PEF APPLICATIONS IN DAIRY TECHNOLOGY

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PEF APPLICATIONS IN DAIRY TECHNOLOGY

• M. BURCU KIZILÖZ
• 506051509

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CONTENTS

• General definition of PEF
• Microbial inactivation by PEF in dairy technology
• Enzyme inactivation by PEF in dairy technology
• Nutritional evaluations
• Hurdle approach and shelf life
• Conclusion

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INTRODUCTION

• Pulsed electric field is a nonthermal processing
  technology that may have the potential to replace
  traditional thermal pasteurization.
• PEF technology consists of the application of
  short duration (1100 µs) high electric field
  pulses (1050 kV cm) to a food placed between two
  electrodes.

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Inactivation mechanism

• The effect of PEF treatment on microorganisms is
  known as electroporation rather than the
  temperature increase or the electrolysis
  products.
• Electroporation is the formation of pores in
  cells and organelles.
• Free charges tend to accumulate in the inner and
  outer surface of the membrane generating a
  transmembrane potential of about 10 mV. When the
  external electric field exceeds a critical value
  or threshold, the membrane is unable to withstand
  the electrocompression and pores are formed.

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The effects of PEF treatment on inactivation of
microorganisms largely depend on process
conditions such as
Pulsed Electric Field

• electric field intensity
• pulse width
• treatment time
• Temperature
• pulse wave shapes

• microbial type, concentration, and growth stage
  of microorganisms
• treatment media

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Microbial Inactivation by PEF in Dairy Technology

• PEF had a partial effect on the inactivation and
  destruction of microorganisms in dairy products
  but the survivability of the cells differed
  according to treatment conditions and
  microorganism.

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Fleischmana, G. J. et al, 2004

• L. monocytogenes
• Number of pulses 550 pulses
• Electric field strength 1530 kV/cm
• Temperature 060C
• media bases water and skim milk

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Results

• 1 - Tlt 50C
• Water
• 1 log reduction
• Skim milk
• no reduction

• 2 - T 50C - 55C synergy between PEF and
  thermal energy
• addition of thermal energy
• contributed to the kill
• increased the susceptibility of L. monocytogenes
  to PEF

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Floury, J., 2005

• Effect of the combination of PEF with
  conventional heat treatment on the microbial
  inactivation Salmonella enteritidis
• Media UHT skim milk
• PEF
• 50 up to 3000 ns,
• electric field strength 30 to 80 kVcm1)
• pulse frequency 1 to 815 Hz
• volumetricflow rate 1 to 10 Lh1)
• Temperature
• 56, 57.5, 59,61 and 62 C.

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Experiment

• Experiment III
• Milk
• 59C preheated
• held for 38 s
• cooled

• Experiment I
• Milk
• 42 C preheated
• PEF treatment (temperature rise to 62 C)
• held for 38 s
• cooled

• Experiment II
• Milk
• 42 C preheated
• PEF treatment (temperature rise to 62 C)
• cooled

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Results

• Combination of PEF and heating was more effective
  than each on its own but additive rather than
  synergistic
• different responses to the various stresses
  applied to the microbial Salmonella enteritidis
  species
• continuous heat processing 1.7 log
• PEF processing 1.2 0.3 log
• the combination of the two operations 2.3 0.4
  log

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Evrendilek, G. A., 2004

• Media Skim milk
• PEF
• Circulation chamber
• Stepwise modes
• Duration 3-7 µs
• 250Hz pulse repetition rate
• 1ml s-1flow rate
• 460 µs total treatment time
• 35kVmm-1 electric field strength
• Survivals of PEF-treated S. aureus cells were
  also
• kept at refrigeration temperature for 2 weeks.

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Results

• PEF application
• Stepwise mode 3,7 log cfu/ml reduction
• Circular flow 3 log cfu/ml reduction
• The difference between two systems was not
  significant.
• By the end of the second week ? a significant
  reduction in the S. aureus cells treated by PEF
• During PEF some of the cells might be inactivated
  but the rest might be only weakened
  refregiration

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Enzyme inactivation by PEF in dairy technology

• Milk and dairy products may contain
  psychrotrophic microorganisms, which can cause
  important problems in the dairy industry since
  they can grow and maintain activity even at
  refrigeration temperatures. These species may
  produce enzymes, such as
• lipases ? rancid flavor
• Proteases ?degrade caseins, increases nitrogen
  content in the whey and reduce milks thermal
  stability
• PEF cause changes in the enzyme configuration to
  reach denaturation
• alteration in the enzyme shape
• the substrate could not fit the active site
• prevent conversion of the substrates into
  products

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Castro, A. J. et al., 2001

• Alkaline phosphate (ALP?an indicator of the
  adequacy of thermal pasteurization of milk )
• Media
• raw whole milk
• 2 milk
• nonfat milk
• modified simulated milk ultrafiltrate
• Electric field intensities18.8 and 22.0 kV/cm
• 0-70 pulses

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Result

• The activity of ALP was reduced by 65 in milk
  and MSMUF
• 59 in raw milk and pasteurized, homogenized 2
  milk
• The temperature of
• milk treated with 70 pulses of 21.8 kV/cm
  increased from 22?C to 43.9?C
• MSMUF treated with 70 pulses of 22.3 kV/cm
  increased from 4?C to 8.4?C
• The increase in temperatures did not affect the
  inactivation of ALP

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Result

• The maximum inactivation of ALP was 65.
• The inactivation of ALP is directly related to
  the concentration of the ALP, to the intensity of
  the electric field and to the number of pulses.

