Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


osu1339786533.pdf (1.44 MB)

ETD Abstract Container

Abstract Header

Effect of Electric Field on Growth Kinetics of Yogurt Starter Cultures, Lactobacillus bulgaricus and Streptococcus thermophilus

Costello, Seth Robert
http://rave.ohiolink.edu/etdc/view?acc_num=osu1339786533

Abstract Details

2012, Master of Science, Ohio State University, Food Science and Technology.
Fully understanding how electric fields stimulate microbial growth could have huge implications in the food industry, especially the fermented food industry. More research is needed to determine how electric fields interact with microorganisms and what conditions cause a stimulating effect. The objective of this research was to evaluate the effects of various electric fields, including moderate electric field (MEF) and pulsed electric field (PEF), on the growth kinetics of various lactic acid bacteria in order to expand upon research that was previously limited to only Lactobacillus acidophilus. Common yogurt starter cultures, Lactobacillus bulgaricus and Streptococcus thermophilus, were subjected to MEF during fermentation in de Man Rogosa Sharpe (MRS) broth. The electric field strength remained constant throughout all experiments at 1 V/cm. Two vessels were created to allow for side by side fermentation comparison. One vessel was ohmically heated by passing a current through the MRS broth and the other vessel was heated conventionally using a heated water jacket. Fractions of the fermentation over time were collected for microbial enumeration as well pH measurement. Fermentation by S. thermophilus at 35°C with 45Hz MEF showed a reduced lag time of 2 hours 6 minutes as compared to the control which had a lag time of 2 hours 45 minutes. Increasing the temperature or frequency resulted in loss of the reduced lag time for S. thermophilus. L. bulgaricus showed no significant difference in growth or pH between the control and all treatments. The effect of pulsed electric field on the growth kinetics of various strains of lactic acid bacteria (LAB) was also investigated. Two fermentation vessels (for treatment and control) were filled with MRS broth and held at either 25°C or 35°C. The broth was inoculated with L. bulgaricus, S. thermophilus, or Lactococcus lactis (L. lactis) and was exposed to PEF at strengths ranging from 2-10 kV/cm during fermentation. Fractions of the fermentation collected over time were plated for microbial enumeration, tested for pH, and in the case of L. lactis, assayed for bacteriocin production. There was no growth stimulation effect observed for any culture at the conditions tested in these experiments. A general trend of reduced growth was seen as electric field was increased for both S. thermophilus and L. bulgaricus. It was hypothesized that L. lactis may produce the bacteriocin nisin at an increased rate due to cell stress and self induction from pore formation caused by the PEF treatments, but the opposite was found. The control produced nisin slightly faster showing the first clearing zone (200 arbritrary units) at 10 hours with the treated showing the first clearing zone (200 arbritrary units) at 11 hours. Although a stimulation effect was not observed in these experiments, further research utilizing differing treatment parameters would be needed in order to claim that mild PEF does not cause the stimulation of bacterial growth.
Ahmed Yousef, Dr (Advisor)
Sudhir Sastry, Dr. (Committee Member)
Luis Rodriguez-Saona, Dr. (Committee Member)
73 p.
Food Science

Recommended Citations

Citations

  • Costello, S. R. (2012). Effect of Electric Field on Growth Kinetics of Yogurt Starter Cultures, Lactobacillus bulgaricus and Streptococcus thermophilus [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1339786533

    APA Style (7th edition)

  • Costello, Seth. Effect of Electric Field on Growth Kinetics of Yogurt Starter Cultures, Lactobacillus bulgaricus and Streptococcus thermophilus. 2012. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1339786533.

    MLA Style (8th edition)

  • Costello, Seth. "Effect of Electric Field on Growth Kinetics of Yogurt Starter Cultures, Lactobacillus bulgaricus and Streptococcus thermophilus." Master's thesis, Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1339786533

    Chicago Manual of Style (17th edition)

osu1339786533
2,362
© 2012, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.