High Pressure Flashcards
type of processing for:
solid foods
liquids
solid: batch
liquid: semi continous
machinery required
pressure vessel and pressure generator
describe process
packaged food is loaded in and the container is sealed, transmission fluid is pumped in until pressure is reached, valves are then shut for the desired time period
why is water important
it is virtually incompressible
describe process
packaged food is loaded in and the container is sealed, transmission fluid is pumped in until pressure is reached, and valves are then shut for desired time period
what is the isostatic principle
pressure is transmitted instantaneously and uniformly throughout the sample
-independent of volume and geometry of the sample
describe process
packaged food is loaded in and the container is sealed, transmission fluid is pumped in until pressure is reached, and valves are then shut for the desired time period
describe process
packaged food is loaded in and the container is sealed, transmission fluid is pumped in until pressure is reached, and valves are then shut for the desired time period
what is the isostatic principle?
pressure is transmitted instantaneously and uniformly throughout the sample
-independent of the volume and geometry of the sample
why is LeChateliars principle important
reactions that result in a volume decrease are stimulated
-those causing a volume increase are disrupted
what happens if bacteria tries to grow under pressure
bursts as system tried to reestablish equilibrium
what happens to inoic bonds
broken
what type of bonds are favoured
hydrogen
what type of bonds are unaffected
covalent
examples of covalent bonds in food
low molecular weight, resonsible for sensory nad nuutritional qualitity
does the maillard reaction occur
no
examples of changes in high molecular weight molecules
protein, starches have altered functionality
where is the primary site of damage in cells
cell membrane
-disruption in function and leakage
what happens to the cell membrane
volume and cross-sectional area of bi-layer is reduced
what can happen to enzymes
change on active site conformation
alteration of intramoleuclar structure
steps of DNA replication that are disrupted by pressure
replication and transcription
are eukaryotes or prokaryotes more resistant
eukaryotes
which is the most resistant stage of growth
stationary more than exponential
what substrates confer protection
proteins, lipids and carbs
what does a rich media supply
more amino acids for stressed cells
why does pH of aqueous solutions decrease with pressure
electrostriction
what temperature should be treated at
below ambient (2 or 10 C)
how does applying mild heat affect the inactivation of resistant vegetative pathogens
more effective
-E.coli
-S.aureus
two mechanisms for steralisation using pressure
- lower pressure and temps causes spores to germinate and they are then inactivated by pressure
- at higher temps a direct spore-inactivation mechanism occurs
why are inactivation curves observed under higher temperatures for sterilisation harder to interpret
they dont follow first-order kinetics
how does high pressure affect proteins
reversible or irreversible denaturation
what does the denaturation of proteins depend on
kind of protein
processing conditions
pressure applied
above what pressure does dentauration of proteins and inactivatoin of enzymes occur
300Mpa
at pressure <300MPa what happens to enzyme activity
accelerated
how are proteins denatured
destruction of hydrophobic and ion-pair bonds and unfolding of molecules
what is HP used for in japan
surimi
what happens to starch under HP
they can become gelatinised
what pressure gelatinizes starch
400-500MPa
40-50C
how are enzyme affected by HP
heat treatment is more affective for inactivation but used in combination with HP there may be inactivation
commercial application of HP
mandarin juice: inibited mould
grapefruit juice: inhibited bitter taste
Oysters: pressure 200-300MPa 5-15 mins, 25C inactivated vibrio bacteria
cost of HP
high capital cost ~10 mill
production costs ~ 4.5 c per kg/l
advantages
-instant and uniform treatment independent of size and geometry
-once pressure is reach it does not require energy to hold it
-environmentally friendly
-minimal adverse effect/product stays fresh
-low running cost
-considered as natural process
