Marine Bioactives

Abstract

Marine organisms are a rich source of bioactive compounds. Bioactive compounds are compounds with health-promoting effects. Consumption of these compounds may lower the risk of diseases such as heart diseases, cancer, diabetes, osteoporosis, and other complications. Recently, marine bioactives have attracted much attention due to their enormous health benefits. This book chapter provides a succinct review of the recent studies about marine bioactives including proteins, peptides, amino acids, fatty acids, sterols, polysaccharides, oligosaccharides, phenolic compounds, photosynthetic pigments, vitamins, and minerals. It also discusses the bioactives derived from marine bacteria as well as different techniques used for marine bioactives recovery.

6.1 Introduction

More than 70% of the earth is covered by the seas, oceans and aquatic environments. Many living creatures including aquatic plants and animals exist in these environments with potential health benefits that have not been discovered yet. Many studies have been conducted so far to explore the world under the water and to find a cure for many diseases that the world population is dealing with. However, we are yet far from exploring these valuable resources of the aquatic world. Earlier studies with Greenlandic Inuit or Eskimos indicated that having a great number of seafoods in the diet increases well-being and health (Bang et al. 1986; Rangel-Huerta and Gil 2018). This was probably the milestone of a series of studies on the effect of seafood consumption on human body. Since that time, scientists found that marine organisms including plant and animals contain bioactive compounds which may promote health in human being. According to these studies, marine organisms may provide bioactive compounds with different activities including anticoagulant, calcium-binding, anti-obesity, and anti-diabetic, antioxidant, anti-hypertensive, anti-HIV and anti-proliferative activities (Bleakley and Hayes 2017; De Jesus Raposo et al. 2013; Abdul et al. 2016). Thus, this chapter discusses the bioactive compounds of different types of marine organism. It also reviews their applications in health, cosmetic and food industries.

6.2 Marine Proteins

Proteins have a fundamental, physiological and nutritional role in the human body as major structural components of all cells. They also act as hormones, enzymes, and antibodies and have a critical role as carries in both cell walls and blood. On top of that, proteins e.g. collagen provide structural support in connective tissues, cells, and skin. As a food component, proteins have essential nutritional roles by providing energy and amino acids which are vital for growth and maintenance in our body. Foods from marine resources are generally recognized as a great source of proteins containing all the essential amino acids close to the proportion suitable for human beings (Hamed et al. 2015). Marine animal-based foods contain relatively higher proportion of protein on a wet weight basis (average 17.3%) than meats from terrestrial animals (13.8%), despite having a higher moisture content than most terrestrial meats (Tacon and Metian 2013). Marine animals muscle usually contains lower amount of stroma proteins (e.g. collagen and elastin) than red meat which ranges from 1 to 3% in finfish up to 10% in shark and ray fish. Myofibrillar protein content in marine animals ranges between 65 and 75% and it ranges between 20 and 35% for sarcoplasmic proteins (Venugopal 2008). Marine invertebrates e.g. oyster, mussel, clam, and squid exceptionally have another type of protein in their strained muscles called paramyosin which ranges between 3 and 19%. Proteins from marine animals have high digestibility and biological value as well as having essential amino acids especially lysine much higher than proteins from plant foods (Wang et al. 2018). These proteins are also rich in amino acids e.g. methionine and lysine which are limited in terrestrial meat proteins (Tacon and Metian 2013; Khalili Tilami and Sampels 2018).

Beyond their nutritional value, recent studies have shown that proteins from marine foods and their hydrolysates can also exert health effects on the human body. For many years, health effects of seafoods consumption such as dyslipidemia and heart diseases have been attributed to high content of mega-3 fatty acids found in their oil. However, most recent studies have shown that marine proteins may also play a key role in beneficial health effects of marine foods. Various physiological health effects and bioactivities such as mitigating effects on obesity, metabolic syndrome, inflammation, type II diabetes (insulin sensitivity or glucose tolerance), cardiac risk factors (high blood pressure and triacylglycerol levels), osteoporosis, and reduced circulating concentrations of lipids have been reported for marine proteins in either animal models or human trials which are summarized in Table 6.1 and briefly reviewed in the following.

Table 6.1 Bioactive properties of fish proteins studied in animal models

6.2.1 Antiobesity Properties of Marine Proteins

Obesity which is morphologically seen as overweight and extra body fat accumulation is as worldwide health issue. This excessive body weight has shown strong association with heart disease risk factors e.g. insulin resistance, type-2 diabetes, dyslipidemia, metabolic syndrome, and high blood pressure. Several studied have shown that sole inclusion of fish protein in diet can effectively protect against obesity-related disorders especially formation of adipose tissue mass in animal models as summarized in Table 6.1. For example, a diet with a mixture of several marine protein sources (ling, rosefish, cod, wolfish and muscle from a scallop) could reduce fat mass in rats compared with the diets containing a mixture of chicken, pork, and beef as main protein source (Holm et al. 2016). However, the effects of preventing obesity were more evident in cod protein containing diets. Proteins from other fish including salmon, herring, bonito, and mackerel were also added to high fat diet and their effects on rats were compared with diets with casein. Despite equal energy intake among all groups, it was an only salmon protein-containing diet that significantly reduced weight gain (Pilon et al. 2011). These two studies suggest that beneficial physiological effects of marine proteins are highly governed by their sources. The latter study also found that consumption of salmon diet also increased circulating calcitonin levels in the rats which might have also played role in reduction of weight gain in the studied rats. Salmon calcitonin is a widely studied bioactive peptide in fish protein with 32 amino acids with blood calcium lowering activity 40–50 times more potent than human calcitonin (Aadland et al. 2015). It has been clinically used for more than 30 years for treatment of metabolic bone disease e.g. osteoporosis, paget disease, and bone metastases by inhibiting osteoclast activity (Pilon et al. 2011).

