RAINBOW TROUT [SALMO IRIDEUS) PRODUCED IN
FINLAND

VII. CHANGES IN THE ORGANOLEPTIC QUALITY AND PETTY ACID
COMPOSITION DURING FROZEN STORAGE

Elina Varesmaa, Jorma J. Laine and F. P. Niinivaara

University of Helsinki, Institute of Meat Technology

Received May 13, 1969

Until now freezing has been one of the most important means of storing fish. Several
investigators have tried to solve the problems connected with the changes in the fish
protein during frozen storage (Cowie et al. 1966 and 1967, Olley et al. 1967).

Changes in the lipid fraction of the fish may be of equal importance in lowering the
quality of the fish, especially fatty fish, during frozen storage. The purpose of this study
was to examine the effect of two different storage temperatures and two different means
of packaging upon the organoleptic quality and the fatty acid composition of frozen rain-
bow trout.

Material and methods
The experiments were carried out with second-summer rainbow trout fed with Clark

dry food for rainbow trout. The average weight of the fishes was 130 grams (from 85 to
201 grams) and the control fishes were transported to the laboratory alive. The rest of the
fishes were killed and gutted and frozen rapidly at —40° C. One half of the fishes were
glazed with water while the second half was individually packed in vacuum sealed poly-
ethylene bags. The fishes were then transported to the laboratory in styrox containers
into which CO a-ice had been added. The fish arrived at the laboratory 18 hours after
gutting. At the laboratory the samples were divided again into two halves with storage
temperatures of 18 and 32° C. For the organoleptic evaluation samples were taken
from the control fish after 1 day, 1 week, 1 month and 3 months, and for the fatty acid
analyses from the control fish after 1 day, 1 week, 1 month and 7 months.

The organoleptic evaluation was performed according to Niinivaara et ai. 1966, and
the fatty acid analyses in accordance with the methods used in the previous study (Vares-
maa et al. 1968).



161

Results
Organoleptic evaluation. The results obtained in the organoleptic

evaluation are presented in Table 1. They indicate that already after three months of
storage the fish was uneatable. At 32 ° C the fish kept their organoleptic quality some-
what better than at 18° C. No marked differences existed between the glazed and the
vacuum-packed fish.

Fatty acid composition of lipids. The results from the fatty acid
analyses are presented in Table 2. No marked differences during the storage, nor any
correlations between the types ofpacking and storage temperatures, could be noticed.

Discussion
According to the results obtained in this examination, the possibilities of applying

freezing in the storage of rainbow trout are limited. In organoleptic evaluation the fishes
were judged uneatable after three months of storage. In this respect the results are differ-
ent from results obtained by other investigators. Bramsnaes et al. (1960) found that rain-
bow trout began to go rancid only after 9 months. Nelson (1959) indicated that trout
glazed with water kept their quality for 18 months at 18° C but unglazed trout became
rancid and uneatable in 4 months. On the other hand it is obvious that the keeping quality
of rainbow trout during frozen storage depends upon many factors such as the age of the
fish, the condition of the fish before killing, the catching time, the freezing temperature
and the method of handling before freezing. Many investigations have proved that these
factors affect the quality of the fish and the extent of the storage time (Banks 1952, Nelson
1959, Piskarev 1959, Bramsnaes et al. 1960. Anderson et al. 1961, Lane 1964, Lilje-
mark 1964).

There were no marked differences in the total fatty acid composition of lipids during
storage, nor any greater differences between the storage temperatures and packing types
used. Obviously the reason for the short shelf life does not lie in the fatty acids alone. Ac-
cording to earlier investigations, the free fatty acids formed when the lipids are hydro-
lyzed may, however, react with proteins and cause primary changes in the structure
(Frazer et al. 1959, Ackman 1967). It is therefore probable that changes in the proteins
during frozen storage are more significant than in the lipids causing a rapid lowering in
the quality of frozen rainbow trout.

Summary
Rainbow trouts were frozen at 40° C and stored either glazed with water or vacuum

packed in polyethylene bags at 18°and—32° C. During the storage time the quality of
the fish was tested both organoleptically and by determining the fatty acid composition
of the lipids.

It was found that the fish were organoleptically uneatable after three months ofstorage.
At 32° C the fish kept their organoleptic quality somewhat better than at 18° C.
There were no important differences between the two packing systems used.

The fatty acid analyses gave comparable results in all instances and probably changes
in the proteins during frozen storage are more significant than changes in the lipids and
are mostly responsible for the lowering in quality of frozen rainbow trout.



162

Table 1. Organoleptic quality of gutted trout during storage.

