Marine Antioxidants from Marine Collagen and Collagen Peptides with Nutraceuticals Applications: A Review

Collagen peptides and marine collagen are enormous resources currently utilized. This review aims to examine the scientific literature to determine which collagen peptides derived from marine sources and which natural active antioxidants from marine collagen have significant biological effects as health-promoting nutraceuticals. Marine collagen is extracted from both vertebrate and invertebrate marine creatures. For vertebrates, this includes fish skin, bones, scales, fins, and cartilage. For invertebrates, it includes mollusks, echinoderms, crustaceans, and poriferans. The method used involved data analysis to organize information for isolating and identifying marine biocompounds with antioxidant properties. Specifically, amino acids with antioxidant properties were identified, enabling the use of hydrolysates and collagen peptides as natural antioxidant nutraceuticals. The methods of extraction of hydrolyzed collagen and collagen peptides by different treatments are systematized. The structural characteristics of collagen, collagen peptides, and amino acids in fish skin and by-products, as well as in invertebrate organisms (jellyfish, mollusks, and crustaceans), are described. The antioxidant properties of different methods of collagen hydrolysates and collagen peptides are systematized, and the results are comparatively analyzed. Their use as natural antioxidant nutraceuticals expands the range of possibilities for the exploitation of natural resources that have not been widely used until now.


Introduction
Nutraceuticals have garnered significant attention for their role in alternative treatments for disease prevention and health maintenance.In the European Union (EU), there is specific legislation governing the marketing of functional foods and nutraceuticals, emphasizing their "safety" [1].The scientific risk assessment is carried out by the European Food Safety Authority [1].The impact of the COVID-19 pandemic required serious analysis to assess the extent to which dietary supplements and nutraceuticals had potential in the COVID-19 crisis [2,3].Nutraceuticals are those nutritional products that have additional health benefits [4,5].Nutraceuticals not only supplement the diet but also contribute to the prophylaxis or treatment of a disorder or disease [6].Nutraceuticals with antioxidant potential have gained wide interest.In the body, by-products of normal metabolic reactions such as normal cellular respiration and responses to external stimuli on cells generate reactive oxygen species (ROS), which are highly oxidative [7].Reactive species can be singlet oxygen, hydroxyl radical, superoxide anion, peroxide, and nitrous oxide.Long-term exposure to oxidative stress impairs the biosynthesis of molecules and causes some chondral diseases [8].Excessive accumulation of ROS damages cell membranes and biological macromolecules, causing damage to tissues and organs, and can generate various pathological conditions such as aging phenomena, arthritis, Alzheimer's, cancer, and other degenerative diseases [8,9].To stop such accumulations and maintain the average level of ROS species in the body, antioxidants are needed [10,11].Synthetic antioxidants including butylated hydroxytoluene (BHT), butylated butylated hydroxyanisole (BHA), and tertiary butylated hydroquinone (TBHQ) are the best known.Although they are compounds with remarkable antioxidant potential, they have shown increased toxicity and their use has begun to be restricted [11].Under these conditions, natural antioxidants have attracted attention [12].Compounds with antioxidant capacity from marine resources have gained wide interest, including those from marine fish, seaweed, jellyfish, and mollusks [13][14][15][16].Among the natural compounds with good antioxidant action and outstanding degradability, the following have stood out: alongside polysaccharides and collagen, gelatin, and collagen peptides [17][18][19].Native collagen, collagen hydrolysates, and gelatin have gained new potential uses due to their biocompatibility.These include applications as a food source and in various biological and medical domains [20][21][22].Additionally, they are utilized as biomaterials for medical purposes and in food packaging [23,24].For a long time, collagen was extracted from terrestrial sources like cattle and pigs.As shown by Lim et al. (2019) due to religious restrictions (Muslims, Hindus, and Jews avoid products from these animals) and the emergence of communicable diseases such as bovine spongiform encephalopathy (BSE), foot-and-mouth disease (FMD), and transmissible spongiform encephalopathy (TSE), which have become prevalent worldwide in recent decades, attempts have been made to search for other sources of collagen [25].Terrestrial animal products can transmit these diseases (Salvatore et al., 2020) [26].Thus, collagen from marine resources began to gain great importance.To avoid this risk, Geahchan et al. (2022) and Prelipcean et al. (2022) recommend using marine collagen in wound healing [27,28].There was an urgent need to identify new alternative sources of collagen.Recent studies on the molecular structure and biochemical properties of fish collagen have shown several similarities to collagen from terrestrial mammals.However, fish collagen has a lower molecular weight and a lower denaturation temperature than mammalian collagen as observed by de Melo Oliveira et al. (2021) and El Blidi et al. (2021) [29,30].Marine collagen has been studied for applications in different fields: biomaterials, Gallo [31][32][33][34][35][36][37][38][39][40].The marine environment offers a vast resource for isolating collagen and collagen peptides, often wasted as by-products from fish and invertebrate organisms.At present, these resources remain underutilized.In conclusion, the potential of marine-derived collagen antioxidants as valuable nutraceuticals is not fully recognized.This review aims to gather and organize information on techniques for isolating and separating collagen and collagen peptides from marine organisms, both vertebrates and invertebrates, while emphasizing their antioxidant properties.Specifically, it explores the potential of using fish by-products-such as skin, bones, scales, swimming fins, and fish heads-which are rich in collagen and collagen peptides but are currently underutilized globally.The data presented cover the structure and amino acid composition of collagen and their associated antioxidant properties.Results from various analytical methods demonstrate the antioxidant activity of marine collagen products.In addition, The diversity and potential were highlighted by de Melo Oliveira et al. (2021) and Rahman (2019) [29,41].Marine collagen can vary significantly in structure, depending on its source.It is worth noting that marine vertebrates, such as marine fish, possess more intricate skeletal systems with abundant collagen in their bones and skin.This observation is supported by Cherim et al. (2019) and Prajaputra et al. (2024) [42,43].Currently, a major problem in the fish farming industry is the inadequate management of waste or byproducts resulting from improper fish processing, which leads to economic losses and environmental problems.

Extraction Procedures
Biotechnologies used to extract collagen from marine organisms have been detailed in studies by Prajaputra et al. (2024) and Jafari et al. (2020), who categorized them based on the extracted collagen type.These methods include alkali-soluble collagen (SSC), acidsoluble collagen (ASC), enzymatic methods (PSC), and ultrasonic methods [43,44].The diversity and potential were highlighted by de Melo Oliveira et al. (2021) and Rahman (2019) [29,41].Marine collagen can vary significantly in structure, depending on its source.It is worth noting that marine vertebrates, such as marine fish, possess more intricate skeletal systems with abundant collagen in their bones and skin.This observation is supported by Cherim et al. (2019) and Prajaputra et al. (2024) [42,43].Currently, a major problem in the fish farming industry is the inadequate management of waste or by-products resulting from improper fish processing, which leads to economic losses and environmental problems.