6.2.2 Hypolipidemic Properties of Marine Proteins

Another reported health benefit for marine food proteins is related to their effects on lipid metabolism which is also related to coronary artery disease. Animal studies have shown that defatted protein from Alaska Pollak could decrease serum cholesterol in rats through the inhibition of cholesterol and bile acid absorption and the enhancement of cholesterol catabolism in the liver (Hosomi et al. 2009). Also, similar beneficial effects have been observed in both rabbits fed with cod protein compared to casein and milk proteins and in rat fed with herring and salmon protein hydrolysates (Bergeron and Jacques 1989; Drotningsvik et al. 2016). When protein from crab, scallop, cod, and chicken was tested on obesity-prone mice, a significant reduction in lipid metabolization was found in scallop fed mice (Tastesen et al. 2014). Scallop protein could significantly reduce plasma triacylglyceride, non-esterified fatty acids, glycerol and hydroxybutyrate in mice. Most of the mentioned studies have used fillet or muscle of marine animals as a source of protein in their studies. However, a more recent study by Drotningsvik et al. (2018) have evaluated anti-obesity effects of water soluble proteins from a pelagic fish called blue whiting. Obese rats fed with a diet containing the water soluble proteins (1/3 of protein in their diet) from blue whiting had lower levels of serum and liver cholesterol compared to rats fed with 100% of casein in their diet. This was most likely related to lower hepatic cholesterol synthesis in the rats fed with the water soluble proteins.

In line with the above mentioned animal studies, a randomized control trial comparing the effects of consuming protein from cod, pollock, saithe, and scallops with lean meat: chicken, beef, turkey, pork, egg, and low-fat milk in a Norwegian group found a reduction in both fasting and postprandial circulating triglycerides concentrations in the participants (Aadland et al. 2015). Also, cod protein supplementation to thirty-four overweight adults for 8 weeks could help lipid metabolism in the participants and reduce LDL cholesterol (Vikoren et al. 2013).

6.2.3 Antidiabetic Properties of Marine Proteins

Type 2 diabetes is another health issue associated with obesity and related to sugar metabolism in the body. In this disorder, the human body becomes resistant to the effect of insulin or loses the capacity to produce insulin. Some studies have shown that seafood and even fish protein can reduce insulin resistance and thereby increase capacity to store glucose as glycogen and minimize the risk of type 2 diabetes (Nkondjock and Receveur 2003). For instance, feeding rats with a high-fat, high-sucrose diet containing cod protein (having 91% protein and 0.19% lipid) as protein source completely hindered the development of insulin resistance and glucose intolerance in the animals (Lavigne et al. 2001). Control rats fed with the same diet but containing soy protein isolate and casein as protein sources showed improvement in fasting glucose tolerance and peripheral insulin sensitivity (Lavigne et al. 2000). Nevertheless, insulin resistance was detected in the rats fed with soy protein and casein. The author showed that the ability of cod protein in preventing insulin resistance caused by obesity in those rats could be partly related to the direct effect of amino acids in the cod protein on insulin-stimulated glucose uptake in skeletal muscle cells (Lavigne et al. 2001). In line with the previous studies, feeding rats with diet containing salmon protein also promoted their insulin sensitivity (Pilon et al. 2011). Ochiai et al. (2015) showed that defatted protein produced from dried bonito fish (Katsuwonus pelamis) could effectively diminish the bone frailty caused by insulin resistance and type 2 diabetes mellitus in young rats (Ochiai et al. 2015). This study could confirm that fish protein can also be a marine bioactive that can potentially help in mitigating bone frailty independent from the effects found for poly unsaturated fatty acids.

A more recent randomized double-blind study on 93 overweight adults evaluated the effect of protein from herring and salmon protein hydrolysate as well as cod protein on glucose regulation and markers of insulin sensitivity in the participants (Hovland et al. 2019). The participants received the fish proteins (2.5 g/day) as well as a mixture of casein and whey (as control) as tablet. They did not report fat content in the proteins. The study showed that consumption of the low dosage of cod protein or herring protein hydrolysates could promote glucose regulation in overweight adults. However, they did not find any significant effect for salmon protein hydrolsyate (Hovland et al. 2019).

6.2.4 Antihypertensive Properties of Marine Proteins

Blood pressure or hypertension is another important risk factor for cardiovascular disease which is the largest cause of death globally (Vasdev and Stuckless 2010). Normal blood pressure should be 120/80 mmHg and elevation of one or both parameters causes heart workload increase and results in a condition called hypertension (Jensen and Mæhre 2016). The beneficial effects of marine proteins on hypertension have been studied in both animal models and less frequently in clinical trials. For example, a 20% replacement of intact fish protein in the diet of spontaneously hypertensive rats (SHR) for 8 weeks significantly reduced blood pressure in the animals compared to those eating the casein protein (Ait-Yahia et al. 2003; Ait Yahia et al. 2005). A more recent study showed that a diet containing 20% of sardine protein and 2% of lemon zest induced a significant decrease of diastolic blood pressure and heart rate values in rendered diabetic and hypertensive rats compared with casein containing diet (Khelladi et al. 2018). Also, purified protein from sardine by-products could induce lowered blood pressure in obese rats compared with casein (Affane et al. 2018). Although studies on the effects of intact marine proteins are rare, a large number of studies have shown that total protein hydrolysates from different marine sources such as salmon (Enari et al. 2008), cod (Jensen et al. 2014), cobia (Yang et al. 2013) and jellyfish (Liu et al. 2012) have significant blood pressure reducing effect on SHR. Also, evaluations on chronic effect of total protein hydrolysates from some marine sources such as seabream (Fahmi et al. 2004) and jellyfish (Liu et al. 2012) on SHR have shown a significant reduction of blood pressure even comparable to that of captopril. When it comes to human studies the results are not easily judged. For example, a randomized trial with 33 medicated patients with coronary heart disease showed that cod protein as main protein source in diet could reduce both systolic and diastolic blood pressure in the patients (Erkkilä et al. 2008). However, supplementation of salmon protein hydrolysate capsules to overweight adults for 2 months had no effect on blood pressure of the patients (Enari et al. 2008).

6.2.5 Anti-Inflammation Properties of Marine Proteins

Inflammation is normally considered as a regular reaction of our immune system to harmful stimuli which has a critical role in our life. However, inflammation disorder can cause a vast variety of diseases such as cancer, atherosclerosis, and ischemic heart disease, colitis, Crohn’s disease and so on. Anti-inflammatory effects of omega-3 containing fish oil are widely agreed but recent studies have shown that fish proteins and most probably their hydrolysate may have anti-inflammatory effects.

