الفهرس 
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Abstract
Labneh is one of the most famous dairy products in different parts of the world, especially in the Middle East. where it plays an important role in food systems. Its outstanding food benefits and conservation characteristics have increased its economic importance. Therefore, the aim of this study was to develop and evaluate the quality of a functional Labneh using probiotic bacteria and using various functional fats.
Probiotics are defined as living microorganisms, which, when ingested in sufficient amounts, beneficially influence the health of the host by improving the composition of intestinal microflora. In addition to improving gut health, probiotics may play a beneficial role in several medical conditions, including lactose intolerance, cancer, allergies, hepatic disease, Helicobacter pylori infections, urinary tract infections, hyperlipidemia and assimilation of cholesterol. Probiotic microorganisms that are known to be beneficial to human health can be ingested through fermented dairy products, enrichment of various foods with these bacteria and consumption of pharmaceutical products that are obtained by using viable cells (lyophilized preparations and tablets).
Volatile oils, also known as essential oils are lipophilic compounds containing volatile aroma compounds. They are generally isolated from non-woody plant materials by distillation methods, solvent extraction or cold expression. They are used in perfumes, cosmetics, flavouring food and drinks and for scenting. Medicinal uses proposed by sellers of essential oils vary from skin treatments to remedies for cancer.
Citrus is grown widely all over the world for its numerous health benefits. Citrus fruits are consumed as a fresh fruit dessert or used for making juice and jam. They are an excellent source of vitamins, especially vitamin C. Processing Citrus fruits results in a significant amount of waste (peels, seeds, and pulps), which accounts for 50% of the fruit. Citrus waste is a valuable source of d-limonene, flavonoids, carotenoids, dietary fibers, soluble sugars, cellulose, hemicellulose, pectin, polyphenols, ascorbic acid, methane, and essential oils. Interestingly, the essential oil (EO) is the most vital by-product of Citrus processing. Citrus EOs are broadly used as natural food additives in several food and beverage products because they have been classified as generally recognized as safe. Furthermore, Citrus EOs are used as natural preservatives due to their broad spectrum of biological activities including antimicrobial and antioxidant effects. The presence of terpenes, flavonoids, carotenes, and coumarins is thought to be responsible for the strong anti-oxidative and antimicrobial activities. Due to their pleasant, refreshing smell and rich aroma, Citrus EOs are also used in air-fresheners, household cleaning products, perfumes, cosmetics and medicines.
This study has been carried out in two parts:
Part Ι: Effect of starter culture on the quality of labneh:
It has been concerned with this part to investigate the effect of some probiotic bacteria on some chemical, rheological and organoleptic properties of Labneh therefore 5 treatments of Labneh were made. Control Labneh treatment was prepared without probiotic bacteria. The other four treatments were made by adding (1%) Lb. acidophilus, Bif. bfidum, Lb. plantarum, while the fourth treatment was made by a mixture of the previous three bacteria (1 : 1 : 1%) (T1, T2, T3 and T4), respectively.
All treatments were stored in the refrigerator for 21 days and were sampled at 0, 7, 14 and 21 days of storage period to evaluate the organoleptic, chemical, microbiological and rheological properties.
The obtained results can be summarized as follow:
1- The type of starter culture added during the manufacture affected significantly the titratable acidity and pH values of the resulted Labneh. Treatment (T4) that made with a mixture of probiotic bacteria had the highest titratable acidity, while control labneh treatment had the lowest titratable acidity. Acidity of all Labneh treatments increased as a storage period advanced.
2- pH values of all Labneh treatments followed an opposite trend to those of titratable acidity.
3- Type of starter culture added during the manufacture of Labneh treatments affected significantly the total solids, protein, fat, lactose, acetaldehyde, and diacetyl content. Treatment (T4) that was made by adding a mixture of probiotic bacteria contained the highest total solids, total protein, fat contents, followed by treatments T1 and T3, which were made by adding L. acidophilus and L. plantarum respectively and then T2 and C Labneh treatments. Total solids, total protein and fat content increased slightly during the storage period.
4- Labneh treatments were significantly different from each other in lactose and ash content. Control Labneh treatment that made without adding probiotic bacteria contained the highest lactose and ash content, while T4 and T1 those made by adding a mixture of probiotic bacteria and L. acidophilus, respectively contained the lowest ash and lactose contents. Ash content of all Labneh treatments increased slightly, while lactose content decreased throughout the storage period.
5- Acetaldehyde and diacetyl contents increased with addition of probiotic bacteria. Treatments T4 and T3 those made by adding a mixture of probiotic bacteria and L. plantarum contained the highest values of acetaldehyde and diacetyl. Acetaldehyde and diacetyl contents of all Labneh treatments increased during the first seven days of storage period, then decreased gradually up to the end of storage period.
6- Texture profile of Labneh treatments were significantly different from each other which means that probiotic bacteria had a significant effect on the texture profile of Labneh treatments. Treatment (T4) that made by adding a mixture of probiotic bacteria exhibited the highest treatment values of hardness, adhesiveness, cohesiveness, springiness, chewiness and viscosity followed by treatments T1 and T3 those made with adding L. acidphilus and L. plantarum, respectively then T2 and C. Hardness, cohesiveness, Gumminess, chewiness and viscosity of all Labneh treatments increased during the storage period, while adhesiveness and springiness decreased.
