Type of Document Master's Thesis Author Muramalla, Tanuja Author's Email Address email@example.com URN etd-06052010-111924 Title Influence of Low Homogenization Pressures on Acid Tolerance, Bile Tolerance, Protease Activity, and Growth Characteristics of Lactobacillus delbrueckii ssp bulgaricus LB-12, Streptococcus salivarius ssp thermophilus ST-M5 and Lactobacillus acidophilus LA-K Degree Master of Science (M.S.) Department Dairy Science (Animal, Dairy, & Poultry Sciences) Advisory Committee
Advisor Name Title Aryana, Kayanush J. Committee Chair Boeneke, Charles A Committee Member Ge, Beilei Committee Member Keywords
- beneficial micro organisms
Date of Defense 2010-05-12 Availability unrestricted AbstractLactobacillus 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.
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