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Bendicho, S. et al., 2003

• Protease from Bacillus subtilis.
• Samples were subjected to HIPEF treatments of at
• field strengths from 19.7 to 35.5 kV/cm
• pulse width (4 and 7 µs)
• pulse repetition rates (67, 89, and 111 Hz)
• Media skim and whole milk

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Results

• Protease activity decreased with increased
  treatment time or field strength and pulse
  repetition rate.
• Pulse width ? no differences were observed
  between 4 and 7 µs pulses when total treatment
  time was considered.
• 4-µs-pulse-width process requires alot more
  pulses than the 7-µs pulse width
• Milk composition affected the results since
  higher inactivation levels were reached in skim
  than in whole milk.
• The higher the frequency pulse rate the higher
  the inactivation

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Results

• At the lower frequency (67 Hz) ? no significant
  differences among the inactivation with SM or WM
• At intermediate frequencies(89 Hz) and at the
  highest frequencies (111 Hz) ? the inactivation
  with WM was lower than that with SM
• Fat content
• 866-µs treatment at 89 Hz
• WM up to a 38.9 inactivation
• SM up to 64.4 inactivation

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Nutritional evaluations

• Some studies are conducted to examine the loss of
  vitamins with PEF compared to conventional
  heating

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Bendicho, S. et al., 2002

• Media milk and simulated milk ultrafiltrate
• PEF treatments of up to 400 µs at field strengths
  from183 to 271 kV/cm
• Heat treatments
• Low heat treatment 63 C-30 min
• High heat treatment 75 C-15 s

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Results

• No changes in vitamin content were observed
  except for ascorbic acid for both treatment
• Ascorbic acid at milk gt ascorbic acid at SMUF
• PEF? 934
• Low heat pasteurisation treatments ? 497
• High heat pasteurisation treatments ? 867

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PEF with Hurdle Approach

• PEF can be applied with other novel or
  conventional preservation techniques.
• Synergic
• Cummulative
• Antagonistic

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Fernandez, J. J. et al., 2005

• Media Raw skim milk
• PEF alone
• at 40 kV/cm
• 30 pulses
• Duration 2 ms duration each,
• Combining thermal processing
• at 73 or 80C for 6 s followed by a PEF process
  at 50 or 30 kV/cm, 30 pulses at 4 or 3 Hz.
• Microbiological quality of the skim milk was
  monitored for 14, 22 and 30 days at 4C

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Results

• unprocessed skim milk 7.6 log cfu/mL
• On day 14, the PEF-processed skim milk
• 10 pulses ? 7.2 log cfu/mL
• 20 pulses ? 6.5 log cfu/mL
• 30 pulses ? 6.3 log cfu/mL
• Combination of thermal/PEF-processed skim milk
• 22 days ? 4.1 log cfu/mL (acceptable)
• 30 days ? 4.9 log cfu/mL (acceptable)

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Results

• A synergistic effect at 73 and 80C when
  processed with 50 or 30 kV/cm.
• first heating the milk to induce physical and
  chemical damage to the cell membranes
• PEF processing facilitates the entrance of the
  electrical pulses to the interior of the
  bacterial cell membranes.

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• Shelf life

• Total bacteria count

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SEPUÂ LVEDA-AHUMADA, D. R. et al., 2000

• Textural properties (hardness, springiness,
  cohesiveness, and adhesiveness) and sensory
  attributes of Cheddar cheese made with
• heat-treated milk
• 63C for 30 mins when using LTLT
• 72C for 15 s for the case of HTST ),
• PEF-treated milk (E35 kV/cm, N30 pulses)
• untreated milk

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Results

• Heat treatments produced lower final counts of
  mesophile flora than PEF
• lower effectiveness of pulses

• 0 total coliform bacteria ? differences in the
  cell membrane

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Results

• Adhesiveness milk pasteurized by LTLT ?highest
• Cohesiveness thermally treated ? greater
• Springiness Hardness milk pasteurized by any
  method harder than those made from untreated milk
  

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Gallo, L. I. et al., 2006

• The combination of nisin and (PEF) on Listeria
  innocua
• Media liquid whey protein concentrate (LWPC)
• Nisin treatment 30 min 7C, 25-50 IU/ml
• PEF treatment
• 60 pulses, at 12 kV/cm of electric field
  intensity with 3 µF capacitance and 0.2 ms/pulse
  time decay (s)
• Combined treatment
• NB nisin before PEF
• NS simultaneously
• NA nisin after PEF

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RESULTS

• NB ? additive or slightly synergistic(esp. at low
  nisin concentrations)
• NS ? antagonistic
• ! Treatment sequence is important

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CONCLUSION

• The use of PEF technology in foods reduces
  pathogen levels while increasing shelf life
  retaining original flavor, color, and nutritional
  properties in dairy products
• The inactivation mechnaism is dependent on many
  factors and may be used with other technologies

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CONCLUSION

• Effective method to inactivate microrganisms and
  enzymes especially at high temperatures (Tgt 50C)
• Efficiency increases with
• Electric field strength
• Duration
• Reduced microbial load
• Reduced fat and protein
• Number of pulses
• Temperatures
• Some hurdle techniques

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• THANK YOU