Physical methods can assess fish quality deterioration through several parameters: - Refractive index of eye fluid increases as fish spoils due to concentration of fluids, with higher indexes indicating poorer quality. - Texture changes from techniques like shear tests and puncture tests quantify hardness and springiness to track spoilage. - Electrical conductance rises with tissue decay as cell structures are disrupted, measured by devices like the Torrymeter. - Optical tests detect increased turbidity from surface bacteria using techniques like colorimetry with triphenyl tetrazolium dye.

1. Physical methods
for assessment of
fish quality
deterioration
MOKSHA CHIB
13FET1003

2. PARAMETERS
FOR
ASSESSING
FISH QUALITY
Refractive
index of eye
fluid
Texture
changes
Electrical
Conductance
Optical tests
Viscosity
Drip

3. Refractive Index of Eye Fluids
PRINCIPLE
Refractive Index (RI) of the fluid, the vitreous
humour, recovered from the interior of the eye is
measured and related to the storage time of the
fish.
REASON FOR CHANGE IN REFRACTIVE
INDEX
Eye fluid is bright and transparent but its brightness
is lost with time due to drying. Materials transferred
from tissues around the eye circle into the eye fluid
increase the fluid concentration. Thus, the light
refraction property of eye fluid changes.

4. • Change in RI likely due to the leaching of the potassium salts from the cells lining the eye to the
extracellular vitreous humour, as the ion pump system across the cell membrane degrades on the
death of fish
• RI change is not affected by any bacterial growth in the eye
• Studies showed a linear relationship between the refractive index of eye fluid from haddock &
organoleptic score
Removal of eye
from the head by
making a slit in the
posterior portion of
the eyes
The fluids from each
eye are allowed to
drain into a beaker
Fluids are then
centrifuged &
filtered by passing
through glass wool
RI is determined by
Abbé
Refractometer
using two or three
drops of the eye
fluid
PROCEDURE

5. REFRACTIVE INDEX QUALITY OF FISH
1.3347-1.3366 Very good
1.3367-1.3380 Fair to good
1.3381-1.3393 Poor
> 1.3394 Not marketable
Gogoklu and Yerlikaya 2004
Yapar and Yetim 1998

6. Texture changes
• Textural changes can take place in fish due to biochemical, structural and microbiological changes. Cooking
and freezing conditions also affect the texture
• Textural assessment would include quantifying hardness, springiness, cohesiveness and resilience by
either instrumental or sensory means
• The shape of the fish, the complex, non-uniform structure of the fish muscle, and the slippage of the
myotomes upon cooking make many instrumental methods difficult to apply in fish. The texture properties
also varies from location of the fish, thus adding to the difficulty to the measurement
• Traditional Method: Finger Test- Evaluation of firmness by pressing on the skin or fillet of the fish by finger,
and this method depends largely on subjective assessments of expert panel

7. Kramer Shear Cell
• Standard cell contains an upper part with blades that
penetrate a box with slots
• Upon application of force, the food materials undergo
shearing, compression and extrusion
• SAMPLING: Fillets can be flaked by hand once cooked,
mixed thoroughly, and placed as a uniform layer in the cell
before performing the test or evenly to spread a fixed
amount of diced and cooked fish muscle in random fashion
• Parameters usually measured include maximum force at a
given sample weight, slope, energy of the force-deformation
curve

8. Warner- Bratzler Shear Cell
• The Warner-Bratzler shear cell consists of a blade with two cutting edges forming
an angle of 60°, which penetrates another device with a slot.
• The blade cuts the sample like a guillotine and is thus subjected to a complex
combination of tension, compression and shearing
• It is very to take into account how the fibers are oriented with respect to the blade,
and therefore the Warner-Bratzler method is difficult to perform, especially with
small pieces of fish muscle. The blade needs to be sharpened regularly
• The shearing takes place in a very localised area of the muscle, causing distortion
of the muscle fibers
• Can be used for studying the influence of factors such as different cooking
temperature & ice storage on the texture