Extraction Procedures
Biotechnologies used to extract collagen from marine organisms have been detailed in studies by Prajaputra et al. (2024) and Jafari et al. (2020), who categorized them based on the extracted collagen type.These methods include alkali-soluble collagen (SSC), acid-soluble collagen (ASC), enzymatic methods (PSC), and ultrasonic methods [43,44].Additionally, Cherim et al. (2017) and Lu et al. (2023) have reported on the isolation and characterization of collagen from marine sources [45,46].Depending on the chosen extraction method, collagen products vary in different yields and properties.Marine collagen extraction typically involves two primary steps: I.
The pre-treatment stage involves preparing the raw material and eliminating contaminants to ensure the purity of the final product.Marine by-products, including skin, bones, scales, or the head and appendages of marine organisms in the case of invertebrates, are carefully selected.Various compounds, such as pigments, non-collagenous proteins, and unwanted lipids, are removed during this stage, as documented by Ampitiya et al. (2023) [47].Additionally, other researchers, such as Wang et al. (2018) and Chen et al. (2021) have reported successful removal of adhesive residues using aqueous NaCl solutions of varying concentrations [48,49].Cumming et al. (2019) reported the removal of inorganic minerals by demineralization with EDTA (ethylenediaminetetraacetic acid), as reported [50].Another option was the use of a 0.5 M HCl solution, which was reported by Xu et  reported that fermentation is also an alternative pretreatment that helps to obtain collagen from Nile tilapia skin by the PSC process with very good purity [55].II.The actual extraction stage can be carried out by specific methods.The most commonly used methods for obtaining collagen are the ASC and PSC methods [43,56].
The ASC procedure is the most widespread.Sirbu et al. in 2019 reported studies on the validation of a quantitative method for the extraction of collagen from the skin of gray mullet fish by the ASC process [57].For the extraction of collagen from the tissues of marine organisms, acetic acid is the most widely used dilute acid, but other acids can also be used, such as citric acid, lactic acid, or chloroacetic acid.In 2020, Senadheera et al. and in 2021, Shaik et al. showed that organic acids provide higher collagen extraction efficiency than inorganic acids [58,59].The most widely used ASC extraction method is the one using acetic acid in a 0.5 M concentration, continuously stirred between 24 h and 72 h, for collagen extraction [43,56].From multiple reported studies, it appears that in order to obtain the best extraction results, the acetic acid concentrations must be adapted to the sample type.Thus, Hadfi et al. (2019) extracted collagen from silver catfish (Pangasius sp.) skin with different concentrations of acetic acid (0.5 M and 0.7 M) and reported yields of 10.9% and 5.47%, respectively [60].So, there was a higher yield when 0.5 M acetic acid concentrations were used [60].However, Baderi N.A. et al. (2019) extracted collagen from shortfin scad (Decapterus macrosoma) and reported 1.01% and 1.31% yields when using 0.5 M and 0.7 M acetic acid, respectively, so the yield was higher at 0.7 M acetic acid concentrations [61].In the following step, the collagen supernatant is obtained by centrifugation, which then has to be precipitated with salt (NaCl).This separates the collagen precipitate.In 2020, Seixas et al. reported these methods along with other procedures for the extraction of collagen from elasmobranch by-products for potential biomaterial use [62].In 2018, Tanaka et al. isolated collagen from bluefin tuna (Thunnus orientalis) skin, and Tan et al. isolated collagen from channel catfish (Ictalurus punctatus) skin [63,64].
The PSC procedure is also a commonly used process and is based on the reaction of collagen with pepsin.Venkatesan et al. (2017), showed that in this treatment, the enzymes provide increased yields and purity of collagen [65].Zhao et al. (2018) showed that acidsoluble collagen tends to generate a lower yield, and pepsin extraction increases extraction yield because pepsin cleaves crosslinks in the telopeptide region, thus producing increased collagen solubility in acid [66].Castaneda-Valbuena et al. (2022) found that treating certain proteins with pepsin reduces their allergenicity, making this treatment suitable for producing collagen hydrolysates or peptides [67].To obtain collagen hydrolysates, the collagen macromolecules need to be broken down further through processes like basic, acidic, or enzymatic hydrolysis [67].Asaduzzaman et al. (2020) demonstrated that acidic or basic conditions, along with subcritical water hydrolysis (which avoids toxic solvents and collagen degradation), are preferable for collagen degradation [68].Pepsin treatments for collagen extraction have been reported by Asaduzzaman et al. (2020) for collagen from mackerel bones (Scomber japonicus) and skin, as well as by Zhang et al. (2017) for frog skin (Rana nigromaculata) using a 0.5 M acetic acid extract containing 0.1% pepsin for 72 h [68,69].

Procedures Applied to the Isolation of Collagen from Invertebrates
In the case of other invertebrate marine organisms, it has been necessary to resort to adapted procedures for collagen extraction.For example, jellyfish collagen is generally precipitated with an aqueous solution of 2.3-2.6 M NaCl.
The collagen precipitate is collected, centrifuged, and solubilized in a 0.5 M acetic acid solution (about three days), followed by salting by dialysis with a NaHPO4 solution.The precipitated collagen is separated by centrifugation, then solubilized in acetic acid and purified by reprecipitation with the addition of solid NaCl to a concentration of 0.9 M. Acid-soluble collagen (ASC) can be digested with pepsin to obtain atelocollagen [19].In the case of sea urchins, the intact collagen fibrils in the peristomal membranes are different from other types of collagen and cannot be extracted by traditional acid solubilization methods, as this method generally produces it as hydrolyzed gelatin.The shredded native tissue is sequentially treated with a hypotonic solution and a specific decellularization solution to remove both cellular debris and skeletal parts and pigments.After 3-4 days in the β-mercaptoethanol disaggregating solution, collagen fibers are obtained, which are then passed through a filtration step and dialyzed in a 0.5 M EDTA-Na solution [19].The same protocol is employed for extracting collagen fibers from the aboral arm walls of the starfish.However, an additional step is introduced wherein the samples undergo treatment with 1 mM citric acid between the decellularization and disaggregation solutions.This step is crucial for eliminating calcium carbonate osmosis present in the fresh tissue [19].In a study conducted by Sun et al. (2021), soluble collagen (ASC), pepsin-soluble collagen (PSC), and water-soluble gelatin (WSG) were extracted from squid (Dosidicus gigas) skin.They found that using the ASC process at 4 • C resulted in the lowest yield of 33.5% [70].The addition of pepsin (PSC process) increased the collagen yield by approximately 35.0%.The highest yield of 81.9% was achieved through water extraction at 60 • C (WSG).The authors demonstrated that low temperatures can effectively preserve the native helix structures of ASC and PSC.In contrast, heat treatment led to the transformation of collagen into gelatin with uncoordinated and denatured structures [70].Antioxidant peptides derived from marine fish are obtained by enzymatic hydrolysis methods using different types of enzymes (alkalase, α-chymotrypsin, neutrase, papain, pepsin, and trypsin).Castaneda-Valbuena et al. (2022) showed that the use of optimized buffer systems is required for these enzymes [67].Separation of peptides is carried out by using chromatographic techniques and ultrafiltration membranes.After collecting the peptide fractions, the lyophilization step follows to obtain purified peptides [67].
Figure 2 illustrates the commonly employed methods for extracting marine collagen from fish.These include the following: (A) acid treatment, (B) enzymatic treatment, and (C) extraction using pepsins for marine collagen [65].Additionally, Figure 2 outlines the general procedures for generating collagen peptides from fish skin and bones [65].

Ultrasonic Procedure
The ultrasonic protein extraction process is simple, fast, risk-free, reliable, and financially beneficial.Ultrasonication leads to increased enzyme activity and helps remove temperature-sensitive chemicals.Shaik et al. (2021) studied the effect of ultrasound on collagen extraction in ASC and PSC procedures and showed that the method, being noninvasive, can obtain collagen with an almost intact structure [59].However, prolonged exposure to ultrasound can lead to a cavitational effect, resulting in elevated temperatures, shear forces, and pressures within the medium.This effect causes the disruption of hydrogen bonds and van der Waals interactions in polypeptide chains, ultimately leading to protein denaturation.Despite these drawbacks, studies such as Shaik

Ultrasonic Procedure
The ultrasonic protein extraction process is simple, fast, risk-free, reliable, and financially beneficial.Ultrasonication leads to increased enzyme activity and helps remove temperature-sensitive chemicals.Shaik et al. (2021) studied the effect of ultrasound on collagen extraction in ASC and PSC procedures and showed that the method, being non-invasive, can obtain collagen with an almost intact structure [59].However, prolonged exposure to ultrasound can lead to a cavitational effect, resulting in elevated temperatures, shear forces, and pressures within the medium.This effect causes the disruption of hydrogen bonds and van der Waals interactions in polypeptide chains, ultimately leading to protein denaturation.Despite these drawbacks, studies such as Shaik

