It enhances our knowledge in the field of non thermal technology for food preservation and effect of non thermal technology on microorganisms.

1. EFFECT OF NON THERMAL PROCESSING
METHODS ON MICRO ORGANISMS
Presented by:
Ms. Jenjen Golmei
Process food engineering

2. CONTENTS
• Introduction
• Non thermal technologies
• Pulse electric field processing
• Effect on microorganisms by PEF
• Ultra violet radiation
• Effect on microorganisms by UV
• Conclusions

3. INTRODUCTION
Food processing
Is needed to
• Ensure safety (kill micro organism)
• Increase shelf life
(destruction of enzymes, toxin)
• Add value
(texture, flavor and color)
• Make new products
Preservation processes can be
• Thermal processing
• Non thermal processing

4. NON THERMAL TECHNOLOGY
• Effective at ambient or sub lethal temperatures
• Minimal use of energy.
• Retention of desired qualities and nutritional
parameters.
• Improve shelf life.
• Temperature rise may be expected or even may be
desired.
• May be employed for both solid and liquid foods.
• High hydrostatic pressure, Pulsed electric field,
ultrasound, pulsed light, Irradiation, Electron beam,
Oscillating magnetic field, Ozone, Gas, Plasma.

5. PULSED ELECTRIC FIELD (PEF)
PROCESSING
• Application of high voltage pulses to foods placed
between two electrodes.
• 10 to 80 kV/ cm
• 1- 100 µs
High intensity PEF
• 10 to 80 kV/ cm
• 10- 10000 µs

6. MICROBIAL INACTIVATION MECHANISM
• Damage to cell membrane.
• Electropermeabilization – shrinkage and leakage of
intracellular content.
• Electroporation – formation of pores of cells and
organelles (Zimmermann, 1986).
- Compression is exerted by the accumulation of free
charges at both sides of the membrane reducing the
thickness of cell membrane.
- Viscoelastic forces oppose the electro-compression
of the membrane.

8. - When transmembrane potential > 1V,
electrocompressive force exceeds viscoelastic force.
- Number and sizes of pores depend on electric field
strength and treatment time.
- Electropermeabilization is reversible if electric field
intensity < threshold electric field (Ec) and or
treatment time is short.
• Dipolar orientation of the phospholipids within the two
monolayers of the membrane (Hamilton, 1968).
• Structural defects in membrane consisting of
spontaneous pores that expand when electric exceeds
critical transmembrane potential (Tsong, 1991).

10. EFFECT OF PEF ON MICROORGANISMS
Factors affecting effectiveness
• Process factor: can be modified at will or dosed.
1. Electric field strength (E)
• Critical intensity (Ec) must be reached.
• E> Ec, exponential effect on microbial
inactivation.
• E must be kept low.
2. Treatment time
• Short pulses are applied to avoid excessive
heating or undesirable electrolyte reactions.
• Pulse width * no. of pulse applied.

11. • Pulses between 1- 5 µs produce best results for
microbial inactivation.
• After E is applied,10 ns required to establish a
transmembrane potential.
• After pore formation, 1- 5 µs required to allow
expansion of pores to a critical diameter.
3. Pulse shape
• Exponentially decaying pulses and square pulses.
• Bipolar for both pulses are more effective than
mono polar.
• Instant – charge- reversal pulses have enhanced
effectiveness.

12. • Biological factors
1. Shape and size of microorganisms
Vc= f*Ec*a*cosʋ f= l/(l- d/3)
2. Types of microorganisms
Sensitivity to PEF: yeasts> Gram –ve bacteria > Gram
+ve bacteria > spores
3. Physical state of microorganisms
• Growth : initial lag phase exponential or
logarithmic phase stationary phase death
phase.
• Sporulation:
Reproductive method yeasts and molds
protective method bacteria

13. • Product factors
1. Composition
Conductivity, pH or presence of antimicrobials,
dielectric strength, ionic strength, presence of
components such as protein and lipids.
2. Temperature
• Synergistic effect up to 65 ᵒC
• For lipid- protein membrane:
• Breakdown voltage at 4 ᵒC= 2 V
20 ᵒC= 1V
30- 40 ᵒC= 500 mV (up to 1µs)
.

14. Microorganism Food Treatment
conditions
Microbial
reductions
Reference
Escherichia
coli
Apple juice E= 30 kV/cm
τ= 4µS,T= 25 ᵒC
5 Evrendilek et
al., 2000
Apple juice E= 31 kV/cm
τ= 4µS, T=10 ᵒC
2.6 Evrendilek and
Zhang, 2005
Skim milk E= 24 kV/cm
τ= 2.8 µS, T=10 ᵒC
1.96 Evrendilek and
Zhang, 2005
Saccharomyces
cerevisiae
Apple juice E= 20 kV/cm
τ= 2 µS, T= 30 ᵒC
4 Cserhalmi et
al., 2002
Orange juice E= 35 kV/cm
τ= 4 µS, T= 39 ᵒC
5.1 Elez- Martinez
et al., 2004
Pseudomonas
flourescens
Skim milk E= 60kV/cm
τ= 210 µS, T= 50 ᵒC
8 Jung et al.,
2000
Table. 1: Effect of PEF on microorganisms in fluid foods