Date Appear- Structure Colour Odour Flavour Total
ance score

Control: fresh 4 3.5 3 + 2 5 18
June 1, 67:
Frozen, glazed 3+ 3 2-j- 2 4 + 15
frozen, vacuum-packed 3.5 3 3 2 5 14 +

June 8, 67:
18° C, vacuum-packed 3 + 3 2.5 2 3.5 14
18° C, glazed 4 3 + 3 2 3.5 15 -f
32° C, vacuum-packed 3 + 3 2 2 3 -j- 13 +
32° C, glazed 3.5 3 + 3 2 4 15 +

July 1, 67:
18° C, vacuum-packed 3 3 3 2 3 14
18° C, glazed 3 + 3 2.5 2 3.5 14 +
32° C, vacuum-packed 2.5 2 + 3 2 3 12,5
32° C, glazed 3.5 3 3 2 4 13 +

Sept. 1, 67:
18° C, vacuum-packed 2 + 3 2.5 1.5 2 + 11 +
18° C, glazed 2+ 3 2.5 1 1.5 10
32° C, vacuum-packed 2.5 2 + 2.5 1.5 2 11
32° C, glazed 2.5 2 + 2.5 1 + 3 11 +

REFERENCES

Agkman, R. G. 1967. The influence of lipids on fish quality. J. Food Tech. 2: 169—181.
Anderson, K. and Danielson, C. E. 1961. Storage changes in frozen fish. A comparison of objekti ve and

subjective tests. Food Tech. 15: 55—57.
Banks, A. 1952. The freezing and cold storage of herrings. Gt. Brit. Dept. Sci. Ind. Research, Food Invest.

Spec. Rept. 55, 40 pp. Ref. Fish as Food 4; 371, 1961 New York.
Bramsnaes, F., Brennum, H. and Sorensen, H. C. 1960. Antioxidant treatment of rainbow trout. Proc.

10 th. Internal. Congr. Refrig. 3: 247. New York.
Cowie, W. P. and Little, W. F, 1966. The relationship between the toughness of cod stored at 29° C

and its muscle protein solubility and pH. J. Food Tech. 1: 335—343.
Cowie, W. P. and Little, W. F. 1967. The relations between the toughness of cod stored at 7° C

and 14° C, its muscle protein solubility and muscle pH. Ibid 2: 217 —222.
Frazer, D. J. and Dyer, W. J. 1959. Fat hydrolysis in frozen fish 11. Progr. Rep. Atlantic Coast Sta.,

Can. (Sept. 1959) N:o 72, pp 37—39, 1 fig. Ref. Bull. Inst. Intern. Ref. N:o 5, 1960, p 1272.
Lane, P. J. 1964. The Time-temperature tolerance of frozen seafoods. I. A review of some of the recent

litterature on the storage life of frozen fishery products. Food Tech. 18: 1100—-1106.
Liljemark, A. 1964. Cold storage of retail-packed fillets of mackerel and herring. Food Tech. 18: 380—

382.
Nelson, R. W. 1959. Keeping rainbows in cold storage. U.S. Trout News. Nov. Dec. Ref. Bull. Inst.

Intern, du Froid. N:o 5, p. 1278.
Niinivaara, F. P., Sihvola, Ritva-Liisa and Laine, J. J. 1966. Rainbow trout (Salmo irideus) produced

in Finland. 1. Bacterial spoilage and amino acid composition of fresh rainbow trout during refrig-
erated storage. J. Sci. Agric. Soc. Finland 38: 210 —220.

Olley, J., Stephen, E., Farmer, J. and Robertson, I. 1967. A critical look at two objective tests for
cold storage deterioration. J. Food Tech. 2: 207—216.



Table
2.

Fatty
acid
composition
of
gutted
trout

during
storage.

1
)

Fresh
June

Ist,
67

June
Bth,
67

J
u
ly

Ist,
67

February
7th,
68

vac.
glaz.

