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FOSC302 > High Pressure > Flashcards

High Pressure Flashcards

1
Q

type of processing for:
solid foods
liquids

A

solid: batch
liquid: semi continous

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2
Q

machinery required

A

pressure vessel and pressure generator

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3
Q

describe process

A

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

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4
Q

why is water important

A

it is virtually incompressible

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5
Q

describe process

A

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

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6
Q

what is the isostatic principle

A

pressure is transmitted instantaneously and uniformly throughout the sample
-independent of volume and geometry of the sample

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7
Q

describe process

A

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

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8
Q

describe process

A

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

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9
Q

what is the isostatic principle?

A

pressure is transmitted instantaneously and uniformly throughout the sample
-independent of the volume and geometry of the sample

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10
Q

why is LeChateliars principle important

A

reactions that result in a volume decrease are stimulated
-those causing a volume increase are disrupted

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11
Q

what happens if bacteria tries to grow under pressure

A

bursts as system tried to reestablish equilibrium

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12
Q

what happens to inoic bonds

A

broken

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13
Q

what type of bonds are favoured

A

hydrogen

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14
Q

what type of bonds are unaffected

A

covalent

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15
Q

examples of covalent bonds in food

A

low molecular weight, resonsible for sensory nad nuutritional qualitity

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16
Q

does the maillard reaction occur

A

no

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17
Q

examples of changes in high molecular weight molecules

A

protein, starches have altered functionality

18
Q

where is the primary site of damage in cells

A

cell membrane
-disruption in function and leakage

19
Q

what happens to the cell membrane

A

volume and cross-sectional area of bi-layer is reduced

20
Q

what can happen to enzymes

A

change on active site conformation
alteration of intramoleuclar structure

21
Q

steps of DNA replication that are disrupted by pressure

A

replication and transcription

22
Q

are eukaryotes or prokaryotes more resistant

A

eukaryotes

23
Q

which is the most resistant stage of growth

A

stationary more than exponential

24
Q

what substrates confer protection

A

proteins, lipids and carbs

25
Q

what does a rich media supply

A

more amino acids for stressed cells

26
Q

why does pH of aqueous solutions decrease with pressure

A

electrostriction

27
Q

what temperature should be treated at

A

below ambient (2 or 10 C)

28
Q

how does applying mild heat affect the inactivation of resistant vegetative pathogens

A

more effective
-E.coli
-S.aureus

29
Q

two mechanisms for steralisation using pressure

A
  1. lower pressure and temps causes spores to germinate and they are then inactivated by pressure
  2. at higher temps a direct spore-inactivation mechanism occurs
30
Q

why are inactivation curves observed under higher temperatures for sterilisation harder to interpret

A

they dont follow first-order kinetics

31
Q

how does high pressure affect proteins

A

reversible or irreversible denaturation

32
Q

what does the denaturation of proteins depend on

A

kind of protein
processing conditions
pressure applied

33
Q

above what pressure does dentauration of proteins and inactivatoin of enzymes occur

A

300Mpa

34
Q

at pressure <300MPa what happens to enzyme activity

A

accelerated

35
Q

how are proteins denatured

A

destruction of hydrophobic and ion-pair bonds and unfolding of molecules

36
Q

what is HP used for in japan

A

surimi

37
Q

what happens to starch under HP

A

they can become gelatinised

38
Q

what pressure gelatinizes starch

A

400-500MPa
40-50C

39
Q

how are enzyme affected by HP

A

heat treatment is more affective for inactivation but used in combination with HP there may be inactivation

40
Q

commercial application of HP

A

mandarin juice: inibited mould
grapefruit juice: inhibited bitter taste
Oysters: pressure 200-300MPa 5-15 mins, 25C inactivated vibrio bacteria

41
Q

cost of HP

A

high capital cost ~10 mill
production costs ~ 4.5 c per kg/l

42
Q

advantages

A

-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

FOSC302 (14 decks)

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