Other Methods
There are alternative methods for extracting collagen from marine resources; however, they are not as popular as ASC, PSC, and ultrasonic treatments [52].Figure 3 shows the marine collagen extraction procedures with their advantages and disadvantages.
The WSC procedure has been used to extract collagen from marine invertebrates [70].This water-soluble collagen (WSC) is produced at 60 • C and is relatively easy to make.However, the process ultimately transforms the collagen into gelatin with uncoordinated and denatured structures, as demonstrated by Sun et al. (2021) [70].
The subcritical water hydrolysis (SBW) procedure represents a green alternative to traditional methods.It involves using water at temperatures between 150 and 300 • C and pressures between 50 and 100 bar.Kıyak et al. (2024) demonstrated that this method has been successfully used for extracting collagen from various fish species and fish byproducts [52].However, a disadvantage of SBW is that the high temperatures may affect the collagen structure [52].
Antioxidants 2024, 13, x FOR PEER REVIEW 7 of 47 shows the marine collagen extraction procedures with their advantages and disadvantages.The WSC procedure has been used to extract collagen from marine invertebrates [70].This water-soluble collagen (WSC) is produced at 60°C and is relatively easy to make.However, the process ultimately transforms the collagen into gelatin with uncoordinated and denatured structures, as demonstrated by Sun et al. (2021) [70].
The subcritical water hydrolysis (SBW) procedure represents a green alternative to traditional methods.It involves using water at temperatures between 150 and 300 °C and pressures between 50 and 100 bar.Kıyak et al. (2024) demonstrated that this method has been successfully used for extracting collagen from various fish species and fish byproducts [52].However, a disadvantage of SBW is that the high temperatures may affect the collagen structure [52].
The supercritical fluid extraction (SFE) procedure is an alternative to traditional extraction methods.SFE uses a supercritical fluid, typically CO2, as the extracting solvent to separate components.CO2 is preferred due to its numerous advantages.The primary benefit of SFE is the ability to obtain purified components.Marine fish belong to the vertebrate category, and the raw materials used to isolate collagen from fish are skin, bones, scales, cartilage, and other by-products (such as swimming fins).Fish by-products can vary in composition depending on the size of the fish, the species, and the technology used to process them.Type I collagen obtained from these by-products is preferred.Among the research carried out for the extraction of collagen from skin fish, we list the isolation collagen from Alu-Alu (Sphyraena sp.) by Matarsim et al. (2023) [75].The extraction of collagen from skins of Asian sea bass and Spanish mackerel (Scomberomorus commerson) was performed by Ampitiya et al. (2023) [47].Collagen and collagen peptide excision from the skin of round goby fish (Neogobius melanostomus) by Yemisken et al. (2023) and from the skin of silver catfish (Pangasius sp.) by Shaik et al. (2023) have been reported [76,77].Type I collagen was extracted from other The supercritical fluid extraction (SFE) procedure is an alternative to traditional extraction methods.SFE uses a supercritical fluid, typically CO 2 , as the extracting solvent to separate components.CO 2 is preferred due to its numerous advantages.The primary benefit of SFE is the ability to obtain purified components.Marine fish belong to the vertebrate category, and the raw materials used to isolate collagen from fish are skin, bones, scales, cartilage, and other by-products (such as swimming fins).Fish by-products can vary in composition depending on the size of the fish, the species, and the technology used to process them.Type I collagen obtained from these by-products is preferred.Among the research carried out for the extraction of collagen from skin fish, we list the isolation collagen from Alu-Alu (Sphyraena sp.) by Matarsim et al. (2023) [75].The extraction of collagen from skins of Asian sea bass and Spanish mackerel (Scomberomorus commerson) was performed by Ampitiya et al. (2023) [47].Collagen and collagen peptide excision from the skin of round goby fish (Neogobius melanostomus) by Yemisken et al. (2023) and from the skin of silver catfish (Pangasius sp.) by Shaik et al. (2023) have been reported [76,77].Type I collagen was extracted from other fish by-products, such as unicornfish (Naso reticulatus) bones obtained by Fatiroi et al. (2023) [78].Research has been reported to isolate collagen from parrotfish (Scarus sordidus) scales by Jaziri et al.  [81][82][83].Research on the extraction of marine collagen from different fish by-products was reported, including from the bones of lizardfish (Saurida tumbil) by Jaziri et al. (2022), and from the tail tendon of skipjack tuna (Katsuwonus pelamis) by Chanmangkang et al. (2022) [84,85].Marine collagen was isolated from the swim bladder of grass carp (Ctenopharyngodon idella) by Dong et al. (2022), and from the skin of Greenland halibut (Reinhardtius hippoglossoides) by Martins et al. (2022) [86,87].Other research to obtain marine collagen was done from catfish (Silurus triostegus) skin by Abbas et al. (2022) and from dusky grouper (Epinephelus marginatus) scales by Tziveleka et al. (2022) [88,89].Collagen was isolated from shark (Prionace glauca) cartilage by Seixas et al. (2020) and from surgeon fish (Huso huso) skin by Atef et al. (2020) [62,90].Zhang et al. (2022) reported data on gelatin from the cartilage of Siberian sturgeons (Acipenser baerii) [91].Type I collagen was extracted from the swim bladder of giant croakers (Nibea japonica) by Chen et al. (2019) and from the skin of bigeye tuna (Thunnus obesus) by Ahmed et al. (2019) [92,93].Kittiphattanabawon et al. (2019) also extracted collagen from Nile tilapia (Oreochromis Niloticus) scales by ASC and PSC procedures [94].Studies for the extraction of marine collagen from the skin of silver catfish (Chrysichthys nigrodigitatus) were reported by Hukmi et al. (2018) [95].Iskandar et al. (2018) extracted collagen from the skin of bonylip barb fish (Osteochilus vittatus) [96].Changfeng C. et al. (2013) characterized collagens from the cartilage of the Scottish hammerhead (Sphyrna lewini), and Zhong-Rui reported data on collagens from the skin and bone of the Spanish mackerel (Scomberomorous niphonius), [97,98].Hu et al. (2023) reported data on the utilization of peptides from the collagens of monkfish (Lophius litulon) swim bladders [99].Li et al. (2018) reported studies obtaining collagen from scales of the Miiuy croaker (Miichthys miiuy) [100].Other studies on the isolation and valorization of collagen from fish and fish derivatives were reported.Nurmila et al. conducted research on the extraction and characterization of antioxidant activities from yellowfin tuna Thunnus albacares skin [101,102].Studies concerning collagen from skin of grey mullets from the Black Sea were also reported by Cherim et al. in 2019 andin 2017 [103,104].Collagen extracted from the skin of bluefin tuna (Thunnus orientalis) was reported by Tanaka et al. (2018) [63].

Collagen from Marine Invertebrates
Collagen isolation from invertebrates has been relatively less studied.Sea sponges, sponges or poriferans are part of a category of invertebrates that have been shown to be a potential source of collagen, although they have been little investigated.To date, about 8500 species are known.The class Demospogiae includes Chondrosia reniformis, which has been studied as a potential collagen source by Tassara 2021) reported studies on the biological performance of marine sponge collagen [108].Parisi et al. (2019) reported on the biological activities of materials derived from spongin, a form of collagen from marine sponges, when incorporated into other materials [109].Langasco et al. (2017) explored the use and enhancement of the natural collagen-horny skeleton of marine sponges (Porifera, Dictyoceratida) as a biologically based dressing for topical drug delivery [110].
Table 1 shows recent studies with data on the part of the body analyzed, the type of extraction method, the yield obtained for collagen, data on collagen analysis methods for identification, and the type of collagen identified.In addition to marine sponges, echinoderms of the phylum Echinodermata, which includes five distinct classes, were also studied for their collagen.Vate et al. (2023) investigated collagen in the common starfish (Asterias rubens), while Han et al. (2021) studied collagen in the starfish (Asterias pectinifera) [111,112].Li et al. (2020) extracted a high percentage of collagen, up to 72%, from the sea cucumber Holothuria cinerascens, demonstrating its potential as a marine collagen resource [113].Tian et al. (2020) also extracted collagen from the sea cucumber Apostichopus japonicus [114].Another promising source of marine collagen is the Coelenterates.Esparza-Espinoza et al.'s (2019) remarkable research involved extracting collagen from the jellyfish Stomolophus meleagris [115].Additional studies include those conducted by Felician et [80,82,113].

Structural Characteristics of Collagen and Collagen Peptides
Collagen is a protein found in all living things.This protein has a complex structure consisting of 29 collagen types, as explained by Cherim et al. (2019) and Meyer et al. (2019) [42,125].In vertebrates, type I collagen is the most abundant type in the body and can be found in bones, skin, tendons, and organs, as explained by Meyer et al. (2019) [125].Type II collagen is found in cartilage.Type III collagen is present in reticular fibers as well as in blood and skin [125].In invertebrates, type I and IV collagens are found.By partial denaturation of native collagen, gelatin is obtained, which is a major source of protein biopolymers.Collagen peptides are fragments of collagen with lower molecular masses that are detached from the large triple helix chain.Ryu et al. (2021) showed that proteolytic enzymes can break down proteins into hydrolysates comprising small peptides consisting of 2-20 amino acids [126].
The molecular weight, length, and sequence of peptides, as well as their amino acid composition, influence their bioactive properties; hydrolysates produce amino acid forms that are useful in supporting various human biological functions, as stated by Yathisha 2022) analyzed the differences generated by the structure of three commercial tuna species with modern methods of analysis [131,132].Hernández-Ruiz et al. (2023) analyzed the structure of collagen peptide fractions from tilapia (Oreochromis aureus Steindachner, 1864) scales [133].Figure 4 shows the structure of collagen, collagen peptides, and amino acid chains [34].Also highlighted are the top five collagen types and the locations where they are most abundant.

