Master of Science (MS)


Dairy Science (Animal, Dairy, and Poultry Sciences)

Document Type



Lactobacillus delbrueckii ssp bulgaricus LB-12, Streptococcus salivarius ssp thermophilus ST-M5 and Lactobacillus acidophilus LA-K are dairy cultures widely used in the fermentation of dairy products. Homogenization is an essential process in dairy industry for making several products. High homogenization pressures (>50 MPa) are used to create stable emulsion, inactivate the pathogens and increase the protease activity of dairy cultures. Sparse literature is available on the influence of low homogenization pressures, and their effect on beneficial characteristics of dairy cultures is not well understood. The objective of this study was to determine the effect of low homogenization pressures on acid tolerance, bile tolerance, protease activity and growth characteristics of the three dairy cultures. The cultures were individually inoculated in cool autoclaved skim milk (4 C) and subjected to homogenization pressures of 0 MPa/ 0 psi (control), 3.45 MPa (500 psi), 6.90 MPa (1000 psi), 10.34 MPa (1500 psi) and 13.80 MPa (2000 psi) for 5 continuous passes. Growth and bile tolerance of samples were determined hourly for 10 hours; acid tolerance was determined every 20 minutes for 120 minutes; and protease activity was determined at 0, 12 and 24 hours of incubation. The experimental design was repeated measurements on complete randomized block. Data were analyzed using proc mixed model of statistical analysis system (SAS). Differences of least square means were used to determine significant differences at p<0.05 for main effect (homogenization pressure) and interaction effect (homogenization pressure * time). All low homogenization pressures improved acid tolerance of Lactobacillus delbrueckii ssp bulgaricus LB-12 but had no effect on protease activity and had negative effect on growth and bile tolerance of the bacterium. Low homogenization pressure of 6.90 MPa (1000 psi) improved the acid tolerance, bile tolerance, and protease activity but homogenization pressures had no effect on growth of Streptococcus salivarius ssp thermophilus ST- M5. Low homogenization pressures of 13.80 MPa (2000 psi), 6.90 MPa (1000 psi) improved acid tolerance, bile tolerance respectively of Lactobacillus acidophilus LA-K but had no effect on protease activity and growth of the bacterium. Some low homogenization pressures positively influenced some characteristics of the three dairy cultures.



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