For example, defatted cod protein added to the diet of rats with artificially injured muscle promoted resolution of inflammation in their muscles compared to casein and defatted peanut protein. The cod protein could significantly reduce density of neutrophils and ED1+ macrophages at day 14 and 24 post injury in the injured muscles of the rats (Dort et al. 2012). Addition of defatted peanut protein to the diet of the rats with injured muscles had no anti-inflammatory effect and even reduced their muscle mass recovery (Dort et al. 2012). The authors later showed that the anti-inflammatory effect observed for cod protein is related to its high levels of arginine, glycine, lysine and taurine by supplementing casein with a mixture of those amino acid in similar amount to their levels in cod protein (Dort et al. 2016). In a later study, Dort et al. (2016) reported similar anti-inflammatory effects for shrimp protein hydrolysate in rats with artificially injured muscle. Anti-inflammatory activity was also reported for proteins from four different fish species including bonito, salmon and herring and mackerel. Proteins from the named fish could mitigate expression of both tumor necrosis factor–α and interleukin-6 in visceral adipose tissue of rat compared with casein (Pilon et al. 2011).

6.2.6 Brain Health Effects of Marine Proteins

Age-related diseases such as dementia and Alzheimer’s disease that are progressive disorders causing brain cell death and loss of memory are also growing in the aging population around the world. Beneficial effects of fish consumption against the cognitive related disease have been widely studied but it has been mainly related to the function of omega-3 fatty acids (Kühn 2014). However, a recent study has shown that parvalbumin which is recognized as most common allergen in fish can cause cross-reactions with human amyloidogenic proteins and inhibits amyloid formation of α-synuclein which is mostly associated with neurodegenerative disorders such as Alzheimer’s and Parkinson’s (Werner et al. 2018). The authors suggested that beneficial effects of fish on brain health might be also partly explained by its protein function. However, further studies are needed to make a concrete conclusion in this regard.

6.2.7 Marine Algae Proteins and Their Bioactivity

Proteins from marine plants i.e. seaweed and microalgae are also an emerging type of marine proteins that have gained massive attention recently as more sustainable and marine origin vegetarian protein alternatives. Proteins in seaweed are a structural component of their cell wall and have physiological roles as enzymes and pigments (Pimentel et al. 2019). Protein contents in seaweeds can reach up to 47% dry weight in Rhodophyceae (red seaweeds) and 9–26% dry weight in Chlorophytes (green seaweeds), followed by the lowest at about 3–15% in Phaeophytes (brown seaweeds). However, protein content of seaweeds varies substantially by change in season and geographical locations and environmental conditions (Okolie et al. 2018).

Two typical proteins found in seaweeds with bioactive properties are lectin and phycobiliproteins. As glycoproteins with high specificity binding with carbohydrate, lectins have found a wider range of application e.g. in blood grouping, anti-viral (including human immunodeficiency virus type 1(HIV-1)), cancer biomarkers, and targets for drug delivery (Bleakley and Hayes 2017). Lectins from algal sources have also shown other bioactive properties such as antinociceptive, antibacterial, antiviral, antiadhesion, cytotoxic, and mitogenic properties (Okolie et al. 2018).

Phycobiliproteins are photosynthetic proteins that have critical role in light capturing in red seaweeds. They are water-soluble and inherently fluorescent which makes them a useful biomaterial for application in some immunological methods (Pal and Suresh 2016). Phycobiliproteins are also used as natural colorants in the food and cosmetic industry. In addition, these proteins have shown a wide range of bioactive properties such as hepatoprotective anti-inflammatory activities, antitumor, antioxidant, antiviral and neuroprotective properties (Bleakley and Hayes 2017). These multifunctional bioactivities of phycobiliproteins have led to their application in treatment of some disease e.g. arteriosclerosis, serum lipid reduction, and lipase inhibition (Okolie et al. 2018).

Protein hydrolysates and peptides generated by enzymatic hydrolysis of proteins from a wide range of seaweeds have also shown several bioactive properties such as antioxidant (Heo and Jeon 2008; Wang et al. 2010), antihypertensive (Athukorala and Jeon 2005; Cian et al. 2012), antiproliferative (Athukorala et al. 2006) and antidiabetic (Harnedy et al. 2015) properties. However, results are mainly limited to in vitro studies which call for more research on animal models and human trials for a better understanding of their application potentials. This has also made seaweeds as one of the fastest-growing research fields for recovery of marine origin bioactive compounds.

Altogether, recent studies have shown that health benefit effects of marine foods go beyond their omega-3 PUFAs and their protein can play a significant role in their bioactivity. However, more human studies in clinical and intervention trials on pure and especially defatted marine proteins are needed to support bioactivities found in vitro models and animal models. Also, effects of processing, storage and cooking methods on the bioactivity of marine proteins need to be considered in future studies and recommendations.

6.3 Marine Peptides

Peptides are short chains of amino acids connected with peptide bonds with usually between 3 to 20 amino acids (Jo et al. 2017). Bioactive peptides may naturally exist in marine organisms to perform some physiological roles in their body or be generated artificially by enzymatic hydrolysis of marine proteins. The enzymatic hydrolysis method has gained great attention in the food industry and it has been used for extraction of bioactive peptides from a wide range of marine resources such as fish, crustaceans, mollusks, algae, and microorganisms, especially during the last two decades. Different types of marine animals such as fish, shrimp, lobster, crab, mussel, clam, jellyfish, sea cucumber, sea urchin, squid, oyster, sponges, rotifers and etc. have been used for production of bioactive peptides using enzymatic hydrolysis (Proksch et al. 2010; Bordbar et al. 2011; Ngo et al. 2012; Harnedy and FitzGerald 2012; Jo et al. 2017). In addition, seafood industry has already lost more than 50% of its biomass as by-product e.g. fish head, frame, tail, bone, skin, viscera, blood and shells which have been targeted as a great substrate for production of marine bioactive peptides (Atef and Mahdi Ojagh 2017; Ishak and Sarbon 2018).