Amino Acids in Marine Collagen
In vertebrates, different types of collagen show tropocollagen structures.These molecules consist of approximately 35% glycine (Gly), 21% proline (Pro), 11% alanine (Ala), and hydroxyproline (Hyp) [126].Hydroxyproline at the Y-position is believed to enhance the stability of the helical structure.From a nutritional perspective, amino acids are categorized as essential (EAA), non-essential (NEAA), or conditionally essential (CEAA).The concept of functional amino acids (FAA) has also been introduced; these amino acids are involved in and regulate metabolic pathways that improve health, growth, development, survival, reproduction, neurological metabolic diseases, and infectious diseases [126].
Arg, His, Cys, Lys, Leu, Thr, Met, Trp, Tyr, and Val are EAA; Pro, Glu, Gln, and Gly are CEAA; and Ala, Ser, and Asp are NEAA for human nutrition.In human nutrition, Arg, Cys, Leu, Met, Trp, Tyr, Asp, Glu, Gly, and Pro have been classified as FAA, as shown by Šimat et al. (2020) [7]. Figure 5 shows the potential marine sources of essential amino acids (EAA).

Amino Acids in Marine Collagen
In vertebrates, different types of collagen show tropocollagen structures.These molecules consist of approximately 35% glycine (Gly), 21% proline (Pro), 11% alanine (Ala), and hydroxyproline (Hyp) [126].Hydroxyproline at the Y-position is believed to enhance the stability of the helical structure.From a nutritional perspective, amino acids are categorized as essential (EAA), non-essential (NEAA), or conditionally essential (CEAA).The concept of functional amino acids (FAA) has also been introduced; these amino acids are involved in and regulate metabolic pathways that improve health, growth, development, survival, reproduction, neurological metabolic diseases, and infectious diseases [126].
Arg, His, Cys, Lys, Leu, Thr, Met, Trp, Tyr, and Val are EAA; Pro, Glu, Gln, and Gly are CEAA; and Ala, Ser, and Asp are NEAA for human nutrition.In human nutrition, Arg, Cys, Leu, Met, Trp, Tyr, Asp, Glu, Gly, and Pro have been classified as FAA, as shown by Šimat et al. (2020) [7]. Figure 5 shows the potential marine sources of essential amino acids (EAA).

Amino Acids in Marine Collagen
In vertebrates, different types of collagen show tropocollagen structures.These molecules consist of approximately 35% glycine (Gly), 21% proline (Pro), 11% alanine (Ala), and hydroxyproline (Hyp) [126].Hydroxyproline at the Y-position is believed to enhance the stability of the helical structure.From a nutritional perspective, amino acids are categorized as essential (EAA), non-essential (NEAA), or conditionally essential (CEAA).The concept of functional amino acids (FAA) has also been introduced; these amino acids are involved in and regulate metabolic pathways that improve health, growth, development, survival, reproduction, neurological metabolic diseases, and infectious diseases [126].
Arg, His, Cys, Lys, Leu, Thr, Met, Trp, Tyr, and Val are EAA; Pro, Glu, Gln, and Gly are CEAA; and Ala, Ser, and Asp are NEAA for human nutrition.In human nutrition, Arg, Cys, Leu, Met, Trp, Tyr, Asp, Glu, Gly, and Pro have been classified as FAA, as shown by Šimat et al. (2020) [7]. Figure 5 shows the potential marine sources of essential amino acids (EAA).

Amino Acids from Fish Collagen
The amino acid content of collagen in fish is very different depending on the species of fish, the marine habitat in which it lives, and the pollutants present in marine waters, especially in coastal waters.Research reported on the amino acid content of marine collagen extracted from fish skin and fish by-products shows a different distribution of amino acid types.Blanco 2023) reported the amino acid composition of collagen extracted from the fish Totoaba macdonaldi, with the highest values for Gly, Ala, Pro, and Glu [81].From the presented analysis, we can see that the main amino acids in most of the collagens in pest skin are Gly, Pro, Ala, Glu, Hyp, and Val.The amino acid Ala, although belonging to the category of non-essential amino acids, is quantitatively found in all collagen extracts from the skin of the marine fish studied.Pro and Ala were the most abundant hydrophobic amino acids in all fish species.It was concluded that hydrophobic amino acids were observed in several peptide sequences with antioxidant properties.Akita et al. (2020) reported studies on the correlation between the content of Pro, Hyp, and Ser and the denaturation temperature of type I collagen with the physiological temperature of marine organisms [141].The degree of hydroxylation of Pro and Lys is known to influence the thermal stability of collagen [141].Chinh et al. (2019) reported amino acid sequences of Carp fish scale wastes [142].From the presented analysis, we can see that the main amino acids in most of the collagens in fish skin are Gly, Pro, Ala, Glu, Hyp, and Val.Pro and Ala were the most abundant hydrophobic amino acids in all fish species, although there were clear differences.Tryptophan (Trp) was not found in all of the species.Table 2 shows the experimental results for the amino acid content of collagen hydrolysates extracted from the skin or swim bladder of the different fish species presented.Regardless of the units of measurement used for reporting these amino acids, Gly consistently appears in the highest amounts across all species analyzed.The values are typically expressed in residues per 1000 residues.

Amino Acids from Crustacean Collagen
Gly is found to be the amino acid found in all species studied except Rhizostoma pulmo, studied by Cheng et 2023) reported that amino acids were also found in Rhizostoma pulmo in the order Gly, Glu, Ala, Asp, and Leu [147].Table 3 shows the results of amino acids found in collagen extracts from marine invertebrates: different species of jellyfish, mollusks, and one species of shrimp.Amino acid values are generally reported in mass percent.2021) reported the amino acid content of the white shrimp Litopenaeus vannamei with higher values for Gly, Arg, Pro, and Ala.It does not show hydroxylysine (Hyl) [151].The amino acid content of mollusk and shrimp species is much lower than that of jellyfish species.Lima et al. (2019) found that amino acids such as Asp, Gly, and Glu improve wound healing [152].Hydrophobic amino acids have antioxidant action as they can interact on membrane lipid layers to reach targets and help scavenge radicals [149,152].

