Crabs are a globally consumed delicacy, recognized for their unique flavor and nutritional composition. This article explores various aspects of crab diets, ranging from the nutritional value of different crab species to the potential health benefits and the impact of diet on crab quality. The discussion encompasses the nutritional composition of both natural crab meat and crab-flavored seafood (CFS), also known as imitation crab.
Crab-Flavored Seafood (CFS): A Nutritional Overview
Crab-flavored seafood (CFS) is a processed food product designed to mimic the taste and texture of crab meat. It is a well-known traditional Japanese product that is sold as “imitation crab” worldwide. Developed in Japan in the 1970s as an alternative to crab leg meat, CFS quickly gained popularity in Asian countries and later in the United States and Europe. In these regions, it is often used as an ingredient in dishes like California rolls and seafood salads.
Nutritional Profile of CFS
CFS is generally considered a low-cost, low-fat, and high-protein food. A study involving Sprague-Dawley rats fed a normal diet with 5% dried CFS for 84 days showed interesting results. While there were no significant differences in food intake, overall body weight, or organ weight between the control group and the CFS-fed group, the muscle weight of rats consuming CFS tended to be higher. Additionally, serum high-density lipoprotein (HDL), total bilirubin (T-BIL), and indirect bilirubin (I-BIL) levels were significantly elevated in the CFS group.
Potential Health Benefits of CFS
The consumption of CFS may promote muscle protein synthesis and improve serum biomarkers associated with disorders such as cardiovascular disease and stroke. This suggests that incorporating CFS into the diet could offer certain health advantages.
Composition of CFS
Commercial CFS, such as KIBUN CFS, is typically made from minced fish and surimi pollack ground with salt, starch, egg white, and other ingredients. The mixed fish paste is formed into a sheet and steam-heated at 89°C for 2 minutes 30 seconds during production.
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Amino Acid and Fatty Acid Content in CFS
Dried CFS contains approximately 40.30% total protein, with essential amino acids such as leucine (3.24%), valine (2.07%), and isoleucine (1.86%). It also contains methionine at 1.15%, which is higher than the levels found in other fish paste products. In terms of fatty acids, dried CFS contains 0.93% omega-3 and 2.89% omega-6 fatty acids. It is also rich in oleic acid (OA; 1.96%) and linoleic acid (LA; 2.84%).
Carotenoid Content in CFS
HPLC analysis has revealed the presence of carotenoids in dried CFS, including capsanthin, β-cryptoxanthin, lycopene, and β-carotene. An unidentified compound, possibly cryptocapsin, was also detected.
CFS in Rat Diets
In a study where rats were fed a diet containing 5% CFS, the CFS replaced casein, L-cystine, and β-cornstarch in the AIN-93G diet. This substitution may contribute to the observed effects on muscle protein synthesis.
Impact on Serum Biochemistry
After 84 days of CFS administration to rats, several changes in serum biochemistry were observed. Blood urea nitrogen (BUN) levels were significantly lower in the CFS-fed group, while potassium (K), calcium (Ca), inorganic phosphorus (IP), HDL-C, T-BIL, and I-BIL levels were significantly raised.
Potential Anti-Fatigue Activity
The study indicated that CFS might have anti-fatigue activity. After 12 weeks, BUN levels were decreased by 27% in the CFS group compared to the control group, and serum aspartate aminotransferase (AST), alanine transaminase (ALT), and lactate dehydrogenase (LDH) levels tended to be lower.
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Effects on Lipid Metabolism
Rodents fed CFS showed higher HDL-C levels and lower triglyceride (TG) and atherogenic index of plasma (AIP) levels. These findings suggest that CFS may protect against hyperlipidemia and heart disease.
Nutritional Value of Natural Crab
Crab meat is known for its valuable nutritional properties, including essential amino acids, minerals, and vitamins. Lipids, particularly n-3 polyunsaturated fatty acids (PUFAs), are also important components of crab's nutritional value.
