Master of Science (MS)


Animal Science (Animal, Dairy, and Poultry Sciences)

Document Type



Pulsed electric field processing represents a promising non-thermal technology which involves the application of pulses of high voltage (20-80 kV/cm) for less than one second to fluid foods placed between two electrodes. During the application of certain PEF conditions microbial inactivation occurs by causing a pore formation and destruction of the cell membranes. Lactobacillus acidophilus is an important probiotic bacterium used for the production of fermented dairy products. The objective of this study was to study the influence of pulsed electric field (PEF) on the growth characteristics, bile tolerance, acid tolerance, and protease activity of Lactobacillus acidophilus LA-K. Freshly thawed Lactobacillus acidophilus LA-K was suspended in peptone and treated in a pilot plant PEF system (OSU-4M). The treatments were pulse width (3, 6 and 9 µs), pulse period (10,000; 20,000 and 30,000 µs), voltage (5, 15 and 25 kV/cm) and flow rate (10, 60 and 110 mL/min). Control was run through PEF system at 60 mL/min without receiving any pulsed electric field condition. Growth and bile tolerance on control and treatment samples were determined hourly throughout 16 hours of incubation. Acid tolerance was determined at 0, 5, 10 and 15 minutes of incubation. Protease activity was determined at 0, 12 and 24 hours of incubation. The experimental design was a repeated measure design. Data were analyzed using the PROC GLM of the Statistical Analysis Systems (SAS). Differences of least square means were used to determine significant differences at P < 0.05 for main effects (pulse width, pulse period, voltage, flow rate) and interaction effects (pulse width * time, pulse period * time, voltage * time, and flow rate * time). Bipolar pulse width and pulse period significantly lowered acid tolerance and bile tolerance as well as slowed log stage growth of Lactobacillus acidophilus LA-K. Voltage significantly influenced acid tolerance, bile tolerance and growth of Lactobacillus acidophilus LA-K. Bipolar pulse width, pulse period and voltage did not influenced protease activity of Lactobacillus acidophilus LA-K. Flow rate significantly influenced bile tolerance and growth of Lactobacillus acidophilus LA-K. Flow rate did not significantly influenced acid tolerance and protease activity of Lactobacillus acidophilus LA-K.



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Committee Chair

Kayanush J. Aryana