9. Puncture Test
• Consists of measuring the force required to push a plunger (conical, cylindrical,
wedge-shaped) into a food sample, which is thus subjected to a combination of
compression and shearing in proportion to the area of the cross-section of the
plunger
• The plunger penetrates either to a constant depth or to the point of rupture. The
applied force can increase linearly or at a constant rate
• There is initial rapid increase in the force as the probe moves inside the food. After
the punch begins to penetrate, this leads to a sudden change in slope called Yield
Point, which marks the instant where the punch begins to break the food
• This method has been used to assess the changes occurring in texture during
storage in ice. It can also be used to analyze the texture of fish gels

10. TENSION ANALYSIS
• Measures the force required to break a
sample in two when it is held by two
parallel clamps, one of which moves
away from the other at a constant rate
• The sample is cut into dumb-bell shapes
or strips and the parameters normally
measured are maximum force or tensile
strength and energy
• Sampling must be proper otherwise can
lead to slipping or premature breaking in
the clamps
COMPRESSION TEST
• Performed on application of a uniaxial compression force,
between two parallel flat surfaces, one fixed and the
other moveable
• There is a change in shape during compression but no
change in the volume
• Probe should be larger than the sample
• The deformation rate, the friction at the contact surfaces,
and the physical dimensions of the samples can have a
high influence on the force deformation curves
• Slippage of myotomes in cooked fish samples can occur,
thus it is not considered to be suitable for analysis of
cooked products
• A compression force that exerts 50% deformation is used
for a product of minced and cooked carp however, for fish
mince or fillets 30% and 10% deformation is used

11. Cylinder Probe Texturometer
• Mechanical devices for measuring the texture of fish usually involve some kind of
cylindrical probe that presses into the fish with the force, F, increasing to a preset value.
The corresponding depth, h, of the concavity produced can be measured and related to
the elasticity of the flesh

12. Open Cylinder Probe Texturometer
• It involves a small open-ended cylinder (outer diameter dO , inner diameter dI ) that would cause a
"meniscus" of flesh of height h to swell up across the diameter of the probe. The advantage of this
approach would be that a sensor to measure h could be built inside the probe
Specifications:
dO = 40mm
dI = 30mm
Speed of the cylinder = 30mm/min

13. Hand-held device as initially envisaged, shown testing
a piece of foam rubber
Close-up of the cylindrical tube and the meniscus height
sensor
Compression Test

14. Texture Profile Analysis (TPA)
• Consists of compressing a sample twice in back-and-forth movement, mimicking the action of the jaw
• The force- deformation curve is analyzed to determine a number of texture parameters like maximum
force at 1st & 2nd compression cycles considered as hardness, and ratio of the force areas under the 1st
& 2nd compression considered as cohesiveness
• Other parameters measured are load at maximum displacement, deformability modulus and relaxation
time
• If the test is done in conditions where the sample size is much smaller than the probe, the forces derive
mostly from uniaxial compression. In the opposite case, the forces derive mostly from puncture, that is,
compression and shearing

15. PARAMETE
R
DESCRIPTION
Springiness Range within which a deformed material
recovers its non-deformed shape after the
force is released
Cohesivity Strength of the internal borders which form
the body of the product
Masticability Required energy to masticate a solid amount
of food till it is ready to be swallowed
Gumminess Required energy to disintegrate a semi-solid
food product till it is ready to be swallowed
Adhesiveness Necessary amount of work to counteract the
attraction forces between the surface of the
food and the surface of other materials
Hardness Necessary effort to obtain a given
deformation
Elasticity Property of a material allowing it to recover
its non-deformed shaped after being
compressed

16. Durometer
• Measures hardness of the snow crab
• Has a broad 3.175mm diameter hemispherical indenter
which doesn’t penetrate the shell
• A 2.5 cm stainless steel or aluminum extension rod
separates the indenter from the body of the instrument
• Crab to be classified as hard shelled must have a
reading of 68
Durometer

