# Marine Bioactives and Their Application in the Food Industry: A Review
## 2 Marine Sources of Bioactive Molecules
### Marine Invertebrates
#### 2.3.4 Crustaceans  
The largest group of marine arthropods, the class crustacean, is made up of approximately 30,000 species. They are considered the most economically important class of marine arthropods with regard to their role in the global fisheries market and also make a substantial contribution to the discovery of novel natural ingredients. Marine crustaceans, including shrimp, crabs, lobsters, crayfish, and prawns, have gained great attention due to their abundance of biologically active compounds. The ratios of saturated, monounsaturated, and polyunsaturated fats in shellfish play a role in promoting a healthy diet. Additionally, the presence of high-quality proteins containing all the dietary essential amino acids is vital concerning the maintenance and growth of the human body. Moreover, even their exoskeleton shells are identified as rich sources of functional biopolymers such as chitin/chitosan. By-products of crustaceans are recognized as a rich source of many other compounds, including proteins, lipids, pigments (astaxanthin), flavors, and minerals [114; 115]. The exoskeletons of crustaceans comprised about 30-50% minerals (mainly calcium carbonate), 30-40% proteins, and 20-30% chitin, in addition to other compounds such as pigments (e.g., astaxanthin) and lipids [116]. Numerous biologically active compounds associated with shellfish species have been investigated over the decades. For example, peptides derived from crustaceans possess potential therapeutic effects due to their activity as immune modulators and antitumor and antimicrobial agents. In particular, the ACE inhibitory activity of peptides derived from shrimp (_Acetes chinensis_) and Izumi shrimp (_Plesionika izumiae_) was found to be most effective as compared to the peptide derived from terrestrial food sources [117; 118]. Moreover, protein existing in shrimp waste comprises essential amino acids and non-essential amino acids, approximately 56.8 and 43.2%, respectively, and their protein hydrolysates also have diverse applications, for example, in pharmaceuticals, human nutrition, animal nutrition, cosmetics, and even as a nitrogen source in the growth media for microorganisms [119; 120]. For example, shrimp shell discard hydrolyses revealed their potential for application in functional foods, nutraceuticals, and protein supplements, as well as in blood pressure-lowering applications, mainly due to their significant antioxidant activities [114]. Moreover, investigations by [PERSON] et al. [121] on mannis shrimp (_Squilla mannis_), caramote prawn (_Peneus kerathurus_), and crab (_Liocarcinus vernalis_) assessed the distribution of fatty acids, mainly n-3 PUFA and furan fatty acids, in the neutral lipid and phospholipids fractions. According to their findings, caramote prawn contained higher furan fatty acids, while the crab edible part represented the most valuable source of dietary omega-3 fatty acids, mainly EPA. Apart from this, carotenoids are also another essential bioactive constituent that is responsible for the color of marine crustaceans such as shrimp, lobster, and crab. Carotenoids occur either as free pigments or as carotenoproteins in invertebrates. The predominant types of pigments in crustaceans are caroten, hydrocarbon- and oxygen-containing carotenoids, and xanthophyll, which are mainly carotenoidoproteins, carotenoids [122]. In particular, the crustacean exoskeleton is a rich source of carotenoproteins, which are mainly responsible for the green or orange-red color in shore crabs (_Carcinus maneus_), the red color in prawns (_Pandalus borealis_), and the blue color in freshwater prawns (_Macrobrachium rosenbergi_) [123; 124]. Crustaceans can absorb the ingested carotenoids and metabolically alter their keto and hydroxy derivatives [125]. When considering the carotenoprotein complexes in crustacean tissues, prosthetic carotenoid groups in the ovaries/eggs of crustaceans are canthaxanthin, astaxanthin, or astaxanthin ester, while astaxanthin is predominant in their exoskeleton [115].