Fish Quality Flashcards
sensory, microbial, and chemical quality indices
odour
appearance
texture
flavour
how many phases of deterioration are there for fish
4
describe phase 1
fresh
characteristic odour
delicate taste
how long does phase 1 last
almost 2 days
describe phase 2
loss of odour and taste
autolysis begins
what is autolysis
biochemical changes and degradation of proteins, nucleotides and molecules
days of phase 2
2-6
describe phase 3
‘fishy’ odour associated with
microbial spoilage
enzymatic reactions
days that phase 3 occur
6-12
describe phase 4
putrid odour, mushy/soft texture
advanced proteolysis
days that phase 4 occurs
> 12 days
what are cephalopods
squids etc
how does glycolysis occur in fish
-6C and 3C molecules are transformed to pyruvate
-pyruvate is used in TCA cycle and converted to lactate (except cephalopods)
what is pyruvate converted to in cephalopods
octopine
consequences of octopine conversion over lactate
results in a higher ultimate pH
why is the pH drop in fish less than terrestrial animals
less glycogen stored
typical pH fall in fish
6.8-7.2 intially
drops to 6.1-6.9
% of glycogen stores in land animals vs fish
2-1% in land
0.5% in fish
when does rigor develop in fish
2 hrs after death
when does rigor resolve in fish
1 day
what is the rate of onset of rigor determined by
temperature (cold or tropical fish)
condition
handling
size
is rigor desired in
-fish
-red meat
yes in fish
no in reed meat
why is rigor wanted to be preserved in fish
the firmness of fish makes it more difficult for bacteria to move to the surface
what ‘condition’ could result in low glycogen stores in fish
spawning
types of physical and biochemical changes associated with the rate of rigor that affects the quality
gapping
proteolysis
what is gapping caused by
rapid onset of rigor
when does gapping occur
when cold water fish are stored at too high of a temp it can cause rapid onset of rigor
what happens during gapping
strong contraction cause weakening of CT (mycommata) which ruptures the fillet resulting in the segementation of myotomes
what does proteolysis of hoki cause
softening
which protease is calcium dependant and involved in Hoki softening
calpains
how can the deterioration of Hoki be slowed
rapid chilling from 12-1 degrees
what is nucleotide degradation
degradation of ATP to biochemical compounds that affect sensory attributes
reaction scheme of ATP degradation
ATP-> ADP->AMP->IMP->inosine->hypoxanthine
how does AMP-> IMP
deamination
which product is desirable in nucleotide degradation
inosine monophosphate (IMP)
what flavor does hypoxanthine produce
bitter
difference betwen inosine andIMP
not much but IMP is better
how is inosine broken down
phosphotase enzyme
what is a K factor
freshness index/spoilage indicator
what are the components of K factor equation
ino and Hx/ total ATP related products
what does a high K factor indicate
less fresh
5 autolytic changes in fish
glycolysis
nucleotide breakdown
proteolysis
lipolysis//autooxidation
TMAO breakdown
enzymes and substrate of glycolysis
glycolytic enzymes
glycogen
enzymes and substrate of nucleotide breakdown
endogenous autolytic enzymes
ATP, ADP, AMP, IMP,
enzymes and substrate of proteolysis
calpains and cathepsins
proteins, peptides myofribrills, CT
enzymes and substrate of lipolysis
lipases and phospholipases
lipid and phospholipids
enzymes and substrate of autoxidation
lipoxygenases
PUFAs
enzymes and substrate of TMAO breakdown
TMAO demethylase
TMOA
how to prevent/ inhibit glycolysis causes defective changes
allow the fish to pass through rigor at temps close to 0
how to prevent/ inhibit nucleotide breakdown
low temp
careful handling
how to prevent/ inhibit proteolysis
careful handling
low temp
what is TMAO
a substance present naturally
stablises intracellular proteins and denaturation of urea
process of TMAO breakdown
reduced by bacteria to TMA and
enzymatically converted to DMA and formaldehyde
changes encountered by TMAO breakdown
toughening
what does TMA cause
fishy off flavour
what does formaldehyde do
induces protein cross-linking
shelf life of frozen fish
3 months
what does longer freezer storage of protein cause
less extractable protein
impact of freezing on fish
protein denaturation and texture deterioration
what do proteins interact with during degradation
water, lipids and endogenous enzymes
examples of texture deterioration from freezing
toughening
drying/ loss of succulence
examples of flavour deterioration from freezing
development of off-flavours from
-lipid hydrolysis and oxidation
-formation TMA
examples of loss of protein functional properties from freezing
loss in WHC, solubility, gelling capability, lipid emulsifying capability
