COMPARISON O F T H E AMINO ACID COMPOSITION O F FIFTEEN SPECIES O F WHOLE FISH

A COMPARISON O F T H E AMINO ACID

COMPOSITION O F FIFTEEN SPECIES O F WHOLE FISH

LEIF REIN NJAA a n d FINS UTNE

Institute o f v i t a m i n Researclr Uirectoratc of Fisheries, N-5013 Bergen, Norway

ABSTRACT

With the object of obtaining information on the nutritive \ d u e of whole fish as feed for fur animals and in fish farming 47 samples of 15 species of fish were a~lalysed for the amino acid contents. T h e samples were analysed for nitrogen, ash, T M A O , T M A and total volatile nitrogen and prepared for amino acid analysis by freeze-clrying followed hy e x t r a c t i o ~ ~ with l~exane. I11 23 cases both wet samples and hexane extracted dry samples were analysed, establishing that the latter were representative of the whole fish as received. For two species, saithe and blue whiting, both whole and gutted fish were analysed giving quite co~iiparable results. T h e amino acid c o ~ ~ t c ~ ~ t s between species \?ere I-cmarkahl>- similar. T h c note\vorthy cscrptions t\.crc a hig11 content of glycine in saithe a n d a high content of histidine in pelagic species, especially in mackerel.

I N T R O D U C T I O N

A project on the analysis of nutrients in Norwegian fish spccics and fish products was sponsored by the Norwegian Council for Fisheries Research for the years 1973-1975. Results were published at intervals in c<Fiskets Gangn (UTNE, 1976). T h e amino acid analyses of 15 species of fish are compiled a n d discussed in the present paper. Data on the fatty acid composition of the fish lipids were published by L;\MBERTSES (1978) and d a t a on mineral contents by

JULSHAMN et al. (1978).

Most samples consisted of whole fish, but in a few cases samples of gutted fish were analysed. Values for whole fish were relevant as thc anticipated use of the d a t a was for the evaluation of such fish as feed for fur animals and in fish farming. Amino acid analyses of fish off-fall products have been published previously (NJAA, 1978).

SAhlPLES

T h e samples were obtained during the years 1973-1975 and brought to the institute fresh, frozen or in ice. They were in good condition as indicated by

Table I . Mesa values and standard deviations for ash, TMAO-N, TMA-S and total volative N in the fish species analysed for amino acids.

Ash TMAO-?J TMA-K Total vol. S

(glkg

dry weight) (mg1100 wet weight) Saithe, whole

Saithe, gutted Blue whiting, whole Blue whiting, gutted Norway pout Polar cod Capelin

Herring, local stock Herring, North Sea Sprat

Mackerel Horse mackerel Sandeel

Great Silver Smelt Muller's pearlsides Ballan Wrasse Lumpfish (female) Lumpfish (male)

* Number of samples analysed.

low values of trimethylamine and high values of trimcthylamine oxide (Table

, 1). T h e samples were honiogcniscd by several passcs through a meat grirldcr a t low temperatures a n d representative portions were freeze-dried. After drying most of the fat was extracted with hexane and the residue was milled in a Tecator mill. T h e extracted freeze-dried samples were stored for analysis.

T h e 1973-samples were also arlalysed aficr lloniogcilisatioll without drying.

This was done to establish whether freeze-dried samples were representative of the original fish.

IIETHOIIS

Protein ( N x 6,25) was dctcrniinccl esscntiall>- as dcscrihrd by CRCIOKE and SIMPSOX (1971) after digestion in a Tecator block digestor at above 370". Ash, T M A O , T M A a n d volatile N were determined with conventional methods.

Amino acids were determined firstly in a Techllicon Amino Acid Analyser Model NC-I a n d later in a Model NC-2-P. I n thc former case the samples were hydrolysed with 6 M HCI under reflux in a N p atmosphere, in the latter

Table 2. Gomparisotl of amino acid analyses on 23 wet and 23 freeze-dried samples of fish. (Means +-standard deviations).