Bioactive peptides are inactive within the parent protein structure but as soon as they are released using the hydrolysis, they show various bioactive properties depending on their amino acid composition and sequence (Ngo et al. 2012). Thanks to the almost endless number of variations that can happen in amino acid composition and sequence, marine bioactive peptides have shown several types of bioactivity including antihypertensive, antiproliferative, anticancer, antioxidant, antimicrobial, anti-inflammation, anticoagulant and opioid agonists or antagonists properties (Proksch et al. 2010; Bordbar et al. 2011; Ngo et al. 2012; Harnedy and FitzGerald 2012; Samarakoon and Jeon 2012; Jo et al. 2017). In the light of these explanations, bioactive peptides may be able to potentially improve human health and reduce disease risk as nutraceuticals and pharmaceuticals. In parallel, promotion in consumers’ awareness about the association between food and health has led increase in demand for functional foods (Jo et al. 2017). Thus, bioactive peptides produced from marine organisms, representing more than 50% of our global biodiversity, can be a great source of bioactive compounds to be used as nutraceuticals and functional foods (Kim and Wijesekara 2010; Suleria et al. 2015). Thus, in the following, an overview of most recent bioactive peptides produced from different marine resources as well as seafood processing by-products and their bioactive properties is presented.

6.3.1 Marine Peptides with Antioxidant Activity

Antioxidants play an important role in our body by reducing negative effects from the excessive generation of reactive oxygen species (ROS) such as superoxide anion (O²⁻) and hydroxyl (OH¹⁻) radicals. However, imbalance between generation of ROS and ability of endogenous antioxidants in human body in their detoxification can cause oxidative stress. This imbalance has been associated with several chronic health issues such as heart disease, stroke, high blood pressure, cancer, inflammatory disease and aging (Valko et al. 2007). Bioactive peptides with ability to scavenge free radicals and ROS or stopping lipid peroxidation by interrupting the radical chain reaction have been extracted from protein hydrolysate of different marine animals and plants. These peptides are normally called antioxidant peptides and have been isolated from fish and shrimp muscle and their processing by-products e.g. head (Yang et al. 2011; Chi et al. 2015a), frame (Je et al. 2005, 2007), skin (Zhang et al. 2012), bone (Baehaki et al. 2015), swim bladder (Zhao et al. 2018), viscera (Villamil et al. 2017), and shrimp peeling by-products (Ambigaipalan and Shahidi 2017). For example Chi et al. (2015b) extracted three antioxidant peptides from tuna head by-products with sequence of Trp-Glu-Gly-Pro- Lys (WEGPK), Gly-Pro-Pro (GPP), and Gly-Val-Pro-Leu-Thr (GVPLT), with molecular weights of 615.69, 269.33, and 485.59 Da, respectively. The antioxidant activity of the isolated peptide was most likely related to high concentration of hydrophobic and/or aromatic amino acid residues in their sequence. However, the mechanism of their antioxidant activity was different where GPP indicated highest in vitro radical scavenging activity (IC₅₀ = 1.9-2.4) but WEGPK inhibited the peroxidation of linoleic acid. Also, a peptide (Lys-Thr-Phe-Cys-Gly-Arg-His) with molecular weight of 86.1 kDa produced from croaker (Otolithes ruber) muscle with enzymatic hydrolysis could promote the endogenous cellular antioxidant enzymes in Wistar rats (Nazeer et al. 2012). The peptide elevated the activities of catalase (CAT), glutathione-S-transferase (GST) and superoxide dismutase (SOD) in the animals.

Other marine animals including crab (Yoon et al. 2013), squid (Sudhakar and Nazeer 2015), oyster (Umayaparvathi et al. 2014; Zhang et al. 2019a), mussel (Wang et al. 2013), clam (Chi et al. 2015a), jellyfish (Zhuang et al. 2009a), and sea cucumber (Zhou et al. 2012) have been used for production of antioxidant peptides. For example, Sudhakar and Nazeer (2015) could separate a 679.5 Da peptide from cuttlefish (Sepia brevimana ) by enzymatic hydrolysis with the sequence of Ile/Leu-Asn-Ile/Leu-Cys-Cys-Asn with a remarkable inhibition of linoleic acid auto-oxidation in a model system.

Marine algae are also considered as a rich source for isolation of antioxidant peptides due to their highly unstable living conditions in ocean experiencing extraordinary low light intensities and high oxygen concentrations (Samarakoon and Jeon 2012). For example, a peptide with sequence of Glu-Leu-Trp-Lys-Thr-Phe recovered from enzymatic hydrolysis of Gracilariopsis lemaneiformis proteins with α-chymotrypsin showed a significant free radical scavenging activity with an EC₅₀ value of 1.514 mg/ mL (Zhang et al. 2019b). The authors suggested low molecular weight and hydrophobic and/or aromatic amino acids in the sequence of the purified peptides as main reason for its relatively good antioxidant activity.

6.3.2 Marine Peptides with Antihypertensive Properties

Peptides produced form marine organisms have been widely investingated as bioactives with antihypertensive properties. Antihypertensive peptides can modulate physiological regulation of blood pressure by inhibiting the activity of angiotensin-I converting enzyme (ACE) (Abdelhedi and Nasri 2019). ACE can regulate blood pressure by converting angiotensin-I to angiotensin-II. The later is a potent vasoconstrictor and also inactivates the vasodilator bradykinin (Li et al. 2004). Side effects created by treatment of blood pressure with synthetic ACE inhibitors such as captopril, enalapril, alcacepril have made interest in finding natural alternatives including bioactive peptides (Kim and Wijesekara 2010). From a mechanistic point of view, synthetic drugs inhibit ACE by blocking its action while ACE inhibitory peptides react with ACE and prevent its attachment to Angiotensin I (Ngo et al. 2012). However, the mechanism of action has not been well understood for some bioactive peptides. Numerous studies have shown antihypertensive activity of marine-derived bioactive peptides in both in vitro and in vivo. Bioactive fractions obtained by enzymatic hydrolysis of cobia head with papain showed an ACE inhibitory IC₅₀ of 0.24 mg/ml which was intensified after incubation with gastrointestinal enzymes (Yang et al. 2013). Oral administration of the bioactive peptides to SHR in a dosage of 150–1200 mg/kg body weight could reduce systolic blood pressure in a dose-dependent manner in the rats. Similar blood pressure-lowering effect was found in SHR fed with bioactive peptides from jellyfish Rhopilema esculentum (IC₅₀ = 1.28 mg/ml) (Liu et al. 2012), oyster (IC₅₀ = 66 μmol/L) (Wang et al. 2008), sea bream scale collagen (IC₅₀ = 0.57 mg/ml) (Fahmi et al. 2004), yellowfin sole (Limanda aspera) frame (IC₅₀ = 28.7 μg/ml) (Jung et al. 2006), bigeye tuna dark muscle (Thunnus obesus) (IC₅₀ = 26.6 μM), chum salmon (Oncorhynchus keta) skin (IC₅₀ = 18.7 μM) (Wang et al. 2008).

