1. Introduction
With the improvement of consumption levels, more consumers are not satisfied with only demanding nutritional quality, but also have higher demands on the taste, toughness and freshness of food. In recent years, various aquatic products have gained great popularity among consumers and have become a unique culture on the table, characterized by their crispness and tenderness, texture and chroma, and delicious taste. More consumers are sparing no expense in pursuing their tastes. Muscle quality is a comprehensive evaluation index, which is mainly evaluated based on the two aspects of muscle nutrition and muscle flavor [
1]. It is important to analyze muscle quality indexes and explore ways to improve muscle quality to meet consumers’ demand for food production.
Current domestic and international studies on muscle quality have focused on the meat content, nutrient content, amino acid, fatty acid content, and textural properties of aquatic animals [
2,
3,
4]. The physicochemical properties of muscles, such as textural characteristics, meat color, water holding capacity (WHC), and pH are also important indicators for assessing muscle quality [
5,
6]. It has been found that the addition of various nutrients [
7,
8,
9,
10] and additives [
11,
12,
13] to feed can affect the nutrient, amino acid, and fatty acid content of the muscles of aquatic animals. Xu et al. [
14] showed that optimal amounts of dietary protein improved the physical (or chemical) flavor quality of grass carp fillets by increasing the shear force, pH, hydroxyproline, protein, lipid, free amino acid, and nucleotide content (5’ inosinic acid), and decreased cooking loss, cathepsin B and L activities, and lactate content. Myofiber content was approximately 15% higher in Atlantic salmon (
Salmo salar L.) fed high-protein diets than those fed low-protein diets [
15]. In a study on rainbow trout (
Oncorhynchus mykiss), the muscles of rainbow trout fed a high-protein diet had lower brightness levels and higher redness levels [
16]. Under normal conditions, most of the muscle coloration of aquatic animals is derived from carotenoids in feedstuffs, so the flesh color of aquatic animals can be influenced by feeding feedstuffs containing pigments [
5]. Astaxanthin is a non-vitamin-A-derived carotenoid with strong pigment deposition ability. Its use as a dye in aquatic animals improves the value of (a*) in the shell and muscle of black tiger shrimp [
17]. Furthermore, muscle quality varies significantly between species; for example, silver carp (
Hypophthalmichthys molitrix) has significantly lower meat quality than that of mandarin fish (
Siniperca chuatsi) [
18]. However, the assessment of muscle quality of aquatic animals is not unified. There are studies on nutrient composition and there are studies on textural properties, but there is not yet a unified standard. In addition, there are few comparisons of the muscle quality of different aquatic economic animals, and the reasons for the differences between them are not yet known.
Crayfish (
Procambarus clarkii), freshwater prawns (
Macrobrachium rosenbergii), pacific white shrimp (
Litopenaeus vannamei), black tiger shrimp (
Penaeus monodon), kuruma prawns (
Penaeus japonicus), river prawns (
Macrobranchium nipponense), and Chinese shrimp (
Penaeus chinensis) are the most consumed crustaceans in China. They are loved by the majority of consumers and have significant economic importance. Crayfish are widely distributed in various aquatic ecosystems due to their remarkable environmental adaptability and robust viability. Crayfish have rapidly developed in the industry in China in recent years due to their bright color, delicious taste, and rich nutritional value and the high opinion of consumers [
19]. China’s farmed production of crayfish reached 2.891 million tons in 2022. Freshwater prawns, with their rapid growth, extensive feeding habits, and short production cycles achieved a high production of 177,836 tons in 2022 [
20]. Pacific white shrimp are one of the most important commercial aquaculture species due to their rapid growth rate and resistance to adversity, accounting for about 80% of global shrimp production [
21], and they are farmed in China. Their production reached 1.340 million tons in 2022. Black tiger shrimp are one of the largest and fastest-growing commercial shrimps; they live mainly in the Indo-West Pacific region, the east coast of Hainan Island and the southeast coast of China, and are widely farmed in China [
22]. China’s farmed production reached 114.36 thousand tons in 2022. Kuruma prawns are a commercially important species in several countries, including China, Japan, and the Mediterranean regions around Egypt, Israel, and Turkey. Kuruma prawns are one of the largest penaeid prawns. Due to their high desiccation resistance, good taste, and rich nutritional content, kuruma prawns are one of the most economically important members of the Penaeidae family [
23]. China’s farmed production reached 46,199 tons in 2022. River prawns occur over a wide geographical range in East Asia. They are of significant importance as a commercial aquaculture species in China; China’s farm production reached 226,312 tons in 2022 [
24]. Chinese shrimp are one of the most economically important commodities in the global fishing industry. They are rich in nutrients needed by the human body and are preferred by consumers owing to their taste. China’s farmed production reached 30,929 tons in 2022 [
25]. However, the aquaculture industry faces issues such as intensive farming, high culturing density, and water quality that affect muscle quality; therefore, these issues, among others, need to be addressed.