15. Staphylococcu
s aureus
Liquid whole
egg
E= 40 kV/cm
τ= 3 µS, T= 20 ᵒC
3 Monfort et al.,
2010
Green tea
beverage
E= 40 kV/cm
τ= 3 µS, T= 20 ᵒC
4.9 Zhao et al., 2008
Listeria
innocua
Skim milk E= 30- 40 kV/cm,
τ= 3 µS, T= 37 ᵒC
2.5 Fernandez-
Molina et al.,
2006
Skim milk E= 41 kV/cm
τ= 2.5 µS, T= 37 ᵒC
3.9 Dutrusux et al.,
2000
Lactobacillus
plantarum
Orange juice E= 35 kV/cm
τ= 4 µS, T= 32 ᵒC
5.8 Elez- Martinez et
al., 2006
Fruit juice- soy
milk beverage
E= 35 kV/cm
τ= 4 µS, T= 32 ᵒC
5 Morales-de la
peṅa et al., 2010
E= field strength, T= process temperature ,τ= pulse width, n= no. of
cycles

16. ULTRAVIOLET RADIATION

17. MICROORGANISM INACTIVATION BY UV
RADIATION
• Ultra violet radiation (UV)
a. UVA (315- 400 nm)
b. UVB (280- 315 nm)
c. UVC (200- 280 nm)
• UVC is called germicidal UV.
• Most organism absorb UV light at 254 nm wavelength.
• Inactivate microorganism by breaking bonds in
deoxyribonucleic acid (DNA).
• Constituent bases of DNA : adenine, cytosine, guanine
& thiamine.

18. • Absorption of UV photon results in photochemical
dimerization of thymine pairs.
• If enough pairs are form, DNA cannot be replicated.
• Resistance to UVC treatment is determined by
ability to repair DNA damage caused by UV.
Gram- negatives< Gram- positives< yeast< bacterial
spores< molds< viruses.
Protozoa : most resistant to UV than other
organisms.
• Cells in logarithmic phase are more sensitive to UV.

19. • UV dose: represents the UV exposure of a given
organism in the germicidal range.
• Factors:
– Flow rate
Product flow must be turbulent with minimum
Reynolds number of 2200.
– Type of liquid
Transmitivity, color, turbidity, absorption
coefficient and path length.
I =Io exp( α d)

20. – Type and number of organisms
Cell wall structure, thickness, and composition;
presence of UV absorbing proteins; or differences
in the structure of the nucleic acids themselves.
Most bacteria, viruses and yeasts =100 J/m2 or
less.
Molds and molds spores= 450- 600 J/m2
• UV doses required for reducing populations of
microbial groups by a single order of magnitude a
quantity referred to as the D value.

21. Table. :UV inactivation doses (mJ/cm2) measured at 253.7 nm for
various microbial groups
Microbial group D value (mJ/cm2)
Enteral bacteria 2 to 8
Cocci and micrococci 1.5 to 20
Spore formers 4 to 30
Enteric viruses 5 to 30
Fungi 2.3 to 8
Protozoa 30 to 300
Yeast 60 to 120
Algae 300 to 600
Deinococcus radiodurans: Most UV-resistant bacteria isolated to date.
D value = 19.7 to 145 mJ/cm2

22. • Inactivation kinetic
– Represented as survival curve or a dose response
curve.
– UV treatment follows first order inactivation
kinetics.
– Shape of survival curve is sigmoid.
– Injury phase
– Survivors rapidly decline
– Tailing phase
– For some bacterial cells, photoreactivation may
occur.

23. Table. :Radiant exposure of UV (250 nm) for 4 log reduction:
Microorganism Exposure required (J/m2 )
Without
photoreactivation
With photoreactivation
Citrobacter freundii 80 250
Enterobacter cloacae 100 330
Enterocolitica faecium 170 200
Escherichia coli 50- 170 188- 280
Pseudomonas aeruginosa 110 190
Salmonella typhi 140 190
Salmonella typhimurium 130 250
Vibrio cholera 50 210
Klebsiella pneumoniae 110 310

24. CONCLUSIONS
PEF
• More research is needed.
• Differential microbial resistance to PEF due to intrinsic
microbial characteristics.
• Spores are resistant to PEF treatment.
UV radiation
• Disinfection by application of electromagnetic energy
to organism’s genetic cellular material.
• Lethal effect is cell inability to replicate.
• Effectiveness is direct function of UV dose of the
organism.

25. REFERENCES
• Gustavo V, Tapia S and Cano M. (2005). Novel food
processing technologies.
• Cullen P J, Tiwari K and Vasilis P. (2012). Novel
thermal and non thermal technologies for fluid foods.
• Hussain et al. (2014). Impact of non thermal
processing on the microbial and bioactive content of
foods. Global journal of biology, agriculture and
health sciences. Vol. 3(1): 153- 167.
• Gayan et al. (2013). Biological aspects in food
preservation by ultra violet light. Food bioprocess
technology.(2014) 7:1- 20

26. Thank you