47
OCT 2017 FOOD FOCUSTHAILAND
SMART
PRODUCTION
HowdoesHPPaffectGermsbutnot
Nutrients?
Since high pressures have limited effects on
covalent bonds within low molecular-mass
compounds such as colours, flavours, and
odours, HPP does not affect fresh-like
characteristicsof treatedsamples. Inaddition,
moderate HPP at 400-600 MPa at ambient
temperature also does not have impacts on
the total antioxidant activityof foodcontaining
ascorbic acid, anthocyanin, and phenolic
molecules. Whereas biomembranes of
pathogens and spoilage microbes, which
comprise a bilayer of phospholipids with
embedded functionalproteins,undergophase
transitionsunderpressure,causingadecrease
in biomembrane fluidity, and subsequently,
leading to breakage of the membrane and
denaturationof themembrane-boundproteins.
Theseproteins thusmalfunction in transporting
substancesacross themembranes,giving rise
to leakage of intracellular metabolites and
permeation of extracellular substances into
cells and tissues, hence, cell death.
Generally, commercial HPP at 400-700
MPa conducted at room temperature can
potentially inactivate most micro-organisms
and enzymes. Nonetheless, to achieve
complete inactivation, the process also
dependsonother factors, for instance, typeof
pressure treatment (cyclic or continuous),
operation time,speciesandstrainofmicrobes
(Gram type), growth stage and age of the
culture, and composition and properties of
transmitting medium (ionic strength, water
activity, pH, etc.). Moreover, spore-forming
bacteria tolerate pressure below 1,200 MPa
atambient temperature,or termperaturebelow
90
o
Cat 500-700MPa.
TheHPP treatment canalsobecombined
withothernon-thermal techniques toboost the
efficiency indeactivationofmicro-organisms,
for instance, HPP at 400 MPa for 5 or 30
minutes together with gamma irradiation can
inactivate bacteria and yeast in kefir without
altering its proteins and lipids. Alternatively,
application of HPP can reduce the gamma-
radiation dose required to deactivate
Clostridium sporogenes
spores and extend
the shelf life of chickenmeat. A combination
of an alternating current (50 Hz) and HPP at
300MPa for 10minutes and at 400MPa for
30 minutes can enhance lethal damage on
Escherichia coli
cells and
Bacillus subtilis
spores, respectively.
Rhodotorula rubra
is an
exampleofmicrobes that are tolerant toHPP,
nevertheless, ultrasound treatment followedbyHPPat 400MPa for 25minutescan lead
to complete inactivation at 15
o
C.
Bacillus cereus
spores inwater containing argon can
be inactivated by HPP at 600 MPa at 20
o
C. Carbon dioxide can effectively reduce
germination when integrated with HPP. Aerobes in carrot juice can be completely
destructedby thecombined treatmentof carbondioxide (4.90MPa)andHPP (300MPa).
CarbondioxideandHPPcanalsoeffectivelydecrease theactivityofpectinmethylesterase,
polyphenol oxidase,
Lactobacillus plantarum
, and
Escherichia coli
.
HPP Industrial Procedures
Industrial HPP can be catergorised into three types, namely, batch system, continuous
system,andsemi-continuoussystem.Thebatchsystemcanprocessboth liquidproducts