Lipid Composition of Different Crab Species
A study comparing the lipid molecular species compositions of the Japanese mitten crab (Eriocheir japonica) and the red king crab (Paralithodes camtschaticus) revealed significant differences. TGs were the main class of lipids in the crab hepatopancreas, while they were found in trace amounts in muscle. The Japanese mitten crab differed from the red king crab by a higher content of 16:0, 16:1, 18:2, and 20:4 fatty acids (FAs) and a lower content of eicosapentaenoic and docosahexaenoic acids.
Molecular Species of Lipids
In the muscles and hepatopancreas of E. japonica, 151 and 196 lipid molecular species were found, respectively. The TG compositions of the hepatopancreases from the studied crabs had significant differences, with E. japonica containing 98 molecular species of TG and P. camtschaticus containing 59.
Phospholipid Composition
The PE consisted primarily of eicosapentaenoic (C20:5, EPA) and docosahexaenoic acids (C22:6, DHA) in all the samples studied. The muscle and hepatopancreas samples of E. japonica were distinguished by a different level of alkylacyl PE: C20:5 PE and C22:6 PE.
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Health Implications of Crab Lipids
The high content of molecular species of lipids with n-3 polyunsaturated fatty acids in crabs E. japonica and P. camtschaticus confirms their high nutritional value. N-3 PUFAs are known to significantly improve mental development and maturation of visual function, especially in utero and in early childhood.
Seafood in General: A Nutrient-Rich Food Source
Seafood is a rich source of various nutrients, including vitamins, minerals, and omega-3 fatty acids. It is also a high-quality protein source.
Nutrients of Public Health Concern
The Dietary Guidelines for Americans 2020-2025 identified vitamin D, calcium, potassium, and dietary fiber as dietary components of public health concern. Seafood can be a significant source of vitamin D, calcium, and potassium.
Vitamin D in Seafood
Fatty fish are a natural source of vitamin D3. Fatty fish can contain between 5 and 15 µg of vitamin D (200-600 IU) per 100 g portion. Atlantic herring can contain as much as 41 µg (1,600 IU) per 100 g portion.
Calcium in Seafood
Seafood contributes about 3 percent of dietary calcium in the United States. Calcium absorption may be enhanced by the protein and vitamin D provided by fatty fish.
Potassium in Seafood
Potassium content varies by species. For example, salmon can contain 280-535 mg/100 calories, and clams offer 534 mg/100 calories.
Protein in Seafood
Seafood is a protein source of high biological value. Replacing other animal protein sources with seafood could lead to higher nutrient intake without reducing total protein intake.
Omega-3 Fatty Acids in Seafood
Seafood is a primary dietary source of the n-3 LCPUFAs, EPA and DHA. These fatty acids are essential for fetal development and are key components of all cell membranes, especially in the brain and retina.
Selenium in Seafood
Selenium (Se) is an essential nutrient that functions as a component of selenoproteins, which are critical in DNA synthesis and serve as oxidative defense enzymes in the immune system.
Impact of Diet on Crab Quality
The quality of crustacean aquatic products is significantly affected by diet. Cholesterol (CHO), an essential element for crustacean growth, is often supplemented in their diet.
Effects of Dietary Cholesterol
Different dietary CHO levels can significantly increase lipid content in the hepatopancreas and promote the accumulation of n-3 long-chain polyunsaturated fatty acids (LC-PUFA) in the hepatopancreas and muscle. However, high dietary CHO levels can decrease protein content in muscle.
Impact on Flavor Quality
A 1.00% CHO treatment can result in higher relative levels of volatiles, producing grassy, fruity, and fatty odors in muscle. Dietary CHO can also weaken nucleotide and free amino acid accumulation in hepatopancreas and muscle.
Rocky Shore Crab Diet
The tropical rocky shore crab Grapsus albolineatus primarily feeds on filamentous algae but also consumes animal matter whenever available. The crab's diet switches to encrusting algae during the summer due to a die-off of filamentous algae, influencing the crab's fitness.
Nutritional Impact on Crab Fitness
The nutritional quality of diets significantly affects crab survival and molting. Crabs fed on a nutritionally superior diet of algae and meat exhibit enhanced growth, higher levels of energy in the reproductive organs, and stored more energy in the hepatopancreas.