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Bangabandhu Sheikh Mujibur Rahman Agricultural

University

Salna, Gazipur-1706

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Fresh fish is a highly perishable product.

Loss of quality depends on: Nature of fish species and on the handling

and storage

Rainbow trout (O. mykiss) is a fatty fish species deterioted by

microorganisms and lipid oxidation.

Lipid oxidation cause rancidity problem.

Which leads to off-flavor and off-odor.

Quality assessment of farmed rainbow trout . . .

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Figure 01:Flow chart of sample preparation Steps.

Quality assessment of farmed rainbow trout . . .

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Sample Taken From the Flesh Of The

Anterior Dorsal Region (40 gm)

Homogenizing

Blending for 60sec

Without skin

or bones

Figure 02: Preparation of sample for Chemical Analysis.

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These homogenized sample were used for the determination of the following chemical

parameters:

Content Method Expressed as

TVB-N content Goudlas and Kontaminas (2005) mg TVB-N per 100 g

Free fatty acid (FFA) Egan and others (1997) percent of oleic acid

Peroxide value (PV) Egan and others (1997) meq of peroxide oxygen/kg fat

Thiobarbituric acid (TBA) Kirk and Sawyer (1991) mg malondialdehyd/ kg fish

flesh

heme iron content Clark and others (1997) mg/100 g

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Table 1 : Descriptive sensory evaluation definitions and descriptors.

Texture General appearance Gill odor Gill appearance Eyes Score

Flesh is firm and

resilient and

springs back

immediately

when released

Good overall

appearance, skin

lustrous and shiny, no

fading

Characteristic of

species, fresh

Bright red, little mucus Clear, bright

convex

eyes

0

Reasonably firm,

some loss of

resiliency, thumb

indentation slowly

fills out

Good overall

appearance, very

slight bleaching of

skin

Neutral. Total absence

of odor, characteristic

odor no longer

detectable but off-

odors have not

developed

Red, some mucus Slightly sunken or

somewhat dull

1

Moderately firm,

thumb indentations

may remain in flesh

Some loss of metallic

luster, some bleaching

Slight to moderate

sour odor

Pinkish red to brownish,

some mucus

Dull and/or cloudy 2

Excessively soft

flesh

Bloom gone from

skin, color faded and

bleached

Very sour, strong, or

putrid

Brown, may be covered

with mucus

Very dull, sunken,

and

cloudy

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0 = Excellent;

1 = Good;

2 = Acceptable;

>2 = Reject.

Parameter

Quality assessment of farmed rainbow trout . . .

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Figure 2: Steps of microbiological analysis.

Quality assessment of farmed rainbow trout . . .

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Table 2: Changes in the total volatile basic nitrogen (TVB-N), free fatty acids (FFA), peroxide value

(PV), and thiobarbituric acid (TBA) value in rainbow trout over the period of storage.

Days in ice TVB-N (mg N/100g) FFA (% of oleic

acid)

PV (meq/kg) TBA (mg MA/kg)

0 22.40 ± 1.57a 1.50 ± 0.37a 1.17 ± 0.47a 0.050 ± 0.01bc

4 29.86 ± 2.77b 1.81 ± 0.27ab 4.25 ± 1.03bc 0.027 ± 0.00a

8 28 ± 0.87ab 2.13 ± 0.39b 6.25 ± 2.95c 0.032 ± 0.00a

12 25.9 ± 2.56ab 2.20 ± 0.22b 4.26 ± 1.25bc 0.028 ± 0.00a

16 24.5 ± 0.9ab 2.30 ± 0.10b 1.28 ± 0.25a 0.042 ± 0.00ab

20 28.23 ± 1.45ab 2.89 ± 0.38c 3.48 ± 1.73abc 0.060 ± 0.00c

Quality assessment of farmed rainbow trout . . .

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Fatty acids may be converted to odorous volatiles.

Occurred during the storage of rainbow trout in ice

FFA content increased with time

A relationship between FFA release and loss of freshness .

Quality assessment of farmed rainbow trout . . .

12Figure 3: Changes in heme iron content of rainbow trout samples stored in ice.

Each value represents the mean of 3 samples ± standard deviation.

Quality assessment of farmed rainbow trout . . .

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Quality assessment of farmed rainbow trout . . .

Figure 4: Changes in the Total Viable Count (TVC) of rainbow trout samples stored in ice.

Each value represents the mean of 3 samples ± standard deviation.

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Quality assessment of farmed rainbow trout . . .

Scoring was 0 = excellent; 1 = good; 2 = acceptable; > 2 = reject. Each value represents the mean of 3

samples.

Attribute Days of storage

0 4 8 12 16 20

Texture 0 0 1 1.67 2.67 3

General appearance 0 0 0.67 1.33 2.33 3

Gill appearance 0 0.33 1.33 2 2.67 3

Gill odor 0 0.67 1.67 2.33 3 3

Eye color 0 0.33 1.33 2 2.67 3

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Quality assessment of farmed rainbow trout . . .

Rainbow trout shelf life in ice was approximately 9 to 11 d.

After that time of storage, the fish had developed spoilage

characteristics.

Continuously leading to a reduction in the shelf life of fish in ice.

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