The antihypertensive effect of marine bioactive peptides has been also reported in some human studies. For example, daily administration of 3 g of a 3 kDa permeate of protein hydrolysate from dried bonito could significantly reduce systolic blood pressure in borderline and mildly hypertensive human subjects (Fujita et al. 2001). Also, 300 and 500 mg daily uptake of protein hydrolysate from a seaweed (Undaria pinnatifida) showed the same effect in mildly hypertensive subject groups consuming its jelly after 8 weeks (Kajimoto et al. 2002). Similarly, a daily intake of 1.6 g oligopeptide from Nori (Porphyra yezoensis) resulted in a significant reduction of systolic blood pressure in participants with high-normal blood pressure after 12 weeks (Kajimoto 2004). In addition, consumption of a beverage (100 ml) containing 2 g of salmon muscle protein hydrolysate for 12 weeks significantly reduced systolic and diastolic blood pressure in 60 mildly and high-normal hypertensive participants (Enari et al. 2007; Norris et al. 2013).

6.3.3 Marine Peptides with Antiproliferative and Anticancer Properties

Cancer is one of the top leading causes of death among the global population and is continuously increasing which has made it a big threat for the global population (Ezzati et al. 2002). Cancer is the abnormal growth and uncontrolled proliferation of cells caused by certain mutations in cellular DNA which destabilize cell division and death process (Le Gouic et al. 2019). This uncontrolled cell division can finally lead the formation of tumor which may limit its location or invade and spread to other parts of body (Ezzati et al. 2002). Production of antiproliferative peptides that can induce cell death by apoptosis has gained interest as a way for treatment of cancer. Different peptides from marine organisms have shown antiproliferative and anticancer properties. Among the studied organisms that can produce toxins; sponges, mollusk and tunicates have been the most effective and studied aquatic organisms (Suarez-Jimenez et al. 2012). However, peptides with antiproliferative effect have been also isolated from other marine organisms such as marine snails (Kim et al. 2013), oyster (Umayaparvathi et al. 2014) and fish (Song et al. 2014) and snow crab by-products (Doyen et al. 2011). Two peptides with molecular weight ranging from 390 to 1400 Da separated from enzymatic hydrolysate of tuna dark muscle showed antiproliferative activity against human breast cancer cell line MCF-7 (Hsu et al. 2011). The purified peptides had an amino acid sequence of Leu-Pro-His-Val-Leu-Thr-Pro-Glu-Ala-Gly-Ala-Thr and Pro-Thr-Ala-Glu-Gly-Gly-Val-Tyr-Met-Val-Thr. The two peptides exhibited a dose-dependent inhibition effect of the cancer cells with IC₅₀ values of 8.1 and 8.8 μM. Also, a peptide with amino acid sequence of YALPAH from hydrolysate of half-fin anchovy (Setipinna taty) induced PC-3 cell apoptosis at the concentration of 4.47 μM (Song et al. 2014). The peptide showed an IC₅₀ of 8.1 mg/ml and its antiproliferative activity was correlated to its positive charge intensity in a way peptide with the highest positive charge intensity showed the strongest antiproliferation. Anticancer peptides found in the studied hydrolysates from marine organisms have all had very low molecular weight and all contained active amino acids including Pro, Gly, Lys, Arg, and Tyr. This might be because low molecular weight peptides have higher mobility and diffusivity than larger peptides which facilitates their interaction with cancer cells and promote their anticancer activity (Ishak and Sarbon 2018).

6.3.4 Marine Peptides with Skin, Bone, and Joint Health Effects

Several factors including chronological aging, dermatological disorders, and environmental conditions can cause skin properties loss. This can be even intensified undesirable lifestyle and photo-aging (Fu et al. 2018). Collagen peptides from marine foods have gained great interest as a sustainable ingredient with antiaging and skin health promotion properties. A large number of studies have shown that collagen peptides from different marine sources such as fish scale (Wang et al. 2017) fish skin (Pyun et al. 2012) and jellyfish (Zhuang et al. 2009b; Fan et al. 2013) could increase collagen production in rats and significantly decrease matrix metalloproteinases (MMP) expression. For example, Song et al. (2017) showed that ingestion of collagen peptide from silver carp skin at 50, 100 and 200 mg/kg body weight increased moisture contents of the skin of mice subjected to UV-induced photoaging. It also significantly increased the skin components and improved the antioxidative enzyme activities in both serum and skin of the animals. In addition, they found that low molecular peptides were more effective than high molecular weight collagen peptides. In contrast, ingestion of gelatin (>120 kDa) from silver carp did not lead to any significant change compared to control mice. Later Liu et al. (2019) showed that collagen peptides form silver carp skin promotes the photoaging skin cell repair by activating the TGF-β/Smad pathway to promote procollagen synthesis and suppressing AP-1, MMP-1 and MMP-3 protein expression to prevent collagen degradation. Similarly, oral ingestion of collagen hydrolysate from Nile tilapia scale increased the collagen content and antioxidant enzyme activities and improved the appearance and structure of skin after 6 months in mice (Wang et al. 2017).

