[Study of the prolongation possibility shelf-life of local yoghurt]

This study was conducted to prolong the shelf life of Yoghurt through the use of some kinds of additions or changing the technical terms of manufacturing. Chemical, microbial and sensory analyses of yoghurt samples during storage periods at 4±1°C and 10±1°C . The experiments were conducted as multiple times,and the results were analyzed statistically. All samples were manufactured using raw milk with good chemical and microbial qualities. The milk was Pasteurized in sterile containers 1kg each with tight lids for 20 minutes at 90°C then cooled down to 44±1°C,and the milk was vaccinated starter at a rate of 3%. All the samples were later incubated at 45 ±1°C for 4 hours in order to get a coherent thrombous with pH varying from 4.6 to 4.7. After the process of incubation,all samples were cooled down to 4°C. Then the yoghurt samples were stored at 4°C and at 10°C. When lactulose is added at rates of 3%,4% and 5% during a storage period of 42 days at 4±1°C and 10±1°C, the results of the analysis the microbial characteristics show that the vital force for the Starter has lasted for 7 days in the standard sample, 28 days in the sample containing 3% lactulose, 35 days in the sample containing 4% and 42 days in the sample containing 5% lactulose if the samples are stored at 4±1°C. No significant difference is observed in the results when samples are stored at 10±1°C. In addition,results have proved that adding lactulose does not affect the initial pH levels of yoghurt, and the values of the sensory characteristics of Yoghurt have decreased during the storage period. It has also been shown that the standard sample can be considered practically fit for consumption during 7 days of storage,whereas Yoghurt samples containig lactulose remain fit for consumption for 42 days of storage. When garlic rates 0.05%, 0.075% and 0.1% are added during a 50 days storage period at 4±1°C and 10±1°C, the results of the analysis of microbial characteristics have shown that the vital force of the Starter has lasted for 7 days in the standard sample, 35 days in the sample containing 0.05% garlic, 42 days in the sample containing 0.075% garlic, and 49 days in the sample containing 0.1% garlic when samples are stored at 4±1°C . No significant difference is observed in the results when samples are stored at 10±1°C. Meanwhile, the results of the analysis of the sensory characteristics show that Yoghurt containing 0.05% of garlic is more preferred than that containing higher rate due to the absence of taste and smell of garlic in the sample. Moreover,the results have indicated that the addition of garlic the does not affect the initial pH levels of yoghurt,and the values of the sensory characteristics of Yoghurt have decreased during the storage period. It has also been conducted that the standard sample can be considered fit for consumption for 7 days of storage, whereas the samples of Yoghurt containing garlic can be fit for consumption during 49 days of storage.