17. Electrical Conductance
• Disruption of cell structures (containing electrically conducting fluids) with tissue decay causes large
changes in the overall electrical conductivity and in the capacitance due to autolysis
• During storage, several other post mortem changes in the fish muscle affect quality through
mechanisms that could also alter the dielectric properties
• Most changes affect interactions between water and proteins, and degradation processes leading to the
formation of polar compounds

18. Torrymeter
• Measures the effects of spoilage on the electrical
properties of fish tissues by the use of four-electrode
system
• The applied current is through two electrodes at which
polarization develops. Positioned between these
current electrodes, a further pair of electrodes
connected to a very high input impedance, draw no
current and just measure the electric potential
• The potential electrodes are made up of stainless steel
& the concentric current electrodes are of graphite
• The output is read in the form of a digital number from
a scale of 0-18
0-4 : Fish unfit for consumption
14-18 : Very fresh fish

19. Relationship between GR Torrymeter readings of various
species of fish and freshness

20. Intellectron Fischtester VI
• Measures the electrical properties ( conductance, impedance & capacitance) of the fish flesh
• Fischtester can measure the resistance of the cell tissue by dividing it into different components:
resistance of the interstitial liquid, resistance of the cell content, resistance of the cell wall & the capacity
of the cell wall
• It measures transversally through the entire fish; the electrodes are applied on the lateral line of the
body close to the anal opening
• The readings can range from 0-100 Ω
• Suitable for fresh fish grading, for determination of days in ice & prediction of days in ice left for lean fish
species

21. Optical Tests
• Ultraviolet fluorescence and luminescence of dispersions are carried out which report changes in the color
of fluorescence occurring during storage
• Bacterial decomposition on the surface of the fish loaf shows increased turbidity of the surface washings
which cane be measured by turbid metric method
• Optical test for establishing the presence of spoilage in crabmeat is based on turbidity of alcohol extracts that
developed upon the addition of saturated aqueous picric acid solution
• Computer screen photo assisted technique (CSPT) is used to display millions of colors, combining
wavelengths in optical range & also evaluates the absorbance and fluorescence of the samples

22. Detection of spoilage by Colorimetry
Triphenyl Tetrazolium dye
( Colorless, ionized, water soluble
& capable of passing through the
cell wall of bacterial cell)
Triphenyl Tetrazolium formazan
( Red-colored, non ionic, water-
insoluble, deposits within the bacterial
cell)
The intensity of the formed color is proportional to the concentration of bacteria present which is necessary to
provide reduction reaction
Incase of dark-flesh finfish, such as tuna fish, additional oxidizing or bleaching agents like H2O2 are added to
bleach the muscle pigment & lighten the color of the solution so that the only color seen is due to the assay
Colorless solution - Excellent Quality
Light reddish color – Good Quality
Darker red color - Borderline Quality
Intense red color – Unacceptable Quality

23. Viscosity
• Measurement of the apparent viscosity of a fish muscle homogenate has been proposed as an indicator of
quality
• The conditions are optimized for measurement of apparent viscosity of a muscle homogenate in a solution
of 5% NaCl (1:4) and pH 6.5-7.0 as a quality control measure
• Viscosity of an actomyosin dispersion can determine the apparent viscosity
• Viscosity is expected to decrease on frozen storage and it depends upon the species of the fish
• It has also been found to depend upon the storage temperature & the season

24. Drip Measurement
• Drip loss measurement includes subjecting the fish samples to High Pressure Thawing (HPT)
which will lead to reduction in the drip loss. Slower the freezing, larger are the ice crystals resulting
in more tissue damage & thawing loss
PROCEDURE
Batches of the
packed samples
are subjected to
freezing
Samples are
thawed by HPT
with the temp of the
pressure medium to
be 20°C
Fish sample is
removed from the
pouch, leaving
behind the drip
Drip loss is
computed from the
weight of the drip &
the sample
Freezing processes: Conventional air freezing (CAF), Plate freezing (PF), Liquid Nitrogen Freezing
(LNF)