4: Pulsed Electric Field

Question 1

Describe pulsed electric field processing.

Answer 1

• High voltage electric field is applied to a substance for several microseconds
• Used for electroporation: Formation of pores increase cell membrane permeability, which induce stress reaction and improve mass transfer. As a result secondary metabolites are produced and extractability increases.
• PEF can also e used to breakdown cell membrane and inactivate microorganisms.

Question 2

Describe the 4 stages of electroporation.

Answer 2

(TPER: Time to Party, Everyone Ready!)

Stage 1: Transmembrane potential is increased
When high voltage electric is applied, charges with opposite polarity accumulated at both sides of the membrane. Electrical potential difference develops across cell membrane.

Stage 2: Pores formation
Transmembrane potential reaches critical transmembrane potential which leans to membrane permeabilization through the electromechanical model and statistical model.

Stage 3: Evolution of pore size and number
TAT (Time, Amplitude and Temp) affects pore size and number.

Stage 4: Recovery of cell membrane’s integrity.
1. Fast process: Reduction of pore size (Microseconds to minutes)
2. Slow process: Complete sealing (minutes to hours)

Question 3

Explain the electromechanical model and statistical model.

Answer 3

Both are models for explaining electroporation.

Electromechanical model:
When electric field is applied, charges of both side of the membrane reorganizes. The transmembrane potential (voltage difference) increases, causing the attraction of opposite charges. This leads to deformation of cell membrane and develop electro-compression forces. Permeability is increased and pores are formed

Statistical model:
When hydrophobic pores form due to thermal fluctuation, pore radius increases over time due to the increase of temperature and transmembrane potential. Once the critical radius is reached, the hydrophobic pores converts into hydrophilic pore.

Question 4

What is the critical electric field strength?

Answer 4

The electric field strength required to cause the formation of pores in a cell.

Question 5

What are the parameters to be controlled for PEF?

Answer 5

• Electric field strength
• Time, specific energy and pulse geometry
• Treatment temperature
• Treatment medium (e.g., Conductivity, pH, Airbubbles/particles
• Cell characteristics (endospores do not respond to PEF)

Question 6

What are the applications of PEF?

Answer 6

• Low intensity PEF induce stress without killing the microorganisms to induce the secretion of secondary metabolites and improve extraction yield.
• Disintegration of cells. High intensity PEF induce permanent damage to cells, which improve extraction efficiency at shorter time.
• Microbial and enzyme inactivation. High electric field strength is used in combination with thermal treatment to inactivate endospores.

Question 7

What are the 2 main components of PEF system?

Answer 7

• Impulse generation system: Transform electrical power to pulsed high intensity electric
• Treatment chamber: to contain foods.