Antioxidant Activity
Oxidation is a vital and normal process in vertebrates and humans, whereby free radical species (ROS) are continuously generated in the cellular metabolism.The accumulation of ROS in the body must be kept under control to avoid the diseases they can cause.Oxidative stress is linked to damaging processes such as lipid peroxidation, protein damage, DNA breakdown, or enzyme inactivation.These promote the development of various diseases such as tumor formation or cancer, heart disease, rheumatoid arthritis, or aging.Suo et al. (2022) showed that seventeen ACE inhibitory peptides isolated from the protein hydrolysate of the blue mussel Mytilus eludis could be used as natural ingredients in the development of products with antihypertensive functions [153].Hydrolysates and collagen peptides from fish by-products have demonstrated antioxidant capacity to reduce oxidative processes and can thus be used to produce functional foods.There were researchers like Nikoo et al. (2021) and Nirmal et al. (2022) who reported that certain hydrophobic amino acid sequences provide antioxidant properties as proton or electron donors or as lipid radical scavengers [154,155].The antioxidant properties of marine collagen peptides and hydrolysates are influenced by several parameters, such as amino acid composition, chain size and length, or residue/chain sequence [150,154].Chaoting et al. (2020) emphasized the relationship between peptide structure and the antioxidant activity of peptides isolated from proteins [156].The relationship between structure and the antioxidant activity of peptides derived from marine by-products was presented by Sila   By analyzing and summarizing the data presented in Table 4, we can see that the antioxidant activity of collagen and marine collagen were tested by different methods.The DPPH radical-scavenging activity assay method was used to reveal the antioxidant potential in all of the species exemplified in Table 4 [68,147,160,[162][163][164][165][166][167][168][169][170][171][172][173][174][175][176].The antioxidant activity with the highest percentages obtained by DPPH assay were reported by Zamorano-Apodaca et al. ( 2020), who extracted peptide fractions from mixed by-product: skins, heads, and skeletons from different fish species (different sharks, mullet, guitarfish, ray, weakfish, snapper, squid, seabass, pompano dolphinfish) [167].The authors showed that the percentages ranged from 67% to 77% at concentrations of 10 mg/m [167].Antioxidant activity reported by IC50 values that recorded the highest values (IC50 = 8.38 mg/mL) was demonstrated by Asaduzzaman et al. ( 2020), who performed DPPH assays on amino acids extracted from the bone and skin of the mackerel Scomber japonicas [68].For the other species of marine organisms reported in Table 4, the antioxidant potential was also reported by various other specific tests.ABTS scavenging activity is a widely used method for demonstrating the antioxidant activity of extracted collagen peptides [68,160,163,165,[168][169][170][171][172]175,176].The highest values by ABTS assay (83.5% at 2.5 mg/mL) were reported on collagenic peptides extracted from Cynoscion guatucupa-stripped weakfish skin-by Lima et al. (2019) [170].Appreciable values by ABTS assay (81.05% at 500 µg/mL) were also reported by Yang et al. (2020), who analyzed amino acid sequences (Ala-Thr-Val-Tyr) with antioxidant potential from the silky shark Carcharhinus falciformis [168].Another method for testing antioxidant potential was hydroxyl radical-scavenging activity [161,164,167,[169][170][171]173,176].By the hydroxyl radical-scavenging method, Zamorano-Apodaca et al. (2020) also reported the highest percentages (from 64% to 85% at concentrations of 10 mg/m) attesting to the antioxidant activity of peptide fractions extracted from mixed by-products: skins, heads, and skeletons from different fish species (different sharks, mullet, guitarfish, ray, weakfish, snapper, squid, seabass, pompano dolphinfish) [167].The superoxide anion radical-scavenging method was also used to reveal antioxidant activity [161,169,171,172,176].Using superoxide anion radicalscavenging method on invertebrates, the highest values expressed by IC50 ( IC50 = 1.55 mg/mL) for collagen from whole tissue in the jellyfish Nemopilema nomurai were reported by Teng et al. (2023), and in vertebrates the highest values (IC50 = 0.91 mg/mL) were reported by Zhang et al. (2019) for the amino acid sequences Pro-Phe-Gly-Pro-Asp from the skin of Japanese Spanish mackerel (Scomberomorus niphonius) [161,169].FRAP ability is a method successfully used in testing the antioxidant potential for collagen compounds in both vertebrates and invertebrates [162,163,[165][166][167]175].The highest values for the antioxidant activity by the FRAP method (1.4% at 2 mg/mL) were reported by Ahmed et al. (2022) for C-and N-terminal amino acid sequences from Pampus argenteus skins [162].Table 4 presents the results of antioxidant activity studies conducted by various researchers on different marine species.By analyzing and summarizing the data presented in Table 4, we can see that the antioxidant activity of collagen and marine collagen were tested by different methods.The DPPH radical-scavenging activity assay method was used to reveal the antioxidant potential in all of the species exemplified in Table 4 [68,147,160,[162][163][164][165][166][167][168][169][170][171][172][173][174][175][176].The antioxidant activity with the highest percentages obtained by DPPH assay were reported by Zamorano-Apodaca et al. ( 2020), who extracted peptide fractions from mixed by-product: skins, heads, and skeletons from different fish species (different sharks, mullet, guitarfish, ray, weakfish, snapper, squid, seabass, pompano dolphinfish) [167].The authors showed that the percentages ranged from 67% to 77% at concentrations of 10 mg/m [167].Antioxidant activity reported by IC 50 values that recorded the highest values (IC 50 = 8.38 mg/mL) was demonstrated by Asaduzzaman et al. ( 2020), who performed DPPH assays on amino acids extracted from the bone and skin of the mackerel Scomber japonicas [68].For the other species of marine organisms reported in Table 4, the antioxidant potential was also reported by various other specific tests.ABTS scavenging activity is a widely used method for demonstrating the antioxidant activity of extracted collagen peptides [68,160,163,165,[168][169][170][171][172]175,176].The highest values by ABTS assay (83.5% at 2.5 mg/mL) were reported on collagenic peptides extracted from Cynoscion guatucupa-stripped weakfish skin-by Lima et al. (2019) [170].Appreciable values by ABTS assay (81.05% at 500 µg/mL) were also reported by Yang et al. (2020), who analyzed amino acid sequences (Ala-Thr-Val-Tyr) with antioxidant potential from the silky shark Carcharhinus falciformis [168].Another method for testing antioxidant potential was hydroxyl radical-scavenging activity [161,164,167,[169][170][171]173,176].By the hydroxyl radical-scavenging method, Zamorano-Apodaca et al. (2020) also reported the highest percentages (from 64% to 85% at concentrations of 10 mg/m) attesting to the antioxidant activity of peptide fractions extracted from mixed by-products: skins, heads, and skeletons from different fish species (different sharks, mullet, guitarfish, ray, weakfish, snapper, squid, seabass, pompano dolphinfish) [167].The superoxide anion radical-scavenging method was also used to reveal antioxidant activity [161,169,171,172,176].Using superoxide anion radical-scavenging method on invertebrates, the highest values expressed by IC 50 (IC 50 = 1.55 mg/mL) for collagen from whole tissue in the jellyfish Nemopilema nomurai were reported by Teng et al. (2023), and in vertebrates the highest values (IC 50 = 0.91 mg/mL) were reported by Zhang et al. (2019) for the amino acid sequences Pro-Phe-Gly-Pro-Asp from the skin of Japanese Spanish mackerel (Scomberomorus niphonius) [161,169].FRAP ability is a method successfully used in testing the antioxidant potential for collagen compounds in both vertebrates and invertebrates [162,163,[165][166][167]175].The highest values for the antioxidant activity by the FRAP method (1.4% at 2 mg/mL) were reported by Ahmed et al. (2022) for C-and N-terminal amino acid sequences from Pampus argenteus skins [162].Table 4 presents the results of antioxidant activity studies conducted by various researchers on different marine species.Antioxidant activity can also be assessed by metal-chelating activity [68,165,166].The highest values in the metal-chelating method were reported by Khesal et al. (2020) for peptide fractions from by-products from Rutilus frisii kutum [166].To attest antioxidant activity, some authors have used four different types of methods; for example, Chotphruethipong et al. (2021) tested the antioxidant activity of hydrolyzed collagen from defatted Asian sea bass skin by four methods: DPPH, ABTS, FRAP, and the metal-chelating method [165].The highest values in the metal-chelating method were reported by Khesal et al. (2020) for peptide fractions from by-products from Rutilus frisii kutum [166].Using the DPPH, ABTS, and hydroxyl and superoxide anion radical-scavenging methods, Zhang et al. (2019) tested the antioxidant potential of amino acid sequences from mackerel (Scomberomorus niphonius) skin, and Tao et al. ( 2018) demonstrated the antioxidant activity of amino acid sequences from Mustelus griseus cartilage [169,171].Also, Yang et al. (2019) reported the antioxidant potential of amino acid sequences from the mollusk Tergillarca granosa by four methods: DPPH, ABTS, and the hydroxyl and superoxide anion radical-scavenging methods [176].Note from Table 4 that antioxidant activity was only reported by DPPH assay for the collagen extracted from the jellyfish Lobonema smithii and Rhopilema hispidum by Muangrod et al. (2022), and the values for collagen extracted from oral arms are higher than those from whole tissue and respective umbrellas in both jellyfish species [174].Also, by a single method, ABTS, the antioxidant activity of the peptide fraction < 3 kDa from Pangasius hypopthalmus skin was reported by Azizah et al. [160].Also, Yang et al. (2019) reported the antioxidant potential of amino acid sequences from the mollusk Tergillarca granosa by four methods: DPPH, ABTS, and the hydroxyl and superoxide anion-scavenging method [176].
The antioxidant activity is attributed to the amino acid sequences in collagen peptides and varies based on the type of enzymatic hydrolysate used for their separation, as shown in Table 5. Zhao et al. (2018) investigated collagen peptides with antioxidant potential by using pepsin for enzymatic hydrolysis [66].They isolated collagen from the swim bladders of the Miiuy croaker (Miichthys miiuy).Dong et al. ( 2022) also used pepsin to isolate collagen from the swim bladders of several fish species, including Miichthys miiuy, Labeo rohita, Thunnus albacares, and Silurus triostegus [86].Zhang et al. (2019) identified amino acid sequences from the skin of Lophius litulon, reporting antioxidant activity tested by various specific methods [169].
The antioxidant activity of collagen peptides has also been reported in invertebrates, particularly jellyfish.2022); it showed antioxidant activity tested by specific methods, DPPH, superoxide anion radical scavenging, FRAC ability, TEAC, and ORAC [101,[185][186][187]. Table 5 shows the various types of enzymes used in enzymatic hydrolysis and the antioxidant potential of collagen extracts.