A clinical study on 64 individuals for 12 weeks evaluated the effect of collagen peptides from catfish skin on human skin hydration and elasticity, and wrinkling when it is orally consumed. This randomized controlled trial showed that daily intake (1000 mg/day) of low-molecular-weight collagen peptide from the fish skin significantly promoted hydration, elasticity, and wrinkling in human skin (Kim et al. 2018). It has been also shown that gelatin hydrolysate from fish skin resulted in significantly higher content of hydroxyproline-containing peptides in human blood compared with gelatin hydrolysate from porcine in 5 h after ingestion (Ohara et al. 2007; Ichikawa et al. 2010). This means collagen source can affect quantity and structure of hydroxyproline-containing peptides in human blood after their oral administration which would govern their health benefit. This may suggest marine collagens as a more promising source for functional food development. However, further clinical studies are needed to fully support this.

Bone related disorders such as osteoporosis and osteoarthritis are also considered as a common disease in the global aging population (Daneault et al. 2017). Marine collagen peptides have also shown a positive effect in treatment of osteoporosis, joint disorders, and osteoarthritis (Aleman and Martinez-Alvarez 2013). For example, collagen hydrolysate from silver carp skin improved mineral density, increase bone hydroxyproline content, enhance alkaline phosphatase level and reduce tartrate-resistant acid phosphatase 5b (TRAP-5b) activity in serum of chronologically aged mice (Zhang et al. 2018). Also, a significant reduction of bone loss was observed in mice supplemented with collagen hydrolysate from fish compared to a control protein suggesting benefits of hydrolyzed collagen for osteoporosis prevention go beyond the effect of simple protein supplementation (Wauquier et al. 2019).

Altogether, bioactive peptides from marine resources have shown a wide range of bioactive properties which have made them a promising source for the development of functional foods as a route to benefit from these biologically active ingredients in human health promotion. However, further studies on the efficacy of marine bioactive peptides when added to food products is needed.

6.4 Marine Amino Acids

Seafood products such as fish, crustaceans, and mollusks are very good sources of essential amino acids (EAA) and contain proteins with a very high biological value. Proteins from marine animals are a rich source of methionine (5.9 to 6.4% of total EAA) and lysine (18.2–19.6% of total EEA) (Tacon and Metian 2013). This makes marine products a good substitute for these amino acids which are normally considered as limiting amino acids in plant-based proteins. Marine plants especially brown seaweeds are also a reach source of aspartic acid and glutamic acid. Other abundant amino acids in edible seaweeds e.g. Palmaria palmata and Enteromorpha include histidine, leucine, isoleucine, methionine, and valine (Pal and Suresh 2016). Also, content of valine, threonine, isoleucine, leucine, methionine, and phenylalanine in Sacharine latissima and proteins from this brown seaweed met the WHO/FAO’s adult and infant recommended dietary intake level set by WHO/FAO/UNU (Abdollahi et al. 2019).

Marine foods are also considered as an important source of taurine which is a biologically active amino acid. Taurine is naturally occurring Sulphur-containing amino acid (2-aminoethanesulphonic acid) in the human body which does not include in protein sequence or structure, but it plays very important biological role in our body. A wide range of biological actions including beneficial effect on cardiovascular health, protection against ischemia-reperfusion injury, modulation of intracellular calcium concentration, and antioxidant, antiatherogenic and blood pressure-lowering effects have been reported for taurine (Xu et al. 2008). It can be partially synthesized in the body, but diet is the main source of taurine in healthy people. Seafoods especially mollusks are rich source of taurine and a large part of seafood health benefits has been associated with their high levels of taurine. For example, Dragnes et al. (2009) reported a range of 57 mg/100 g in haddock to 510 mg/100 g in blue mussel when studying different seafood including cod fillet, salmon fillet, saith fillet, haddock fillet, cod roe, peeled shrimp and deshelled mussel. Among the studied fish fillets, saithe had the highest content with 162 mg/100 g. They also found substantially higher content of taurine in cod roe, shrimps and blue mussel than all the studied fish fillets. A level of 70 and 240 mg/100 g wet weight has been also reported for oyster and clam (Lourenço and Camilo 2002; Harnedy and FitzGerald 2012). However, taurine content of seafood products can be strongly affected by processing conditions, cooking, and storage. Since taurine is a water-soluble compound, products subjected to soaking, brining or washing experience a great loss of taurine compared to freshly caught products (Dragnes et al. 2009).

6.5 Marine Oils and Fatty Acids

Marine food products are considered as the major food source of long-chain omega-3 fatty acids especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). A great scientific and public interest has been created toward consumption of marine omega-3 polyunsaturated fatty acids since studies found a significantly lower incidence of cardiovascular disease (CVD) in Greenlandic Inuit or Eskimos having a great number of seafoods in their diet compared to Western populations (Bang et al. 1986; Rangel-Huerta and Gil 2018). Long-chain omega-3 fatty acids including EPA and DHA are very insufficiently produced from their plant origin precursor alpha-linolenic acid in human body (Keefe et al. 2019). Thus, they must be necessarily provided by our diet and/or supplementation with marine fatty acids. Marine foods are in general considered as a rich source of long-chain omega-3 fatty acids but there is large variation in the content of these fatty acids among different types of seafood.

6.5.1 Marine Sources of Omega-3 Fatty Acids

The muscle of fatty fish such as salmon , trout, herring, mackerel, sardine, anchovy, albacore and tuna contains high amounts of EPA and DHA. For example, 100 g of cooked salmon and herring or 200 g of sardine can provide 2 g of EPA +DHA. This will cover the recommendations for daily intake of omega-3 fatty acids (0.25–2 g) by World Health Organization (Itsiopoulos et al. 2018). Demersal fish such as cod and halibut store oil mainly in their liver thus have low content of EPA and DHA in their muscle.

