Comparative Analysis of Nutritional Components in Muscles between Wild and Cultured Masu Salmon Oncorhynchus masou

*

1. Beijing Aquatic Wildlife Rescue and Conservation Center, Beijing 102100, China; 2. Fisheries Technology Extension Station of Yanbian Korean Autonomous Prefecture, Yanji 133001, China

Abstract In this paper, approximate nutritional components and amino acid content were determined in muscles of female wild population (WP) with body weight of 2 500-3 000 g and female cultured population (CP) with body weight of 750-1 250 g masu salmon Oncorhynchus masou in the gonadal development stage IV by conventional method. The results showed that there were significantly higher crude protein and significantly lower crude fat in fresh muscle of WP than that in CP (P<0.05), but not significant differences in the contents of moisture and crude ash between WP and CP (P>0.05). Eighteen kinds of amino acids were detected in muscles of WP and CP, with higher total content of amino acids (TAA), essential amino acids (EAA) and four kinds of delicious amino acids (DAA) in WP than those in CP (P<0.05). The amino acid score (AAS) and chemical score (CS) revealed that the first limiting amino acid was tryptophan in two populations, with essential amino acid index (EAAI) of 75.59% in WP and 70.77% in CP. The findings indicated that the amino acid contents in muscles of CP are lower than that of WP, but the amino acid nutritional value evaluation indicators of both populations are very close, and both have high nutritional value.

Key words Oncorhynchus masou, Wild population, Cultured population, Amino acid composition

1 Introduction

Masu Salmo

Oncorhynchus

masou

is an anadromous migratory fish, mainly distributed in China, North Korea, Russia and Japan. During its life in freshwater, juvenile

O

.

masou

differentiates into two ecological populations, namely, migratory and land-locked populations, and land-locked populations live in freshwater rivers for their entire life. Japan has domesticated the land-locked population into an artificially cultured species, called

Oncorhynchus

masou

, and has obtained great economic benefits. China started to introduce

O

.

masou

in the late 1990s, and conducted research on biological characteristicsand artificial propagation techniques. Due to the continuous increase in fishing intensity and the changes in the ecological environment of the waters, the production of masu salmon migrating in the Tumen River and Suifen River in China has declined sharply, which has been unable to meet market demand. In recent years, fully artificial propagation and breeding technology research has been carried out on land-locked masu salmon collected from the Tumen River Basin, and excellent achievements have been made. The domestic land-locked masu salmon has gradually become a local special breeding target with high economic value.

At present, salmon and trout compound feed is mainly used to breed masu salmon, and changes in bait and living environment will affect its nutritional value and quality, which is very important for the large-scale breeding of masu salmon. However, so far, there has been no comparative analysis of the difference in nutritional quality between cultured and wild masu salmon populations. In view of this, we analyzed and compared the nutritional components in muscles between wild and cultured masu salmon populations to understand the nutritional differences between them, in the hope of providing basic data and theoretical basis for the future artificial breeding of masu salmon and the research and development of the feed.

2 Materials and methods

2.1

Materials

In this experiment, the wild masu salmon was collected from the main stream of the Tumen River, with a body weight of 2 500-3 000 g; the cultured masu salmon was taken from the Masu Salmon Aquatic Product Farm in Yanbian Korean Autonomous Prefecture of Jilin Province, with a body weight of 750-1 250 g. The number of samples of the both populations was 10 and both were female broodstocks in the gonadal development stage IV. The cultured populations were cultured in cement ponds with flowing water. The water source was the water of the Mijiang River, a tributary of the Tumen River. The water quality was high and the annual water temperature was in the range of 4-20 ℃, and the dissolved oxygen was ≥ 8 mg/L. The cultured populations were fed with the salmon and trout feed containing 40%-46% crude protein, 8%-12% crude fat, 14% ash and 5% crude fiber. Then, the muscles on the lateral scales and under the dorsal fin were taken for measurement.

2.2

Methods

The moisture was measured by the 105 ℃ drying constant weight method (GB/T 5009.3-2010); the protein was determined by the Kjeldahl method (GB/T 5009.5-2010); the fat was determined by the Soxhlet extraction method (GB/T 5009.6-2003); the ash content was measured by the high-temperature burning method (GB/T 5009.4-2010); the amino acid composition analysis was made with reference to the national standard (GB/T 5009.124-2003), after hydrolysis with 6 mol/L HCl, the amino acid composition was determined by Hitachi L-8900 amino acid analyzer, and tryptophan was determined by the high performance liquid chromatography (HPLC).