Fish gutted, skinless fillets
The resulting peptide fractions exhibited high contents of amino acids Enzymatic hydrolysis with trypsin, pepsin, chymotrypsin, and visceral enzymes The highest copper-chelating activity, the highest iron-chelating activity, and β-carotene bleaching [198] Miichthys miiuy
Alkalase hydrolysis has been used to obtain collagen extracts by Viji et al. (2019), who demonstrated the antioxidant activity of collagen peptides from the skin and scales of Cynoglosus arel, and by Sae-leaw et al. (2018), who extracted such collagen with antioxidant properties from salmon scales, with antioxidant activity tested by DPPH, ABTS, and FRAP ability [188,189].
By enzymatic hydrolysis with papain, collagen was extracted and amino acid fractions with antioxidant properties were studied by Muangrod 2019) extracted collagen peptides from skipjack tuna (Katsuwonus pelamis) scales and conducted studies for the antioxidant potential attested by different methods [193][194][195].Table 5 presents studies in which the authors present the antioxidant potential of collagen extracts from brown resources attested by different specific methods but emphasize the collagen extraction methods, which, as demonstrated, can influence the extraction yield, the type and purity of extracted components, and the antioxidant properties.We find that most extraction techniques were enzymatic hydrolysis, but also other techniques.Using several types of enzymatic hydrolysis with trypsin, neutrase, protamex, flavorzyme enzymes, trypsin, bromelain, papain, pepsin, and alkalase, different collagen peptides were extracted for which the antioxidant potential was studied.Such were the studies performed by Teng 2020) for collagen peptides from the scales of red lip Croaker (Pseudosciaena polyactis), who also tested antioxidant activity [161,[194][195][196][197]. Other studies for antioxidant activity using enzymatic hydrolysis with multiple enzymes for the extraction of collagen were those reported by Qiu et al. (219) for different collagen peptides extracted from skipjack tuna (Katsuwonus pelamis) scales, and by Chel-Guerrero et al. (2020) for peptide fractions extracted from red lionfish (Pterois volitans L.), who tested the antioxidant potential using different methods [195,198].Antioxidant activity was also reported by Jin (2019) for collagen from the sea cucumber Acaudina molpadioides and by Zhao et al. (2018) for collagen peptides from the Miichthys miiuy croaker (Miichthys miiuy), both studies folding multiple enzymes to obtain collagen compounds [190,199].
Devita et al. (2021) identified amino acids from Thunnus obessus skin in different enzymatic hydrolyses (with bromelain, papain, pepsin, and trypsin), and Li et al. (2021) reported mottled duck cartilage collagen in several types of hydrolysis (enzymatic hydrolysis with trypsin, chymotrypsin, and papain) and showed the antioxidant activity of the obtained extracts by DPPH, reducing power, and ABTS [200,201].Sripokara, P. et al., (2019) using enzymatic hydrolysis with trypsin, reported the antioxidant properties of collagen peptides from starry triggerfish (Abalistes stellaris) through several assays: ABTS and DPPH, FRAP ability, and the metal-chelating activity of the hydrolysate sample, which were dose-dependent [202].
Neutrase enzymatic hydrolysis has been used by Bordbar et al. (2021), who extracted collagen from the sea cucumber Acaudina Molpadioides; by Qiu et al. (2019), who extracted gelatine and collagen peptides from skipjack tuna (Katsuwonus pelamis) scales; and by Zheng et al. (2020), who extracted collagen peptides from the swim bladders of the giant croaker (Nibea japonica) and demonstrated their antioxidant activity by different methods, specifically DPPH and ABTS, but also other specific methods [194,195,203].Using protease enzymatic hydrolysis, Baehaki et 2017) extracted two novel peptides from the head, scales, skin, and blood of sardines (Sardine (Sardina pilchardus), which they tested for their antioxidant activity by specific methods: DPPH, ABTS, and FRAP ability [204][205][206][207].
Using solvents such as diethyl ether extracts to obtain collagens from the skin of the fish Conger myriaster and Anguilla japonica, Santhanam et al. (2022) were able to isolate collagen peptides with antioxidant activity tested by DPPH assay [208].Jantaratch et al. (2022) reported amino acid fractions from the skin of Oreochromis niloticus in crude enzyme solutions from Tuna stomachs, in which they tested antioxidant activity by ABTS and FRAP [209].Rashid et al. (2023) obtained fish protein hydrolysates from Malaysian fish salami (Keropok Lekor) using enzymatic methods by Lactobacillus casei fermentation and evaluated their antioxidant and antibacterial activity [210].Dara et al. (2020) utilized hydrolysis with visceral proteases extracted from the gastrointestinal tracts of fish and demonstrated the antioxidant activity of peptide fractions obtained from Johnius dusumieris skin using DPPH, ABTS, and FRAP assays [211].
One other extraction method, hydrolysis of subcritical water for the production of bioactive peptides with antioxidant properties, has been used by Bashir et al. (2020), who identified antioxidant peptides from the mackerel (Scomber Japonicus), and by Ahmed et al. (2018), who identified bioactive peptides from tuna skin collagen [38,212].Franco et al. (2020) explored the antioxidant properties of collagen with a specific method: DPPH, ABTS, and FRAP assays for collagen extracted from sea bream and sea bass by-products utilized solvents in pulsed electric fields [213].Yanshole et al. (2019) reported interesting studies on the presence of ovothiol A (OSH) in the lenses of Sander lucioperca and Rutilus rutilus lacustris fish [214].Their study shows that high concentrations of OSH levels in fish are seasonally variable [214].

Antioxidant Applications of Nutraceuticals Based on Collagen, Gelatin, and Collagen Peptides
Nutraceuticals are specialized products consumed with food to provide health benefits beyond basic nutrition.These products come in various forms, like tablets, capsules, powders, and beverages.Functional proteins, a subset of nutraceuticals, are complex mixtures of biologically active proteins that support normal immune function.With a global shift towards healthier lifestyles, there has been a significant investment in nutritional products [215].According to global reports, the functional protein market is expected to reach USD 7.98 billion by 2026, growing at a CAGR of 6.93% from 2019 [216].
Collagen hydrolysates and peptides derived from marine sources are notable nutraceuticals due to their biological activities.