Fish oil is also a very important source of long-chain omega-3 and is the richest available source of EPA and DHA. Global production of fish oil is around 0.8–1 million tons which are mainly produced from whole pelagic fish including anchoveta, sardine, capelin, blue whiting, menhaden, and herring especially in southwest America (Auchterlonie 2018). Also, almost a quarter of global fish oil is produced from fish processing by-products which its share is increasing as a more sustainable alternative. More than 75% of global fish oil production is used for animal feeding, especially in aquaculture. Around 21% of its global production is directly used for human consumption as omega-3 capsules, infant formulas and pharmaceuticals and functional food supplements which are expected to have major growth in demand for fish oil (Seafish 2018). Although the major part of fish oil is used for feed, still marine oils are one of the most popular supplements in the world. For example, marine origin omega-3 products are used by 6.5% of the population in the USA which represents 37% of supplement users in the country (Albert et al. 2016).

Other emerging marine sources of omega-3 fatty acids are krill and algae and copepods oil as shown in Fig. 6.1. Krill oil contains high levels of phospholipids and represents a good source of EPA and DHA up to 12–50 g of long-chain omega-3 fatty acids per 100 g oil depending on species (Adarme-Vega et al. 2014). Krill oil is mainly produced by harvesting a krill species known as Euphasia superba and compared to fish oil stores 30–65% of long-chain omega-3 fatty acids as phospholipids while it is mainly stored as triglycerides in fish oil (Burri and Johnsen 2015). Several studies have shown that since cell membrane is made of phospholipids, this similarity may increase physiological fatty acid absorption of krill oil compared to fish oil (Andraka et al. 2019). Some review papers have recently gathered researches on bioavailability and health benefits of krill oil (Burri and Johnsen 2015; Andraka et al. 2019). Recently a Norwegian company called Calanus has started marketing oil extracted from a small copepod called Calanus finmarchicus as a new source of marine long-chain omega-3 fatty acids. Omega-3 fatty acids are mainly stored as wax esters in this copepod and are sold as the only commercially available marine source of wax esters.

Fig. 6.1

Marine sources of omega-3 fatty acids can be directly consumed as seafood products or used for the production of fish oil and omega-3 concentrates

Marine microalgae are another emerging source of marine omega-3 fatty acids which is considered as a vegetarian and sustainable marine alternative. Microalgae are primary producers of long-chain omega-3 fatty acids which are later accumulated in other marine organisms including krill and fish. They can have oil content of 10-50% of their body weight which can store omega-3 as 30–70% of their fatty acids (Martins et al. 2013).

6.5.2 Health Benefits of Marine Omega-3 Fatty Acids

Marine omega-3 polyunsaturated fatty acids are among the most studied and documented food bioactives with health benefits during the last four decades and some of their health benefits are summarized in Fig. 6.1. Beneficial health effects of marine omega-3 polyunsaturated fatty acids on CVD by preventing sudden cardiac death, congestive heart failure, and ischemic stroke have been reported in many clinical studies and reviewed by Bowen et al. (2016) and Elagizi et al. (2018). Recently 3 large randomized control trials on the potential benefits of marine omega-3 fatty acids on the occurrence of CVD have been conducted (Keefe et al. 2019). First study was done on 8179 patients suffering from coronary heart disease and showed that daily intake of highly purified omega-3 product (4 g/day) containing EPA reduced the risk for major adverse CVD by 25% (Bhatt et al. 2019). The two other large trials were conducted in primary prevention populations (Bowman et al. 2018; Bhatt et al. 2019). They also indicated that daily intake of purified fish oil (1 g/day) providing 840 mg/day of EPA and DHA significantly diminished risks of death due to coronary heart disease. It was especially effective in those who did not consume fish and seafood frequently (Bowman et al. 2018; Bhatt et al. 2019). The authors concluded that high doses of marine omega-3 fatty acids should be consumed for patients with coronary heart disease on statins having elevated triglycerides and in primary prevention for people who do not consume at least 1.5 meals of seafood/week (Keefe et al. 2019).

Omega-3 fatty acids especially DHA are primary structural fatty acids in the brain membrane phospholipids thus their beneficial neuroprotective effects against dementia have been also reported (Karr et al. 2011). A large number of studies have also evaluated the effects of omega-3 fatty acids on cognitive decline or Alzheimer’s disease (Sinn et al. 2010). Long-chain omega-3 fatty acids have a vital role for normal development of brain and their levels decrease in the brains of people with Alzheimer’s disease (Karr et al. 2011; Shahidi et al. 2018). Studies with biological and animal models have shown that omega-3 fatty acids can improve blood flow, reduce inflammation and/or amyloid-β pathology which giving them ability of primary prevention of cognitive decline (Fotuhi et al. 2009; Jicha and Markesbery 2010). This is in line with observational studies on human which also suggests consumption of omega 3 fatty acids can reduce cognitive decline with aging (Canhada et al. 2018). However, Fotuhi et al. (2009) concluded in their review that the existing data may support the role of these fatty acids in slowing cognitive decline in elderly people without dementia, but not for the prevention or treatment of dementia, including Alzheimer disease.

Other important health benefits reported for marine long-chain omega-3 fatty acids includes preventing or slowing the progression of age-related macular degeneration (Ghasemi Fard et al. 2019; Punia et al. 2019), anticancer properties (Manson et al. 2019). It has been also reported that they can reduce oxidative stress (Heshmati et al. 2019), and have immuno-modulatory activity. This makes them a prominent supplement recommended for prevention or treatment of inflammatory disorders e.g. rheumatoid arthritis (RA), Crohn’s disease, ulcerative colitis, psoriasis, asthma, lupus and cystic fibrosis (CF) (Ruxton et al. 2004).

6.6 Marine Sterols

Sterols are a group of lipids that are also found in marine organisms with different biological roles as hormones and signaling molecules (Pal and Suresh 2016). They are also a structural component of cell membrane providing membrane fluidity and permeability. Sterols have been isolated from different marine sources such as diatoms (Belt et al. 2018) and sponges (Heidary Jamebozorgi et al. 2019) but marine algae are considered among the most important marine sources of bioactive sterols (Abdul et al. 2016). The main type of sterol found in brown algae is fecosterol while red algae contain mainly cholesterol and green algae (Chlorophyceae) contain mainly Taergosterol and 24-ethylcholesterol (Sánchez-Machado et al. 2004). A wide range of biological activities have been also reported for sterols from marine organisms including antioxidant, antidiabetic, anti-inflammatory and anti-HIV properties, anticancer activity, hepatoprotective, antiobesity, anti-osteoarthritic and anti-osteoporotic effects as well as anti-hyperlipidemic and anti-arteriosclerosis effects (De Jesus Raposo et al. 2013; Abdul et al. 2016).