Consequently, in this study, the muscle quality of these seven crustaceans species was more comprehensively evaluated and compared, and the differences between their muscle qualities were more comprehensively described to provide a reference for the study of muscle quality in aquatic animals.
4. Discussion
With the improvement of people’s living standards, more and more attention has been paid to the quality of crustaceans’ meat. This article selects seven main types of commercial crustaceans in China and makes a comprehensive assessment of their meat quality.
MC is one of the indexes for evaluating the quality, parental germplasm, and economic characteristics of aquatic products. It varies depending on the species, growth stage, living environment, and diet. In the present study, the body weight of crayfish was significantly higher than that of the other six
crustaceans species. Nevertheless, the MC of crayfish was the lowest. This may be related to the thickening of the crayfish carapace, strong chelate foot, developed appendage foot, gonad development, and other factors. This indicates that the MC of crayfish is lower than that of other commercial crustaceans and depends on the growth stage, living environment, and origin [
33]. Tian et al. [
34] concluded that the MC of crustaceans is influenced by the environment in which they live, and the results of this work are similar; for example, the MC of crayfish in the Dongting Lake area was 20.21% [
34] and that of crayfish in Nanwan reservoir area was 19.96% [
35]. In the present study, pacific white shrimp had the highest MC, indicating that they contained more edible parts. Whether the higher MC is due to higher muscle quality needs to be further investigated. The nutritional value and flavor of these seven
crustaceans species were also examined to determine differences in muscle quality.
The main nutritional component of crustaceans is muscle, and the nutrients in muscles are mainly protein and lipid, which are elementary indicators for evaluating muscle quality [
36]. In the present study, the crude protein content of the seven
crustaceans species was significantly higher than the crude lipid and ash content, indicating that crustaceans are a high-protein and low-lipid food [
37]. It is known that protein is an essential part of the diet of aquatic animals and is required for the growth, development, reproduction, and survival of fish. The amount of protein content could affect the growth and nutritional values in the muscle of crustaceans [
13,
38]. Pacific white shrimp, black tiger shrimp, and Chinese shrimp had the highest crude protein content, but no significant difference from freshwater prawns and kuruma prawns; crude lipid content was also the highest value for freshwater prawns and pacific white shrimp. Therefore, freshwater prawns and pacific white shrimp are high-quality edible crustaceans with high protein and lipid contents.
Protein consists of amino acids. EAA content is an important nutritional value index for muscle production [
39]. In the present study, the content of Thr was the highest in crayfish; Met and Lys were the highest in freshwater prawns; Ile and Leu were the highest in pacific white shrimp; His was the highest in crayfish and freshwater prawns; and Val and Phe were the highest in freshwater prawns and pacific white shrimp. In addition, umami amino acids (Phe, Ala, Gly, Asp, Glu, and Tyr) reflect the flavor of the muscle and are important indicators of muscle quality [
38]. In the present study, the UAA contents of pacific white shrimp, black tiger shrimp, and Chinese shrimp were the highest and significantly higher than those of the other four
crustaceans species, indicating that these three
crustaceans species have better flavors. Overall, crayfish, freshwater prawns, and pacific white shrimp have high nutritional values of amino acids; however, pacific white shrimp, black tiger shrimp, and Chinese shrimp have better flavor.