Wet Freeze dried

samples samples

glkg protein Aspartic acid

Threonine Serine Glutamic acid Proline Gly cine Alanine Valine Cys tine (n=20) Methionine Isoleucine Leucine Tyrosine

Phenylalanine ( n = 22) Lysine

Histidine Arginine

case with 6 M H C 1 in closed screw cap test tubes with TiC13 added to protect methionine (MOORHOUSE et al., 1976). However, the methionine analyses were erratic, a n d the tables therefore contain further values obtained colori- metrically by the metod described by NJAA (1980) for total methionine.

RESULTS

Comparisons of results obtained on wet samples a n d on samples after freeze-drying a n d fat extraction are given in table 2. Most differences were small a n d insignificant, only aspartic acid (p<0.05) and cystinc (p<0.01) showed values slightly higher in the freeze-dried samples. I n our hands values for these amino acids tend to vary between analyses of the same sample a t different times. W e therefore concluded that analyses of extracted freeze-dried samples were representative for the original samples and in the two later years only extracted dry samples were used for analysis. T h e amino acid composi- tion for four species of the Gadidae family are given in table 3. T h e samples of saithe a n d blue whiting were a n a l ~ s c d wholc and gutted. For practically all

Table 3. Amino acid contents (glkg protein) in four species of cod fishes, (Gadidae)

Saithe Blue whiting Norway Polar

Whole Gutted Whole Gutted pout cod

Whole Whole

(3)* (3) (3) (2) (4) (2)

Aspartic acid Threonine Serine Glutamic acid Proline Glyqine Alanine Valine Cystine

Methionine (chrom.) Methionine (color.) Isoleucine

Leucine Tyrosine Phenylalanine Lysine Histidine Arginine Tryptophan

* Number of samples analysed.

Table 4. Amino acid contents (glkg protein) in seven species of pelagic fish used for the production offish meal and oil.

Aspartic acid Threonine Serine Glutamic acid Proline Glycine Alanine Valine Cystine Methionine

(chrom.) Methionine (color.) Isoleucine Leucine Tyrosine Phenylalanine Lysine Histidine Arginine Tryptophan

Capelin (4) *

I-Ierring North Sea

(3)

Herring Local stock

(3)

Sprat (3)

* Number of samples analysed

Table 5. Amino acid contents ( g l k g protein) in four miscellanrous fish species Great

Miiller's Ballan Lumpfish Lumpfish silver pearlsides wrasse female male smelt

(3)* (4) (2) (2) (2)

Aspartic acid Threonine Serine Glutamic acid Proline Glycine Alanine Valine Cystine Methionine (chrom.) Methionine (color.) Isoleucine Leucine Tyrosine Phenylalanine Lysine Histidine Arginine Tryptophan

*

amino acids the values were strikingly similar between species, and also between whole and gutted fish. Only glycine showed somewhat divergent values in saithe as compared to the other species.

T h e amino acid composition in samples from seven species of pelagic fish is given in table 4. These fish species are exploited for the production of fish meal and oil. Again the results were strikingly similar hetwecn specics, the only exception being the high value for histidine in mackerel.

T h e amino acid composition of four species of miscellaneous fish species are given in table 5. Ballan wrasse and lump-fish (female and male) showed high values for glycine. Besides, some of the amino acid values differed greatly between samples within the same species (glutamic acid for great silver smelt and for Miiller's pearlsides, glycine for Miiller's pearlsides and leucine for lumpfish).

DISCUSSION

Most d a t a reported previously 011 the amino acid composition of different fish species refer either to the edible part of the fish (COSNEI~L and HO'~\'G!\TE,

1959; BREKKAN a n d BOGE, 1962) or to fish meals (NJAA et al. 1968; O P S T V E ~ T et al. 1970). A R N E S E N ( ~ ~ ~ ~ ) reported d a t a on codfish organs, flesh, bones a n d stomach contents, but not on whole cod. T h e samples analysed in the present study were probably best comparable with whole fish meals, assuming that the production processes d o not scriously affect the amino acid composition.