2.3

Nutritional

quality

evaluation

methods

Based on the amino acid scoring standard model (%, dry) recommended by the Food and Agriculture Organization and the World Health Organization (FAO/WHO) in 1973and the egg protein model proposed by the Institute of Nutrition and Food Hygiene, Chinese Academy of Preventive Medicine(%, dry), the amino acid score (AAS) was compared, and chemical score (CS) and essential amino acid index (EAAI) were used to evaluate the nutritional value of amino acids in muscles of wild and cultured masu salmons. The calculation formula is as follows:

AAS=test protein amino acid content (mg/g N), FAO/WHO scoring standard model amino acid content (mg/g N); CS=test protein amino acid content (mg/g N)/egg protein of the same amino acid content (mg/g N):

where

n

is the number of essential amino acids to be compared, A, B, C,... H are the essential amino acid content of fish muscle protein (%), AE, BE, CE,...HE are the essential amino acid content of whole egg protein (%).

2.4

Data

processing

Each group of data was expressed as mean ± standard deviation (mean±SD), SPSS 19.0 statistical software was used for data analysis, and Independent-Samples Test was used to analyze the differences between the data. When

P

<0.05, the difference was significant.

3 Results and analysis

3.1

Nutritional

components

in

muscles

of

wild

and

cultured

masu

salmon

As indicated in Table 1, There was no significant difference in moisture and ash content in muscles between wild and cultured masu salmon (

P

>0.05), the crude protein content of wild population was significantly higher than that of cultured population (

P

<0.05), and the crude fat content was significantly lower than that of cultured population (

P

<0.05). The nutritional value of fish mainly depends on the protein and fat content. The total protein and fat content of both populations were higher than 22%, and the difference was not significant.

3.2

Amino

acid

composition

and

content

in

muscles

of

wild

and

cultured

masu

salmon

In the experiment, 18 types of amino acids were detected in the two populations of masu salmon (Table 2), including 8 essential amino acids (EAA), 2 half-essential amino acids (HEAA) and 8 non-essential amino acids (NEAA). The content of 10 amino acids such as glutamic acid, lysine and arginine in the muscles of wild masu salmon populations was significantly higher than that in the cultured populations (

P

<0.05), and the difference in other types of amino acids was not significant. Besides, there were significant differences in the contents of total amino acids (TAA), EAA, HEAA and NEAA (

P

<0.05). Among the 18 types of amino acids measured, the content of glutamic acid was the highest, accounting for 2.76% and 3.07% of the fresh samples, followed by aspartic acid, lysine, leucine, alanine and arginine; the tryptophan content was the lowest, accounting for 0.08% and 0.10% of fresh samples, respectively. The content of delicious amino acids (glutamic acid, aspartic acid, glycine and alanine) in the muscles of wild masu salmon population was also slightly higher than that in the cultured population (Table 3).

Table 1 Content of general nutritional components in muscles of wild and cultured masu salmonOncorhynchus masou (n=10, g/100 g fresh weight)

Note: The values in the same column with different superscript letters indicate that there is a significant difference between the wild population and the cultured population of masu salmon (

P

<0.05), the same below.

Table 2 Content of amino acid composition and content in muscles of wild and cultured masu salmonOncorhynchus masou (n=10, g/100 g fresh weight)

Note:denotes essential amino acid,denotes half-essential amino acid,denotes delicious amino acid, TAA refers to total amino acid, EAA means essential amino acid, HEEA stands for half-essential amino acid, and NEAA means non-essential amino acid.

Table 3 Comparison of delicious amino acid content in the muscles of wild and cultured masu salmon Oncorhynchus masou with other fishes (n=10, g/100 g fresh weight)

Table 4 Comparison of human essential amino acid content (mg/g/N) in muscles between wild and cultured masu salmon Oncorhynchus masou with FAO/WHO pattern and egg protein (n=10)

3.3

Nutritional

value

evaluation

According to nutritional theory, after converting the data in Table 2 into milligrams of amino acids per gram of nitrogen, we compared them with the amino acid scoring standard model recommended by FAO/WHO and the amino acid model of whole egg protein (Table 4). It was found that the essential amino acid content of wild and cultured masu salmon

O

.

masou

was 2 722.62 mg/g/N and 2 483.44 mg/g/N, both lower than the egg protein standard of 3 066 mg/g/N, but higher than FAO /WHO standard 2 250 mg/g/N. As shown in Table 5, in muscles of wild and cultured masu salmon

O

.

masou

, except for tryptophan, the AAS of EAA was close to or greater than 1, and the CS was greater than 0.5. The AAS and CS of both populations were the highest in lysine (Lys) and the lowest in tryptophan (Trp); the amino acid evaluation results of both populations were the same, and the first limiting amino acid was

Table 5 Comparison of AAS, CS and EAAI values between WP and CP masu salmon Oncorhynchus masou

tryptophan (Trp). The EAAI of wild masu salmon

O

.

masou

was 75.59, slightly higher than that of the cultured population (70.77).