Anti-Cancer Activity
Antitumor and antioxidant activity were reported by Mizarpour et al. (2020) on studies done with hydrolysates from Barred mackerel skin, which were screened for cytotoxic activity against human MCF-7 cell line cells [217].Nine fractions obtained by hydrolysis of fish gelatin were tested, of which the F1 fraction was found to have very good antioxidant and anti-carcinogenic activities [217].Yaghoubzadeh et al. (2019) reported research on hydrolyzed proteins and collagen peptide fractions with molecular masses less than 3 kDa obtained from Rainbow trout fish, in which they evidenced antioxidant and anticancer activities in human colorectal carcinoma HCT-16 [218].Lu et al. (2017) reported the activity of two peptides extracted from cod fish skin that had essential actions in various invasive processes, inhibiting MMP-1, p-ERK, and p-p38 [219].Ramesh et al. (2021) identified the antitumor cytotoxic activity of Leji-malides (A-D), which are unique 24-membered polyene macrolides found in the species Eudistoma cf.rigida [220].Meanwhile, Ganesan et al. (2020) and Hu et al. (2012) reported both in vitro and in vivo antitumor activity on HELA and HT-29 cell lines, along with the antioxidant activity of polypeptides with a molecular weight of 20,419 Da extracted from the bivalve mollusca Archa subcrenata [215,221].Their findings showed that the tumor growth inhibition rates of P2 were 26.4%, 41.4%, and 46.4% for hepatoma cells H-22 and 34.0%, 45.8%, and 60.1% for sarcoma cells in S-180 tumorbearing mice [215,221].Figure 7 illustrates the common conditions for which nutraceutical antioxidants containing collagen hydrolysates, gelatins, or collagen peptides from marine sources are recommended.
antioxidant and anticancer activities in human colorectal carcinoma HCT-16 [218].Lu et al. (2017) reported the activity of two peptides extracted from cod fish skin that had essential actions in various invasive processes, inhibiting MMP-1, p-ERK, and p-p38 [219].Ramesh et al. (2021) identified the antitumor cytotoxic activity of Leji-malides (A-D), which are unique 24-membered polyene macrolides found in the species Eudistoma cf.rigida [220].Meanwhile, Ganesan et al. (2020) and Hu et al. (2012) reported both in vitro and in vivo antitumor activity on HELA and HT-29 cell lines, along with the antioxidant activity of polypeptides with a molecular weight of 20,419 Da extracted from the bivalve mollusca Archa subcrenata [215,221].Their findings showed that the tumor growth inhibition rates of P2 were 26.4%, 41.4%, and 46.4% for hepatoma cells H-22 and 34.0%, 45.8%, and 60.1% for sarcoma cells in S-180 tumor-bearing mice [215,221].Figure 7 illustrates the common conditions for which nutraceutical antioxidants containing collagen hydrolysates, gelatins, or collagen peptides from marine sources are recommended.2013) reported antitumor activity against various cancer cell lines.They observed mortality rates of 81%, 85%, 89%, and 90% in cell lines BT549 (breast carcinoma), HCT15 (colon carcinoma), A549 (type II lung epithelial), and PC3 (prostate cancer), respectively, at a concentration of 44 mg/mL [215,222].This activity was attributed to 50 kDa fractions containing 56% of the proteins rich in the amino acids Thr, Pro, and Gly, sourced from the mussel Mitylus edulis [215,222].Additionally, Wali et al. (2019) and Ruiz-Torres et al. (2017) highlighted the specific anticancer properties of coral derivatives.These compounds exhibit anti-inflammatory, anticancer, and antioxidant activities, suggesting potential for cancer treatment [223,224].2013) reported antitumor activity against various cancer cell lines.They observed mortality rates of 81%, 85%, 89%, and 90% in cell lines BT549 (breast carcinoma), HCT15 (colon carcinoma), A549 (type II lung epithelial), and PC3 (prostate cancer), respectively, at a concentration of 44 mg/mL [215,222].This activity was attributed to 50 kDa fractions containing 56% of the proteins rich in the amino acids Thr, Pro, and Gly, sourced from the mussel Mitylus edulis [215,222].Additionally, Wali et al. (2019) and Ruiz-Torres et al. (2017) highlighted the specific anticancer properties of coral derivatives.These compounds exhibit anti-inflammatory, anticancer, and antioxidant activities, suggesting potential for cancer treatment [223,224].

Antidiabetic Activity
Xu et al. (2022) reported studies on Gly-Pro-type peptides, containing 4-9 amino acid residues, obtained by enzymatic hydrolysis of tilapia Oreocchromis niloticus skin gelatin using seven proteases: papain, bromelain, neutrase, alkalase, protamex, flavorzyme, and trypsin [225].Some proteases showed differences in peptide release, with the authors concluding that papain released strong dipeptidyl peptidase IV (DPP-IV)-inhibitory peptides to the greatest extent from Tilapia fish skin [225].Wang et al. (2015) reported studies performed on gelatin hydrolysates on different fish from both cold and warm water [226].They demonstrated that peptide fractions with MW < 1.5 kDa obtained from Halibut and Tilapia fish presented remarkable DPP-IV inhibitory activity of 38.2% and 51.9%, respectively, at a sample concentration of 1 mg solid/mL and re-performed in vivo antihyperglycemic experiments on streptozotocin-induced diabetic rats, demonstrating improved glucose tolerance.Better results were reported for the amino-acid-rich warm-water fish gelatin from Tilapia fish as a more potent antihyperglycemic agent compared to the gelatin hydrolysate from Halibut, due to its superior amino acid content [226].

Antiobesity Activity
Wang et al. (2020) reported studies on collagen peptides with molecular weights ranging from 500 to 5000 Da, extracted from an enzymatic hydrolysate of Walleye Pollock skin, that had efficient effects against obesity in mice fed a high-fat diet [227].The results show that collagen peptide extracts from Walleye pollock are a potential agent in the development of an adjuvant for the treatment of obesity and associated metabolic diseases [227].Raksha et al. (2023) reported studies of collagen peptides extracted from the jellyfish Diplulmaris antarctica that have action in preventing and treating obesity caused by a highcalorie diet and in curing other pathologies associated with increased oxidative stress [228].

Osteoarthritis and Bone Diseases
Luo et al. ( 2022) characterized low-molecular-weight collagen peptides, primarily composed of Gly, Ala, and Pro, extracted from Atlantic salmon bone.They evaluated these peptides' effects on chondrocytes induced by interleukin 1β (IL-1β) and assessed their efficacy and safety as anti-osteoarthritis agents through biomarker testing.The goal was to develop a dietary supplement that could delay arthritis development and support anti-inflammatory cartilage regeneration [229].

Cardiovascular Diseases
Hypertension has recently become a major global problem.In recent decades, there has been increasing interest in natural ACE-inhibitory peptides from food.These include by-products from fish skin: collagen, collagen hydrolysates, and collagen peptides, which are an important source of ACE-inhibitory peptides.Cui L. et al. (2023) studied antiplatelet peptides in collagen hydrolysates from silver carp skin that were enriched using macroporous resins.The results showed the yield and antiplatelet activity of the 20% ethanol fraction with an IC 50 of 2.03 mg/mL, which recommended the use of fish antiplatelet peptides as functional foods [230].
In most cardiovascular diseases, atherosclerosis occurs, which is inflammation of the blood vessels.Liu H. et al. (2022) demonstrated through research on collagen hydrolysates from Atlantic salmon fish skin (Salmo salar) that they possess potent anti-inflammatory activity, protective activity against endothelial cell injury, antioxidant activity, and antiplatelet aggregation activity in vitro [231].Also, collagen hydrolysates from Salmon fish showed combined effects on the regulation of serum biomarkers of inflammation (IL-6 and TNF-α), on endothelial injury (MCP-1), activating platelets (TXB2 and PF4), and regulating oxidative stress.It can be a dietary supplement for the prevention of atherosclerosis [231].Abdelhedi et al. (2017) conducted comparative studies on gelatin hydrolysates extracted from black-barred halfbeak (Hemiramphus far) hides using different acidic, alkaline, and enzymatic hydrolysis treatments [232].Their research demonstrated the high antioxidant potential of fish collagen hydrolysates and highlighted the ACE-inhibitory activity of peptides as a promising nutraceutical product for various cardiovascular diseases [232].
Similarly, Aissaoui et al. (2017) studied collagenous hydrolysates from scorpion fish (Scorpaena notata) red fish heads obtained through enzymatic treatments.The authors showed that these peptides exhibit high inhibitory activity against the angiotensin-Iconverting enzyme, with IC 50 values of 0.98, 1.69, and 1.44 µm.They also concluded that fish by-products can be exploited as nutraceuticals against oxidative stress and hypertension [233].2018) studied peptides extracted from the hydrolysates of jellyfish gonads (Rhopilema esculentum Kishi-nouye) using neutral proteases.These peptides with the SY amino acid sequence demonstrated both good ACE-inhibitory and antioxidant activities [237].This purified dipeptide is recommended as a functional food material for its antioxidant properties and ACE-inhibitory activity [237].

Oral Diseases
One of the most prevalent diseases of the oral cavity is oral mucosal ulcers, which manifest as severe burning pain and difficulty chewing, drinking, and even speaking.Gao et al. (2022) evidenced the role of collagens from marine resources in the healing of oral cavity wounds [244].They demonstrated that low-molecular-weight collagen peptides from Tilapia fish skin play a role in the healing of traumatic oral ulcers in rats [244].Xu et al. (2021) proved through research on periodontal membrane cell culture experiments of hydrolyzed Tilapia fish collagen that it has the function of regenerating periodontal tissue in vitro [245].Tilapia fish collagen has been used in the production of composite membranes as nanofibers, together with bioactive glass and chitosan.Zhou, T et al. (2017) made a biomimetic fish collagen/bioactive glass/chitosan (Col/BG/CS) nanofiber composite membrane to study the biological effects on human periodontal ligament cells (HPDLCs) [246].The results of Tang et al. (2015) suggested that tilapia scale collagen might be a potential alternative to type I collagen for use in oral diseases [247].Liu C et al. (2015) suggested for the first time that hydrolyzed tilapia fish collagen (HFC) can be used for periodontal tissue regeneration and is a promising bioactive ingredient for biomaterials used in alveolar bone regeneration [248].

