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Results and achievements
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Reduction
of L. monocytogenes
in heat sensitive products
like egg based products
by at least 4 log CFU/ml is possible by combining PEF
treatment with mild heat treatment (55ºC) or by performing PEF
treatments in series with chilling between treatment in order
to limit the temperature increase in the product.
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Using PEF treatment
and
potassium sorbate gives an
additive effect on the time for L. monocytogenes
to grow to unacceptable numbers during storage.
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Treatments with
combinations of electric field levels up to 40kV, a pulse
width up to 10 µs and up to 125 pulses were applied on
bacteria in phosphate buffer, where the resulting energy input
led to a maximum temperature increase of 45ºC.
The reduction of L. monocytogenes during these PEF treatments of
low acid food was maximum 2.8 log CFU/ml.
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A satisfying
reduction of L. monocytogenes and Salmonella was obtained by
repeated treatment of PEF,
using treatment equipment that cools down the product between
each PEF cycle. The total energy input was increased by
increasing the number of pulses.
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Proteolytic activity
was not detected in PEF treated samples. Only a
slight hydrolytic activity of the lipid fraction was observed
after one week at 4ºC, when they were previously homogenised.
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Microstructural results
showed a highly affected lipoprotein
matrix in whole liquid egg treated by PEF. The
continuity of the protein network was broken and some protein
granules from the yolk were degraded, especially when high
field strength was applied.
However, in pasteurised samples a reinforcement of
protein-protein interactions was observed. The whole egg
homogenisation produced a protein granules aggregation and the
protein-protein interactions in the lipoprotein matrix were
reinforced.