vac
18

glaz
18
vac

32

glaz
32

vac
18

glaz
18
vac

32
glaz

32
vac
18

glaz
18
vac

32

glaz
32

%

%

%

%

%

%

%

%

%

%

•

%

%

%

%

%

C14:0
1.5

1.5

1.5

2.6

2.1

1.4

1.8

2.6

1.7

1.3

1.8

2.7

2.7

2.7

2.8

C15:0
0.6

0.7

1.1

1.7

0.5

0.9

0.5

1.9

0.7

0.4

0.7

0.4

0.7

0.6

0.5

C16:0
16.8
14.2
11.0
14.4
15.7
15.0
15.1

12.9

7.8

8.5

12.6

15.7

14.5
14.9

13.1

C16:l
4.2

3.8

2.9

3.6

5.3

3.8

4.5

3.3

3.1

4.0

3.3

4.4

4.7

4.4

4.2

C17:0
0.9

1.1

1.3

2.8

0.9

1.4

0.8

3.1

0.9

0.7

0.9

0.9

0.9

0.9

0.9

G17;l

0.6

0.8

1.2

0.6

1.0

0.6

2.2

2.1

1.0

0.5

0.8

0.8

0.7

0.5

C18:0
6.7

6.2

8.5

6.9

6.3

5.0

6.1

9.6

4.6

4.2

5.6

24.7
25.3
23.1

22.07

CI8;
1

23.6
22.1
19.4
19.6

19.2
22.9
20.1

15.8
13.7

15.6
17.8

C18:2
11.5
11.0

8.5

18.5
14.7
12.4
14.3

8.3

11.3
10.3
11.8
14.9
16.7

15.1

15.7

C18:3
0.5

1.3

1.4

0.4

0.7

1.4

0.7

2.0

1.5

2.4

2.0

2.4

1.3

2.4

G18:4
1.1

1.1

1.6

1.7

2.1

1.3

1.7

2.2

0.8

0.8

1.3

1.5

2.1

1.6

C20:l

8.3

8.1

6.2

8.4

6.2

6.1

6.5

4.9

8.4

5.2

7.0

6.4

6.9

6.5

6.3

G20:2
0.9

1.3

2.1

2.7

1.1

1.8

1.2

2.0

2.1

1.4

1.3

0.7

0.8

0.9

1.1

C20:3
0.8

1.
1

1.0

1.2

1.6

1.3

1.5

1.5

1.2

1.4

1.1

1.2

1.4

1.4

G20:4
0.6

0.5

0.8

1.0

1.1

1.2

1.0

1.0

0.6

0.6

0.7

0.6

0.8

C 21
:0

1.4

1.8

1.8

2.6

1.5

1.9

1.6

1.9

1.4

1.4

1.3

1.4

1.4

1.8

1.8

C22:l
9.1

7.7

5.9

7.1

7.2

5.2

7.1

5.2

5.4

6.5

7.4

8.0

7.3

8.4

9.7

C22:5
2.1

2.6

2.1

2.6

3.0

2.5

2.8

2.8

2.2

1.0

1.1

1.1

0.9

C22:6
9.5

7.6

5.5

7.5

11.5

8.9

10.2

5.4

6.4

9.0

7.9

11.4
11.8

10.9
10.3

*)

Values
expressed
as

fatty
acid

methylester.

163



164

Piskarev, A. J., Kaminarskaya, A. K. and Lukyanitsa, L. G. 1959. The application of glazing and low
temperature in the storage of frozen sprat. Proc. 10th Intern Congr. Refrig. 3.243. New York.

Varesmaa, Elina, Laine, J. J. and Niinivaara, F. P. 1968. Einfluss des Futters auf die Fettsäurezusam-
mensetzung der Regenbogenforelle (Salmo gairdnerii ) Z. Lebensm. Unters. u. Forsch. 138: 150—
154.

SELOSTUS

TUTKIMUKSIA SUOMESSA KASVATETUSTA KIRJOLOHESTA (S aimo irideus)

VII. Kirjolohen organoleptisen laadun ja rasvahappokoostumuksen muutokset
pakkasvarastoinnin aikana.

Elina Varesmaa, Jorma J. Laine & F. P. Niinivaara

Helsingin Yliopisto , Lihateknotogian laitos

Suoritetussa tutkimuksessa kirjolohet pakastettiin 40° C:ssa, jonka jälkeen puolet glaseerattiin
vedellä ja toinen puoli vakuumissa pakattiin polyethyleenipusseihin. Näytteitä säilytettiin 18° ja

32° C:n lämpötiloissa. Varastoinnin aikana kalojen laatua seurattiin organoleptisin arvosteluin ja
määrittämällä lipidien rasvahappokoostumus kaasukromatograafisesti.

Organoleptinen arvostelu osoitti, että kalojen säilyvyys oli ainoastaan 3 kk:tta ja että laatu oli hie-
man parempi 32° C:ssa kuin 18° C:ssa säilytetyissä kaloissa. Pakkaustapojen välillä sensijaan ci
esiintynyt suurempia eroja.

Rasvahappokoostumuksissa ei havaittu minkäänlaisia suurempia eroja varastoinnin aikana eikä korre-
laatioita esiintynyt myöskään pakkaustapojen ja varastointilämpötilojen välillä. Todennäköistä onkin, että
valkuaisaineissa tapahtuvat muutokset ovat pakkasvarastoinnin aikana lipideissä ilmeneviä muutoksia
huomattavasti merkittävämmät.

Tämän tutkimustehtävän nyt päättyessä pyydämme saada esittää Suomen Luonnonvaraintutkimus-
säätiölle parhaat kiitoksemme siitä taloudellisesta tuesta, jonka turvin tutkimustyö on suoritettu. Tutki-
mus on ollut meille erittäin mielenkiintoinen, ja toivomme, että siinä saavutetut tulokset tulisivat hyödyt-
tämään Suomen kalatalouden kehittymistä.