Inactivation of Saccharomyces cerevisiae and Candida humilis in Potassium Phosphate Buffer by Pulsed Electric Fields

• Author / Creator

  Ou, Qixing

• Pulsed electric field (PEF) is a promising athermal food preservation technology, having the potential to provide a better balance between food safety and food quality. But the high cost of PEF treatment has limited the commercial application of this technology. The aim of this MSc thesis research was to determine the effect of different parameters on the efficacy of PEF. A custom-built PEF system with a gap distance of approximately 14 µm between two parallel plate electrodes was used to provide a homogeneous electric field and temperature distribution. Saccharomyces cerevisiae and Candida humilis were used as model microorganisms, and potassium phosphate buffer was used as a model fluid. Viable cell enumeration after PEF treatments in the presence or absence of 100 µM of propidium iodide was used to distinguish reversible and irreversible electroporation. The electrical parameters governing the efficacy of PEF include pulse shape, pulse width, pulse frequency, electric field strength, and specific energy input. Experiments were designed in a systematic way with the variation of field strength from 18 to 71 kV/cm, specific energy input from 8 to 46 kJ/kg, pulse width from 86 ns to 4 µs, pulse frequency of 5 and 10 kHz, and pulse wave shapes of unipolar square pulse and bipolar exponential pulse. Results demonstrated that the specific energy input had the highest correlation (r2=0.84) with the lethal effect of PEF, followed by field strength (r2=0.10) and pulse width (r2=0.003). In order to avoid electrolysis during PEF treatments, alumina (Al2O3) covered gold electrodes were employed. Results indicate that conduction current was not necessary for electroporating and inactivating cells by PEF, but electrolysis had a strong synergy with PEF. The composition of fluid has the ability to greatly influence the efficacy of PEF.

• Subjects / Keywords

  • PEF
  • Saccharomyces-cerevisiae
  • Conduction Current
  • Efficacy
  • Propidium iodide
  • Electrolysis
  • Energy Input
  • Yeast

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3154DX2F

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.