Date

2017

Author

Değirmenci, Cansu

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Yogurt is a valuable functional food and has an important market worldwide. Yogurt is made by fermentation of milk with lactic cultures containing Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. Since yogurt contains viable bacterial cultures, its shelf life related to the viability of the cultures and lactic acid formation, is a critical problem for the food industry. In order to prevent undesirable effects of artificial additives, natural additives are preferred to prolong shelf life of yogurt. Natural additives such as milk powder, whey powder, lactose, inulin, casein, starch and others may be added to yogurt. The main objective of this study was to determine the effect of whey powder and probiotic encapsulated whey powder on the shelf life of yogurt, the viability of the yogurt bacteria and the probiotic bacteria.In the first part of the study, optimization of spray drying conditions for the encapsulation of probiotic Lactobacillus acidophilus in whey powder was done by Response Surface Methodology. Optimized conditions were found as 140°C for inlet temperature, 10 rpm for pump rate (with liquid flow rate of 0.485 L/h), and 0.83:0.17 for whey powder to arabic gum ratio. 48.36% production efficiency and 93.95% encapsulation efficiency were achieved in spray drying to produce probiotic encapsulated powder with optimized conditions. These whey powders were analyzed for the viability of probiotic cultures and their particle size distributions. The yield for viability of L. acidophilus in encapsulation was found as 95%. While the yield for viability of free L. acidophilus was found as 75.46%, the yield for viability of encapsulated L. acidophilus after being exposed to simulated gastrointestinal was found as 89.16%. The second part of the study consisted of yogurt analysis. Yogurt samples prepared with or without encapsulated probiotics and the shelf life was analyzed over 28 days of storage at 4°C. L. acidophilus can survive during 28 days of storage (as cell number 108 CFU/g) in yogurt containing encapsulated probiotic whey powder on the contrary to free cells cannot survive. At the end of 28 days of storage and even 50 days of storage, there was not seen mold and yeast formation in yogurt with whey powder. Sensory analysis showed that the addition of whey powder did not affect the yogurt properties negatively. 

Subject Keywords

Yogurt., Whey., Probiotics., Encapsulation., Lactobacillus acidophilus.

URI

http://etd.lib.metu.edu.tr/upload/12621310/index.pdf
https://hdl.handle.net/11511/26734

Collections

Graduate School of Natural and Applied Sciences, Thesis