7- Scores of flavor, body and texture, Appearance and total scores of the organoleptic properties of all Labneh treatments followed similar trends. Labneh treatments were accepted by the panelists, but the most acceptable treatment was T3 that made by adding1% of Lb. plantarum.
8- Total bacterial, L. acidphilus, Bif. bifidum and L. plantarum counts followed similar trends during cold storage of Labneh, Their counts increased during the first seven days of storage and reached their maximum counts on the seventh day of storage, then their counts decreased gradually as storage period proceeded. The counts of each probiotic bacteria, even after 21 days of storage were higher than the mumbers should be present in food products to achieve their health benefits, therefore probiotic Labneh could be a good vehicle for delivering the probiotic bacteria to the consumers.
Part II: Quality of probiotic labneh supplemented with mandarin oil:
It has been concerned with this part to investigate the effect of adding mandarin oil on the chemical, rheological, microbiological and organoleptic properties of probiotic Labneh. Therefore 5 treatments of Labneh were made. Control Labneh treatment was made without adding mandarin oil. The other four treatments were made by adding 0.1, 0.2 0.4, 0.6% mandarin oil, respectively.
All treatments were stored in the refrigerator for 21 days and were sampled at 0, 7, 14 and 21 days of storage period to evaluate the organoleptic, chemical, microbiological and rheological properties of Labneh treatments.
The obtained results can be summarized as follow:
1- Addition of mandarin oil to Labneh caused a significant reduction of titratable acidity and this reduction was proportional to the rate of adding mandarin oil. Titratable acidity of all Labneh treatments increased during storage period.
2- pH values of Labneh treatments as affected by mandarin oil and storage period followed an opposite trend to those of acidity.
3- Adding mandarin oil increased slightly the total solids, fat and lactose contents of Labneh treatments and this increase was proportional to the rate of adding mandarin oil. Total solids and fat contents increased, while the lactose content of all Labneh treatments decreased as storage period proceeded.
4- Labneh treatments were not significantly different from each other in protein and ash content which means that mandarin oil did not have a significant effect on the protein and ash contents. Protein and ash contents of all Labneh treatments increased slightly as the storage period progressed.
5- Adding mandarin oil caused a significant reduction of acetaldehyde and diacetayl content. Control Labneh and T1 those made by adding 0.0 and 0.1% mandarin oil were not significantly different from each other and contained the highest concentration of acetaldehyde and diacetyl. On the other hand, acetaldehyde and diacetyl contents of all Labneh treatments increased up to the seventh day of storage, period then decreased up to the end of storage period.
6- Texture profile of Labneh treatments were significantly different from each other which means that mandarin oil did have a significant effect on the texture profile of Labneh.
7- Scores of flavor, body and texture, Appearance and total scores of the organoleptic properties of all Labneh treatments followed similar trends. Labneh treatments were accepted by the panelists, but the most acceptable treatment was T1 that made by adding 0.1% of mandarin oil.
8- Total bacterial counts of all treatment followed similar trends during cold storage of Labneh, Their counts increased during the first seven days of storage and reached their maximum counts on the seventh day of storage, then their counts decreased gradually as storage period proceeded. On the other hand, adding of mandarin oil caused a significant decrease of the counts of total bacteria and the counts of L. plantarum.
Conclusion:
It could be concluded that incorporation of probiotic bacteria during the manufacture of Labneh increased the titratable acidity, total solids, protein, fat, acetaldehyde and diacetyl contents of the resulting Labneh treatments, while decreasing the ash and lactose contents. It also increased all the values of texture parameters (hardness, Adhesiveness, Cohesiveness, Springiness, Gumminess, and Chewiness, viscosity and improved the acceptability of Labneh treatments. The most acceptable treatment was T3 that was made by adding L. plantarum. On the other hand, total solids, fat, total protein contents, titratable acidity, texture parameters, viscosity increased slightly during the storage period, while pH values were decreased. The counts of probiotic bacteria of Labneh treatments those made by adding these bacteria, even at the end of storage period were higher than the numbers should be present in food products to achieve their health benefits. Therefore probiotic Labneh could be a good vehicle for delivering the probiotic bacteria to consumers. On the other hand incorporation of mandarin oil in Labneh treatments caused a slight increase of total solids, fat, and lactose content, while decreasing the titratable acidity, acetaldehyde and diacetyl content of Labneh treatments and this increase or decrease was proportional to the rate of adding mandarin oil. Also, values of hardness, cohesiveness, springiness, gumminess, chewiness, and the viscosity of Labneh treatments decreased by adding mandarin oil especially above 0.2%. On the other hand, T1 that was made by 0.1% mandarin oil was the most acceptable Labneh treatments and gained the highest scores of organoleptic properties and was not significantly different from T2 that was made with adding 0.2% mandarin oil, while increasing the rate above that caused a significant reduction of the scores of organoleptic properties.