Master of Science (MS)


Dairy Science (Animal, Dairy, and Poultry Sciences)

Document Type



Consumers are becoming conscious of their diet, increasing protein intake and avoiding carbohydrates and fats. Whey proteins have branch chain amino acids responsible for muscle building. Whey protein isolate (WPI) contains more than 90% protein. The effect of incremental addition of WPI on probiotic characteristics of pure cultures and cultures in yogurt and yogurt characteristics are not known. The hypothesis was that “added” WPI will influence the characteristics of yogurt culture bacteria in pure form and in yogurt. The objectives were: to determine the influence of added WPI on (1) acid and bile tolerance, growth and protease activity of pure cultures Streptococcus thermophilus ST-M5 and Lactobacillus bulgaricus LB-12, (2) growth, acid and bile tolerance of starter culture from manufactured plain yogurt, (3) the physico-chemical characteristics of yogurt over its shelf life and (4) the sensory attributes of yogurt. WPI was used at 0, 1, 2 and 3% w/v. Acid tolerance was conducted on pure cultures and cultures from manufactured plain yogurt at 30 minutes intervals for 2 hours of incubation and bile tolerance at 1 hour intervals for 5 hours. Yogurt was manufactured using 0 (control), 1, 2 and 3% WPI. For sensory evaluation, blueberry yogurt was manufactured using the same WPI concentrations. Physico-chemical analyses of yogurts were conducted every 7 days during 35 days of storage. Enumeration of yogurt cultures during yogurt´s shelf life was evaluated at 7, 21 and 35 days of storage. Sensory evaluation was conducted on yogurt 7 days after its manufacture. Data were analyzed using Proc Mixed model of SAS® 9.3 program and by analysis of variance (ANOVA) using Proc GLM. Significant differences between means were analyzed at α = 0.05 using Tukey´s adjustment. Use of 2% WPI improved acid tolerance of Streptococcus thermophilus ST-M5 in yogurt. Use of 2 and 3% WPI improved bile tolerance of Lactobacillus bulgaricus LB-12 over the 5 hours of incubation. WPI decreased syneresis of yogurts and improved sensory attributes of flavored yogurt. Overall liking scores were higher for 1% WPI yogurts compared to control. Overall, 1 or 2% WPI can be recommended in manufacture of higher whey protein yogurts.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Aryana, Kayanush J.



Included in

Dairy Science Commons