More and more attention has been paid to the crucial role of fatty acids and predominantly unsaturated fatty acids in the human body so as to reduce blood lipids, prevent cardiovascular diseases, and promote growth and development. The World Health Organization (WHO) reported that reducing the saturated fatty acid (SFA) content and increasing the UFA content in the human diet is part of effective nutrition and prevention of chronic diseases [
40]. In addition, PUFAs can significantly enhance the scent and reflect the juiciness of the muscle to a certain extent [
41]. In terms of fatty acid composition, the fatty acid types of crayfish, freshwater prawns, river prawns, and Chinese shrimp were higher than those of the other three
crustaceans species. The C18:3n-3, C20:4n-6, UFA, and PUFA contents had their highest values in crayfish, PUFA was highest in freshwater prawns, and C18:2n-6 had its highest values in freshwater prawns and pacific white shrimp. This shows that crayfish have the highest fatty acid value and strongest flavor, followed by freshwater prawns and pacific white shrimp. The highest content of SFA was palmitic acid (16:0), and seven of these were consistent. Palmitic acid can increase blood lipids and may cause the accumulation of blood cholesterol [
42]. The crude lipid content of the seven
crustaceans species was low, so palmitic acid would not cause nutritional problems. Recent studies have shown that MUFAs also play a role in regulating lipid metabolism, reducing the oxidation sensitivity of LDL cholesterol, protecting vascular endothelium, and reducing blood hypercoagulability [
43]. Oleic acid (18:1) was the most abundant MUFA among the seven
crustaceans species. Oleic acid is a benign fatty acid that can lower cholesterol and LDL [
44]. In this paper, crayfish, freshwater prawns, and river prawns had high levels of oleic acid. Therefore, among the seven
crustaceans species, crayfish have the highest nutritionally valuable fatty acids.
In addition to nutrients, the textural properties of muscle are important factors for their performance and represent the most important sensory and physicochemical index of muscle quality [
45]. Hardness is represented by the human body’s sense of touch—softness or hardness, the force required to deform a food, the internal bond that maintains its shape. The greater the hardness, the greater the deformation force required for fracture and the greater the springiness [
46]. Springiness can reflect the binding condition of prawn muscle tissue; the better the crucial ability, the higher the springiness. Both springiness and chewiness reflect the edible taste of prawn muscle [
47]. In this study, the hardness, cohesiveness, gumminess, and chewiness of pacific white shrimp were the highest. On the contrary, the hardness, springiness, gumminess, and chewiness of river prawns were all minimal. Overall, the pacific white shrimp had the best textural properties, while the river prawns had the worst textural properties.
One of the key characteristics of meat quality is muscle chroma, which can be identified through visual perception. Muscle chroma itself does not contribute much to muscle flavor but is considered as a fleshy trait primarily because it represents the external appearance of the physiological, biochemical, and microbial changes of the muscle itself. Ferrous myoglobin (Mb) and hemoglobin (Hb) play an important role in muscle color. Therefore, muscle chroma is still commonly used to indicate meat quality. Muscle chroma is typically represented by a brightness value (L*), redness value (a*), and yellowness value (b*), with the change in a* having the best correlation with muscle chroma sensation [
48]. In this study, the a* of crayfish, black tiger shrimp, and Chinese shrimp were significantly higher than those of the other species, except for kuruma prawns, suggesting that crayfish, black tiger shrimp, and Chinese shrimp have better visual indication of quality.
The amount of WHC is directly related to muscle texture and nutritional composition. The loss of water deprives the muscle not only of moisture but also nutrients and heme, affecting the sensory morphology and flesh color of the muscle [
14]. Therefore, cooking loss rate and drip loss rate are essential parameters that reflect muscle water retention and show a negative correlation to quality [
49]. In this study, the cooking loss of pacific white shrimp and river prawns was significantly higher than that of the other four
crustaceans species except freshwater prawns, which is consistent with the study by Cui et al. [
50], which showed that pacific white shrimp and river prawns lose more nutrients after cooking. The drip loss of river prawns was significantly higher than that of the other six
crustaceans species, and the structural parameters of the hardness, springiness, and chewiness properties of river prawns were the lowest among the seven groups. Relevant studies also showed that drip loss is negatively correlated with the textural characteristics of muscle hardness, springiness, and chewiness [
51], which was consistent with the results of this study. This also explains the high drip loss of river prawns. The pH value of muscle has a significant influence on muscle quality. When the pH of muscle decreases to the electrical value of the muscle protein or protein denaturation occurs, the mechanical properties of muscle are directly affected, especially retention, cooking loss, and dry processing capacity [
52]. In the present study, the pH value of kuruma prawns was the highest. Still, it was not significantly different from that of freshwater prawns, river prawns, and Chinese shrimp. In contrast, the pH of crayfish was significantly lower than that of the other six species, suggesting that kuruma prawns, freshwater prawns, river prawns, and Chinese shrimp would be better preserved, boiled, and processed, while the opposite was true for crayfish.