6: Pulsed Light Processing

Question 1

Describe pulsed light processing.

Answer 1

• In PL processing, inert gas lamp converts short, high power electric pulses into short duration, high power pulses of radiation.
• Some energy is reflected, other penetrate into the food and get refracted, reflected, scattered and absorbed.

Question 2

What are the factors affecting the penetration and reflection of pulsed light?

Answer 2

• Wavelength of light
• Composition of food
• Structure of food

Question 3

Describe the components of a pulsed-light processing equipment.

Answer 3

Electrical unit: Continuous low power electrical energy is collected in capacitors and released as pulsed, high power electrical energy.

Lamp: The lamp converts high power pulsed electric energy into high power pulsed light

Treatment chamber: Holds the food to receive PL treatment.

Auxiliary equipment: System for data acquisition and cooling control.

Question 4

How does PL affect MO?

Answer 4

Inactivates MO via:

Photochemical mechanism:
- Conjugated double bonds (C=C) of proteins and nucleic acids absorbs photons from PL
- Cleavage of bonds occurs and structure of DNA changes.
- Production of photoproducts inhibits DNA replication
- Mutation and damages to the genome causes cell death.

Photothermal mechanism:
- MO absorbs PL, energy dissipates as heat.
- Localized rapid heating causes cell rupture and cell death.

Question 5

What are the advantages of PL instead of continuous?

Answer 5

• Higher power at the same energy level
• Shorter time of thermal conduction
• Energy saving
• Deeper penetration
• More lethal towards MOs by
  1. Causing extensive, unrepairable damage
  2. inactivating repair enzymes
  3. Generating germicidal chemicals such as OH radicals, ozone, and
  H2O2

Question 6

What are the effects of PL on food?

Answer 6

• Color change
• Nutrient degradation
• Increased lipid peroxidation
• Texture change
• Odor change

Question 7

Describe the factors that may affect the efficiency of PL processing.

Answer 7

• Type of radiation (Pulsed is more efficient than continuous)
• Wavelength of light (UV is more effective than Vis and IR)
• Temperature (high temperature promotes microbial inactivation but reduces lifespan of lamp and cause thermal damage)
• Intensity (FDA: Should not exceed 12J/cm2)
• Product parameters:
  (Food with reflective surface should be coated with absorption enhancing agents to increase eff.; use thin-film flow unit and turbulent reactor to process foods with solid suspension, high fat and protein.)