Wound Healing Activity
Chotphruethipong et al. (2021) proved antioxidant and anti-inflammatory activities in wound healing of sea bass (Lates calcarifer) collagen hydrolysates conjugated with epigallocatechin gallate through the inhibition of nitric oxide production and tumor necrosis factor-α in RAW264.7 cells [192].Also, Chotphruethipong et al. in 2021 reported studies on two collagenous peptides (PO and POG) isolated from the skin of Asian sea bass (Lates calcarifer), which showed antioxidant effects [249].Sivarman et al. (2021) showed that the collagen peptide induces cell growth and migration of fibroblast cells and facilitates the wound healing process.They recommended the use of these peptides as a functional ingredient for nutraceuticals used in wound healing [250].Chen et al. (2019) demonstrated the existence of collagen peptides from a collagen sponge extracted from the bladder of Nibea japonica with the GAPO sequence, which produced accelerated wound healing [92].Mice treated with sponge collagen had significantly reduced interleukins.These have potential applications for wound healing.

Anti-Inflammatory Activity
Sivaraman et al. (2021) reported obvious anti-inflammatory effects generated by peptide fractions with molecular weights of 1-3 kDa extracted from the skin of the fish Clarias batrachus and Pangasius pangasius.Peptide fractions from these two fish species showed a suppression of inflammatory proteins (TNF-α, IL-6, NF-κB, and p-IκB).Due to these properties, the collagen hydrolysates of these fish species can be functional foods, and purified fractions can be used as nutraceuticals with anti-inflammatory properties [250].

Anti-Aging and Skin Protection Activity
Skin aging occurs under the action of intrinsic (e.g., aging) and extrinsic (e.g., smoking and UV) factors.UV irradiation consists of UV-A, UV-B, and UV-C.Fu et al. (2022) showed that UV-B radiation is responsible for the largest proportion of photoaging, mainly by inducing epidermal and superficial dermal damage [251].They demonstrated that UV-B irradiation can cause excessive production of reactive oxygen species (ROS) and a range of skin Damage through several signaling pathways, such as the stimulation of mitogen-activated protein kinase (MAPK) activity [251].Xia et al. (2021) reported on natural bioactive peptides with anti-aging effects.They detailed the molecular mechanisms involved [252].Maia Campos et al. (2021) evaluated the clinical efficacy of low-dose oral supplements of fish cartilage hydrolysate [253].After a 90-day treatment period, there was a significant reduction in wrinkles and an increase in dermis echogenicity compared to the placebo and baseline values [253].
Table 6 systematizes the biological activities of collagen hydrolysates, collagen peptides, and amino acid sequences from various marine organisms with results in the treatment of various diseases.2020) studied the by-products of Atlantic salmon (Salmo salar) and extracted enzymatic hydrolysate collagenic peptides from them [254].Their research identified six fractions, with fraction C6 demonstrating the strongest antiallergic activity [254].Additionally, they isolated a novel eleven-amino-acid peptide, TPEVHIAVDKF, which showed antiallergic properties.This study suggests that Atlantic salmon by-products could be a valuable source of new ingredients for food and pharmaceutical products aimed at managing food allergies [254].

Treating Malnutrition
Salindeho et al. ( 2022) reported studies on fish scale peptides mixed with hydroxyapatite and chitin and showed that each component has multiple beneficial properties for the human body as an antioxidant, in the treatment of malnutrition, as a hypocholesterollowering agent, and in bone metabolism [255].6.11.3.Iron Deficiency Treatment Wu et al. (2015) reported studies on Pacific cod gelatin and showed that several amino acids can be bound by iron ions.This study suggests a potential application of gelatin-derived peptides as novel carriers to combat iron deficiency [256].

Conclusions
The present study highlights the significance of marine-derived collagen compounds and marine resources for obtaining collagen and collagen peptides from both invertebrates and vertebrates.Based on the literature, enzymatic hydrolysis of collagen, which releases peptides and peptide moieties, is an efficient method for obtaining natural antioxidant compounds from marine sources.Various tests, such as DPPH and ABTS scavenging activity, hydroxyl and superoxide anion radical-scavenging activity, FRAP capacity, and metal-chelating activity, have demonstrated antioxidant activity.However, there are limited data on the beneficial effects of these isolated collagen peptide fractions on human health in in vivo studies for alternative treatments.This review has shown that marine collagen antioxidants from different vertebrate and invertebrate species can be involved in treatments for cancer, diabetes, obesity, osteoarthritis, cardiological conditions, and Alzheimer's disease.Additionally, collagen antioxidants are used in bone tissue regeneration and osteoarthritis, antihypertensive and neurodegenerative diseases, oral and dental diseases, cell regeneration against oxidative stress, skin lesion healing and protection, anti-inflammatory and anti-allergic responses, and iron deficiency treatments.
The global consumption of marine products has increased due to the use of marine by-products, which are rich in bioactive components that enhance human health by creating novel nutraceutical compounds with antioxidant properties.The objective of fully exploiting marine resources can also be achieved through the efficient and effective use of fish by-products (skin, bones, scales, fins, and fish heads) which contain significant amounts of collagen and collagen peptides.This paper supports the growing utilization of marine antioxidant biocompounds.However, it is often unclear what kind of water or cultural environment certain by-products originate from, raising concerns about the efficacy and safety of these nutraceuticals for human health.Therefore, further research is needed to identify barriers and ensure successful production of antioxidant nutraceuticals from marine resources in the food, pharmaceutical, and biomedical industries.

Figure 1 .
Figure 1.Marine sources for the preparation of marine collagen.

Figure 1 .
Figure 1.Marine sources for the preparation of marine collagen.

Figure 3 .
Figure 3. Advantages and disadvantages of marine collagen extraction procedures.

Figure 3 ,
as presented by Kıyak et al. (2024), outlines additional advantages and disadvantages of the SFE method [52].3.3.Data on the Isolation of Marine Collagen 3.3.1.Marine Collagen Isolated from Leather and Marine Fish Waste

Figure 3 .
Figure 3. Advantages and disadvantages of marine collagen extraction procedures.
et al. (2016) [157].Other researchers, such as Phadke et al. (2021) and Nirmal et al. (2023), considered that the molecular weight of peptides influences their antioxidant activity [158,159].The amino acids Tyr, Met, Hys, Lys, and Trp have strong radical-scavenging activity in oxidative reactions [158].Nirmal et al. (2023) explained that Hys significantly enhances the antioxidant capacity because protonation of the imidazole ring acts as a hydrogen donor [159].Azizah et al. (2020) showed that another factor influencing the antioxidant activity of peptides besides amino acid composition is the specificity of the protease used in the hydrolytic process [160].Nirmal et al. (2023) consider the degree of enzymatic hydrolysis important in assessing the antioxidant activity of proteins and peptide derivatives in fish [159].The types of enzymatic hydrolysis for several types of enzymes described by Teng et al. (2023) are trypsin, papain, pepsin, alcalase, flavourzyme, protamex, and bromlaine.pH values are 2.0-9.0.Temperatures are 37-55 ( • C) and the time is 4 h [161].The antioxidant capacity can be proven by several methods, as shown in Figure 6.

Figure 6 .
Figure 6.Type of methods used to demonstrate antioxidant activity.

Figure 6 .
Figure 6.Type of methods used to demonstrate antioxidant activity.

Figure 7 .
Figure 7. Diseases treated with antioxidant nutraceuticals that have in their compositions peptides and collagen hydrolysates.

Figure 7 .
Figure 7. Diseases treated with antioxidant nutraceuticals that have in their compositions peptides and collagen hydrolysates.

Table 1 .
Marine collagen isolated from marine vertebrates and invertebrates.Marine species, tissue from marine organism, extraction method, extraction time and yield, physicochemical methods of characterization, and type of isolated collagen.

Table 2 .
Amino acids from fish collagen from skin and other subproducts.

Table 4 .
Antioxidant activity of various marine species due to the composition of different amino acid sequences tested by different physicochemical methods.

Table 5 .
Antioxidant activity for different marine species generated by different amino acid sequences evidenced by different specific enzymatic hydrolysis methods and different types of physicochemical analysis methods.

Table 6 .
The biological activities of collagen hydrolysates, collagen peptides, and amino acid sequences from different marine organisms with results in the treatment of different diseases are systematized.