Data given by BOGE (1960) indicate that this is the case at least in a comparison between whole herring a n d whole herring meal. O u r finding of surprisingly small differences between the amino acid contents of different fish species should also be judged on the basis of thc variation seen between fish meals produced from one species. T h u s mcnhaden meals ( K I F E R ct al. 1968), Norwegian herring meals (KII'KR ct al. 1969) and Canadian Atlantic herri~lg meals (POWER et al. 1969) showed coefficients of variation below 10% for most of the amino acids, a n d quite similar amino acid contents. Likewise, d a t a on the amino acid contents reported by OPSTVEDT et al., (1970) for fish meals from five species of pelagic fish were very similar a n d the coefficients of variation for most amino acids were less than 10%. I n contrast, the amino acid contents of fish off-fall from cod varied much more with coeff~cients of variation ranging from 14 to 66%. Also, the contents of most of the essential amino acids were lower than in whole fish (NJAA, 1978).

T h e higher content of glycine in saithe than in thc other Gadidae may be due to the relative amounts of flesh to bones, skin, etc. (ARXESES, 1969.) I n fact, in our material there was a positive correlation between the glycine content and the amount of ash o n a dry matter basis. I n a n earlier study we found a rather high level of glycine in horse mackerel (scad) together with a high ash content (N~JAA et al., 1968). I n the present study one sample of horse mackerel had a rather low ash content a n d was not especially rich in glycine (Tables 1 a n d 4).

Ballan wrasse a n d lumpfish showed high contents of glycine as well as of ash (Tables 1 a n d 5 ) . T h e former is a bony fish with thick skin, the latter apparently contains much cartilage. T h e high content of histidine in mackerel is a consequence of this species containing high levels of free histidine in the musclc. SAKAC;UC:HI a n d S ~ r n r r z u (1965), Ijli.l:titi:\s and B o c ; ~ (1962) and KJOSBAKKEN a n d L , - i ~ s m (1 98 1 ) reported high lcvels of total histidine in the edible part of mackerel. T h e free histidine content in mackerel and herring varies with the season (SAKAGUCHI a n d SHIMIZU, 1965; HUGHES, 1959), the high content in herring meals reported by PO\VER et al. (1969) may be a reflection of this. Species with high levels of free histidine should be stored with care as adverse storing conditions may result in the formation of histamine (TAKAGI et al. 1969).

Among the fish species analysed only iumpfish seems to have significantly lower levels of most of the esse~ltial ammo aclds comparrd to those 111 othrr species. Mean values for the amino acid contents found in 12 analyses of whole fish of the Gadidae family and in 17 analyses of whole pelagic fish are compared in table 6. T h e only noteworthy difference was found for the contents of histidine (p<0.001). Capelin, which is a salmoid species showed values nearer to the Gadidae than did the other pelagic species.

Table 6. Comparisons between the mcan contents of amino acids (glkg protein) in 12 samples of whole fish 60111 the Gadidae family and in 17 samples of hole pelagic fish.

Gadidae Pelagic Significance

of difference

Aspartic acid 99.1 2 8.6

Threonine 45.7-t 4.0

Serine 46.32 3.7

Glutamic acid 132.5511.7

Proline ( l o ) * 40.82 4.2

Glycine 62.42 10.1

Alanine 6 1 . 7 t 3.3

Valine 45.62 3.2

Cystine ( 1 1) 8 . 0 2 1.9 Methionine (chrom.) ( 1 1) 28.52 3.0 Methionine (color.) 32.42 1.2

Isoleucine 40.72 3.8

Leucine 71.85 3.4

Tyrosine 32.02 2.9

Phenylalanine 38.22 2.3

Lysine 85.65 10.2

Histidine 19.82 1.6

Arginine 61.75 3.3

Tryptophan 10.02 0.9

p < 0.05 N.S.

p < 0.01 p < 0.01 N.S.

N.S.

N.S.

N.S.

p < 0.05 N.S.

p < 0.05 K.S.

N.S.

N.S.

N.S.

N.S.

p < 0.001 p < 0.05

N.S.

* Samples analysed when less than 12, resp. 17.

N.S.: not significant.

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