4 Discussions

4.1

Comparison

of

nutritional

quality

of

muscle

between

masu

salmon

.

and

other

fishes

The main nutritional part of fish is muscle, and the nutritional value of the same species of fish mainly depends on the content of protein and fat in the muscle. The total crude protein and crude fat content of masu salmon

O

.

masou

is higher than 22%, which is slightly higher than Atlantic salmon

Salmo

salar

and

Oncorhynchus

mykiss

, and much higher than many other freshwater fishes, so it is a high-quality fish with good nutritional value.The EAA content in fresh muscle samples of both populations of masu salmon

O

.

masou

was higher than that of Californian

Micropterus

salmoides

and

Pseudosciaena

crocea

, indicating that the masu salmon

O

.

masou

is a high-quality fish with high nutritional value. According to the ideal model of FAO/WHO, the better quality amino acids should contain about 40% of EAA/TAA, and EAA/NEAA should be more than 60%. In this experiment, the EAA/TAA of wild and cultured masu salmon

O

.

masou

were 39.64% and 39.33%, and the EAA/NEAA were 81.18% and 78.12%, respectively, which met the requirements of the ideal amino acid model, that is, the effect of amino acid balance is excellent.The fresh taste of fish meat depends on the composition and content of its delicious amino acids (glutamic acid, aspartic acid, glycine and alanine). In this experiment, the content of delicious amino acids in the muscle of masu salmon

O

.

masou

is very close to that of salmonids such as

O

.

masou

and

S

.

malma

, indicating that masu salmon

O

.

masou

has a very delicious taste. The CS evaluation system shows that the second limiting amino acids of the both populations were both methionine+cystine (Met+Cys). This result is consistent with the study by Xu Gefeng

et

al

.on

Brachymystax

lenok

, indicating that both populations have a slight lack of sulfur-containing amino acids, which may be related to the lack of sulfur-containing amino acids in their food.According to the study of Liu Shilu

et

al

., when the muscle fat content of fish reaches 3.5%-4.5% of the fresh sample, it will have good palatability. Besides, it was confirmed that the muscle fat content within a certain range is positively correlated with the flavor of the meat, that is, the flavor changes with the increase of muscle fat content. In this experiment, the muscle fat content of masu salmon

O

.

masou

(4.24%, 3.13%) is higher than that of common freshwater economic fishes such as

Ctenopharyngodon

idellus

(1.2%) and

Cyprinus

carpio

(2%),

Parabramis

pekinensis

(2.6%), and

Siniperca

chuatsi

(0.8%), which are the same as O. mykiss, S. salar, B. lenok,

O

.

masou

and other salmonids.

4.2

Analysis

of

nutritional

components

of

cultured

and

wild

masu

salmon

.

In this experiment, the muscle fat content of cultured masu salmon

O

.

masou

(4.24%) was higher than that of wild population (3.13%). This is consistent with the research conclusions of Sun Zhongwu

et

al

., possibly because migratory fish have a large living space, eat more types of live food, and consume relatively large energy, and therefore have low fat content. However, the activity space of the cultured population is small, and all the nutrition comes from the artificially prepared feed, which leads to higher fat content than the wild migratory population. The delicious amino acid content of the cultured population (6.20 g/100 g fresh weight) is lower than that of the wild population (7.02 g/100 g fresh weight), which is related to the food acquisition, and the result is the same as that of the

S

.

malma

. All the broodstock of the salmons die after reproduction. As the gonads develop, they need to consume a lot of protein and fat to meet the needs of gonadal development. The two populations of masu salmon

O

.

masou

samples tested this experiment are both sexually mature broodstock with gonadal development to stage IV. The muscle and taste are not optimal, and the main nutritional components may be reduced. The differences in muscle nutrition levels of masu salmon

O

.

masou

at different physiological stages need to be further studied.The results of this experiment have important significance for the demonstration and promotion of culture of land-locked masu salmon

O

.

masou

in the future. Although the two populations of masu salmon

O

.

masou

have different amino acid content in their muscles, their nutritional value levels are very similar, which provides favorable support for further demonstration and promotion of the cultured masu salmon

O

.

masou

population. With the gradual decline of wild masu salmon

O

.

masou

resources, more attention should be paid to research on the culture technology of land-locked masu salmon

O

.

masou

. As long as the special compound feed is continuously developed and optimized, and scientific and proper matching of its nutritional components and amino acid composition is made, the cultured masu salmon

O

.

masou

can completely replace the wild population and become another excellent species with great promotion potential among salmonids.