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FOSC202 > Fish Quality > Flashcards

Fish Quality Flashcards

1
Q

sensory, microbial, and chemical quality indices

A

odour
appearance
texture
flavour

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2
Q

how many phases of deterioration are there for fish

A

4

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3
Q

describe phase 1

A

fresh
characteristic odour
delicate taste

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4
Q

how long does phase 1 last

A

almost 2 days

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5
Q

describe phase 2

A

loss of odour and taste
autolysis begins

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6
Q

what is autolysis

A

biochemical changes and degradation of proteins, nucleotides and molecules

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7
Q

days of phase 2

A

2-6

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8
Q

describe phase 3

A

‘fishy’ odour associated with
microbial spoilage
enzymatic reactions

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9
Q

days that phase 3 occur

A

6-12

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10
Q

describe phase 4

A

putrid odour, mushy/soft texture
advanced proteolysis

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11
Q

days that phase 4 occurs

A

> 12 days

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12
Q

what are cephalopods

A

squids etc

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13
Q

how does glycolysis occur in fish

A

-6C and 3C molecules are transformed to pyruvate
-pyruvate is used in TCA cycle and converted to lactate (except cephalopods)

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14
Q

what is pyruvate converted to in cephalopods

A

octopine

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15
Q

consequences of octopine conversion over lactate

A

results in a higher ultimate pH

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16
Q

why is the pH drop in fish less than terrestrial animals

A

less glycogen stored

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17
Q

typical pH fall in fish

A

6.8-7.2 intially
drops to 6.1-6.9

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18
Q

% of glycogen stores in land animals vs fish

A

2-1% in land
0.5% in fish

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19
Q

when does rigor develop in fish

A

2 hrs after death

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20
Q

when does rigor resolve in fish

A

1 day

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21
Q

what is the rate of onset of rigor determined by

A

temperature (cold or tropical fish)
condition
handling
size

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22
Q

is rigor desired in
-fish
-red meat

A

yes in fish
no in reed meat

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23
Q

why is rigor wanted to be preserved in fish

A

the firmness of fish makes it more difficult for bacteria to move to the surface

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24
Q

what ‘condition’ could result in low glycogen stores in fish

A

spawning

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25
Q

types of physical and biochemical changes associated with the rate of rigor that affects the quality

A

gapping
proteolysis

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26
Q

what is gapping caused by

A

rapid onset of rigor

27
Q

when does gapping occur

A

when cold water fish are stored at too high of a temp it can cause rapid onset of rigor

28
Q

what happens during gapping

A

strong contraction cause weakening of CT (mycommata) which ruptures the fillet resulting in the segementation of myotomes

29
Q

what does proteolysis of hoki cause

A

softening

30
Q

which protease is calcium dependant and involved in Hoki softening

A

calpains

31
Q

how can the deterioration of Hoki be slowed

A

rapid chilling from 12-1 degrees

32
Q

what is nucleotide degradation

A

degradation of ATP to biochemical compounds that affect sensory attributes

33
Q

reaction scheme of ATP degradation

A

ATP-> ADP->AMP->IMP->inosine->hypoxanthine

34
Q

how does AMP-> IMP

A

deamination

35
Q

which product is desirable in nucleotide degradation

A

inosine monophosphate (IMP)

36
Q

what flavor does hypoxanthine produce

A

bitter

37
Q

difference betwen inosine andIMP

A

not much but IMP is better

38
Q

how is inosine broken down

A

phosphotase enzyme

39
Q

what is a K factor

A

freshness index/spoilage indicator

40
Q

what are the components of K factor equation

A

ino and Hx/ total ATP related products

41
Q

what does a high K factor indicate

A

less fresh

42
Q

5 autolytic changes in fish

A

glycolysis
nucleotide breakdown
proteolysis
lipolysis//autooxidation
TMAO breakdown

43
Q

enzymes and substrate of glycolysis

A

glycolytic enzymes
glycogen

44
Q

enzymes and substrate of nucleotide breakdown

A

endogenous autolytic enzymes
ATP, ADP, AMP, IMP,

45
Q

enzymes and substrate of proteolysis

A

calpains and cathepsins
proteins, peptides myofribrills, CT

46
Q

enzymes and substrate of lipolysis

A

lipases and phospholipases
lipid and phospholipids

47
Q

enzymes and substrate of autoxidation

A

lipoxygenases
PUFAs

48
Q

enzymes and substrate of TMAO breakdown

A

TMAO demethylase
TMOA

49
Q

how to prevent/ inhibit glycolysis causes defective changes

A

allow the fish to pass through rigor at temps close to 0

50
Q

how to prevent/ inhibit nucleotide breakdown

A

low temp
careful handling

51
Q

how to prevent/ inhibit proteolysis

A

careful handling
low temp

52
Q

what is TMAO

A

a substance present naturally
stablises intracellular proteins and denaturation of urea

53
Q

process of TMAO breakdown

A

reduced by bacteria to TMA and
enzymatically converted to DMA and formaldehyde

54
Q

changes encountered by TMAO breakdown

A

toughening

55
Q

what does TMA cause

A

fishy off flavour

56
Q

what does formaldehyde do

A

induces protein cross-linking

57
Q

shelf life of frozen fish

A

3 months

58
Q

what does longer freezer storage of protein cause

A

less extractable protein

59
Q

impact of freezing on fish

A

protein denaturation and texture deterioration

60
Q

what do proteins interact with during degradation

A

water, lipids and endogenous enzymes

61
Q

examples of texture deterioration from freezing

A

toughening
drying/ loss of succulence

62
Q

examples of flavour deterioration from freezing

A

development of off-flavours from
-lipid hydrolysis and oxidation
-formation TMA

63
Q

examples of loss of protein functional properties from freezing

A

loss in WHC, solubility, gelling capability, lipid emulsifying capability

FOSC202 (28 decks)

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