T3 tuned into cheese by using 4ml rennet/liter and yoghurt starter in three different proportions. Bifidobacteria starter group (B) which contain T4, T5, and T6 tuned into cheese by using 4ml rennet/liter and Bifidobacteria starter in three different proportions. The admixture group (Y+B) which contains T7, T8, T9, T10, T11, T12, T13, T14, and T15 tuned into cheese by using 4ml rennet/liter and mix of yoghurt and Bifidobacteria starters in nine different proportions. Cheeses from different treatments were sampled and analyzed when fresh (d=0), and after 7, 15, 21, and 30 days of storage period.
Chemical analysis:
Acidity percentage (%), moisture content, salt content, total protein (TP), soluble nitrogen (SN), and fat content were measured during the 30 days of storage.
Acidity:
There were a highly significant differences (p< 0.01) in the acidity of the low-fat probiotic soft white cheese between treatments and during the 30 days of storage period. The study showed that group Y, which was made using yoghurt starter, recorded higher acidity levels than group B, which were made with Bifidobacteria. Using a mixture of yoghurt starter, and Bifidobacteria led to raising the acidity.
Moisture:
There were highly significant differences (p< 0.01) in the moisture content of the low-fat probiotic soft white cheese between treatments and during the 30 days of storage period. The study showed that group (B) cheese samples maintained the highest moisture values during the storage period as compared with group (Y) and group (Y+B).
Total protein (TP):
There were highly significant differences (p< 0.01) in the total protein (TP) of the low-fat probiotic soft white cheese between treatments and during the 30 days of storage period. The study showed that group (Y) recorded higher TP as compared with other groups.
Soluble nitrogen (SN):
There were highly significant differences (p< 0.01) in the soluble nitrogen (SN) of the low-fat probiotic soft white cheese between treatments and during the 30 days of storage period. The study showed that group (Y+B) recorded higher SN as compared with other groups.
Fat and salt content:
There were highly significant differences (p< 0.01) in the fat and salt content of the low-fat probiotic soft white cheese between treatments and during the 30 days of storage period. The type or percentage of the starter had no direct effect on the fat content and salt content of cheese. The effect is mainly on the TS of the cheese.
Microbiological analysis:
Total bacterial count, Streptococci count, Lactobacillus count, Bifidobacterium count, yeasts, and molds count and coliform count was enumerated during the 30 days of storage.
Total bacterial count (TBC):
For all groups of cheeses, TBC increased during the first 15 days of the storage in all treatments except control. Subsequently, the TBC decreased until the end of storage. Control treatment increased during the first 21 days of the storage then the number decrease. The TBC of control was the highest compared to other treatments. group (Y) had higher TBC as compared to other groups. The TBC of the group (B) was the lowest compared to group (Y) and group (Y+B). On the other hand, mixing both groups (Y + B) did not markedly increase the TBC.
Lactobacilli count:
The study showed that control and group (B) treatments did not have any colonies during the storage period. group (Y), which contains yogurt starter culture, recorded the highest numbers of lactobacilli during 30 days of storage period. On the other hand, group (Y+B), which contains a mixture of yogurt starter culture with Bifidobacteria culture, recorded the lowest numbers of Lactobacilli during 30 days of storage as compared with group (Y). The total Lactobacilli count increased during the first 15 days of the storage period in group (Y) and group (Y+B) then the number decreased until the end of the storage period.
Streptococci count:
The study showed that no colonies were found either in control or group (B) treatments. group (Y), which contains yogurt starter culture, recorded the highest numbers of Streptococci during 30 days of storage period as compared with group (Y+B). In group (Y) and group (Y+B), total Streptococci count increased until the 15th of storage period then the number decreased until the end of the storage period.
Bifidobacterium count:
The study showed that control and group (Y), have no colonies have grown. For all treatment of group (B) and group (normal decrease. Admixing Bifidobacteria with Yoghurt starter in group (Y+B) did not affect the total Bifidobacteria count.
Generally, in all treatments in both group (B) and group (Y+B) After 30 days the highest Bifidobacteria colonies were 6.76 log CFU/g and 6.83 log CFU/g for T4 and T5 respectively. These numbers are ranged between 105 -107 which accomplish the requested bioactive numbers.
Yeasts and molds count:
The molds and yeast counts in all treatments were detected in lower numbers after 15 days of the storage period, then the number started to increase by extending the storage period as a result of acidity development.
Coliform count:
The results were negative in all these tests for all treatments during the storage period (30 days). This is due to the pasteurization of milk before the manufacturing of cheese, which eliminates pathogenic bacteria.
Sensory evaluation:
Sensory evaluation was done by a regular taste panel of the staff members of the Dairy Science Department, Faculty of Agriculture, Assiut University. Samples were evaluated for flavor (50 points), color and appearance (15 points), and body and texture (35 points) to be 100 points for the total score.
Color and appearance:
The color and appearance of all cheeses did not markedly affect by adding starters since the cheese was kept at refrigerator conditions. A few colonies of fungi or surface microorganisms have appeared after 21 days of the storage period in some samples.
Body and texture:
The starter had a slight effect on the body and texture of the cheese which gained higher scoring points during the ripening time. The admixture starters group (Y+B) gained the highest Body and Texture of the cheese compared with other groups. The textural and body of group (B) was to some extent softer than group (Y) and group (Y+B).
Flavor:
The flavor of all cheeses increased since the cheese was kept at refrigerator conditions. The admixture starter cheeses group (Y+B) gained higher flavor and aroma scoring points. On the other hand group (B) had Bifidobacteria gained the lowest flavor and aroma scoring points. group (Y) gained stronger flavor as compared with group (B). Generally, the admixture culture cheese group (Y+B) was more acceptable having scoring points followed by yoghurt culture cheese group (Y) and lastly Bifidobacteria starter cheese group (B) treatments.
Generally, it is possible to produce good low fat white soft cheese having a higher sensory evaluation from mixed of cow and buffalo milk using admixture starter containing probiotic bacteria. Possibly to offer low fat white soft cheese with excellent flavor in a shorter time one month having alive probiotic bacteria that support the activity of human health.
It is recommended to use the admixture starters for the manufacturing of low-fat white soft cheese to gain the accepted flavored cheese and the high health benefits of probiotics bacteria because Egyptian people are consuming high amounts of soft cheese compared to hard cheese and fermented milk products consumers.
from the foregoing results, it could be concluded that:
Low-fat cheese can be produced from pasteurized skim milk with a good flavor and texture using probiotic bacteria starters.
Low-fat cheese can be stored for 30 days with enough probiotic bacteria (5-7) log cfu/g.
High-quality Low-fat cheese produced from using a mix of yogurt starter cultures (group Y) and Bifidobacteria (group B) at a ratio of 0.5%+0.5% respectively. However, using Bifidobacterium (group B) only in making low-fat cheese resulted in poor flavor cheese with a soft texture.