6.7 Marine Polysaccharides

Marine animals that are used as muscle food contains normally low contents of polysaccharides but shells of crustaceans such as shrimp and crab as well as squid pen are a rich source of chitin which is one of the most important marine polysaccharides (Fig. 6.2). Chitin or poly (β-(1-4)-N-acetyl-D-glucosamine) is the second most abundant polysaccharide on the earth which is industrially produced from marine shell waste stream (Ngo et al. 2015). However, chitin has poor solubility due to its crystalline structure which limits its application. Thus, chitin is converted to chitosan which is generated by deacetylation of chitin through enzymatic or chemical processes. Chitosan is soluble in weakly acidic solutions and has antioxidant and antimicrobial properties. It is widely used for biomedical applications such as drug delivery, wound healing, tissue regeneration, as well as food protection, agriculture, textile, cosmetics, paper making and wastewater treatment (Muxika et al. 2017). Also a recent systematic review of randomized controlled trials by Huang et al. (2019) concluded that chitosan consumption might be a useful adjunctive pharmacological therapeutic tool for bodyweight management, particularly in overweight/obese participants.

Fig. 6.2

Marine polysaccharides and their potential animal and algae sources

Another bioactive polysaccharide extracted from marine animals is chondroitin sulfate which is a sulfated glycosaminoglycan. Cartilage of some marine animals such as shark and ray for many years have been considered a good source of this polysaccharide. More recently other marine sources such as sea cucumber (Myron et al. 2014), fish (Vázquez et al. 2016) and shrimp by-products (Palhares et al. 2019) have been introduced as alternative marine sources for extraction of chondroitin sulfate. It is an essential component of the extracellular matrix of connective tissues. This glycosaminoglycan has various biological and vital roles in human body. This ranges from help in function and elasticity of the articular cartilage and hemostasis up to regulation of cell development, cell adhesion, proliferation and differentiation (Vázquez et al. 2013). A wide range of commercial products of chondroitin sulfate is marketed as nutraceuticals with cartilage regeneration, anti-inflammatory activity and osteoarthritis properties (Volpi 2009). The products mainly contain low/medium-molecular weight chondroitin sulfate (inferior to 20 kDa) and are orally consumed to treat and prevent osteoarthritis (Michel et al. 2005; Vázquez et al. 2013).

Hyaluronic acid, also called hyaluronan, is another polysaccharide or more exactly a mucopolysaccharide which is naturally found in organisms (Vázquez et al. 2013). It has a huge number of medical applications e.g. ophthalmic surgery, orthopedic surgery and rheumatology, drug delivery systems, pulmonary pathology, joint pathologies, and tissue engineering (Giji and Arumugam 2014). It has been traditionally extracted from terrestrial sources, but more sustainable sources especially marine organisms have recently attracted great attention. It has been isolated from some marine animals such as bivalve mollusk Amussium pleuronectus (Kanchana et al. 2013), fish eyeball (Amagai et al. 2009; Murado et al. 2012), liver of marine stingray Aetobatus narinari (Sadhasivam et al. 2013). Sulfated polysaccharides have been also isolated from some marine animals such as sponges (Jridi et al. 2018), clam (Souissi et al. 2019) and tuna processing by-products (Jridi et al. 2018).

Algae, especially seaweeds, are the most important sources of marine bioactive polysaccharides. Brown seaweed is a source of alginate, fucoidans, and laminarin (Fig. 6.2) (Fedorov et al. 2013). Fucoidans are a group of sulfated polysaccharides that have structural role in cell wall of brown seaweeds and are one of the most studied marine polysaccharides during the last decade (Sanjeewa et al. 2017). Fucoidans have shown a wide range bioactive properties including antiviral, anticoagulant, antitumor, anti-inflammation, anti-allergy, antiobesity and antioxidant properties (Vo and Kim 2013). Laminarin is also a polysaccharide with a small molecular weight (∼5 kDa) found in brown seaweeds which has shown different bioactive properties such as anticancer, anti-inflammatory, anticoagulant, and antioxidant effects (Kadam et al. 2015). Both fucoidans and laminarins are considered as interesting marine bioactive compounds for application in functional foods.

Red seaweeds are the source of sulfated galactan (agars and carrageenans), xylans, and floridean starch (Pal and Suresh 2016). Carrageenans are also a group of sulfated polysaccharides with great interest in food industry due to their excellent physical properties, such as thickening, gelling, and stabilizing abilities (Jiao et al. 2011). At low molecular weight they have also shown different bioactive properties e.g. as promising anticancer and antitumor activities possibly due to their antiviral and antioxidant properties, and stimulation of antitumor immunity (Raman and Doble 2015).

Green algae contain ulvan, starch, xylans, mannans, and ionic polysaccharides which contain sulfate groups. Uronic acids, rhamnose, xylose, galactose, and arabinose are also found in this type of algae (Pal and Suresh 2016). Ulvan is a water-soluble sulfated polysaccharide found in green seaweed of the order Ulvales and it has the gel-forming capacity and several bioactive properties and health benefits which have been reviewed in may papers (Kim and Li 2011; Ngo and Kim 2013).

6.8 Oligosaccharides

Sugar molecules consisting of 2–10 monosaccharide units are called compound sugar or oligosaccharides. Many functions have been reported for oligosaccharides extracted from marine resources including immunostimulant, antioxidant, anticarcinogenic and antitumor effects (Mussatto and Mancilha 2007). Some of the oligosaccharides may be used as prebiotics to promote probiotic bacterial growth. Examples include xylooligosaccharides and fructooligosaccharides which cannot be digested in the gastrointestinal tract and act as prebiotics. Some of the most important marine oligosaccharides are chitin, carrageenan, agar, and alginate oligosaccharides which are produced by chemical or enzymatic hydrolysis of their primary polysaccharides. Food applications of marine oligosaccharides have been reported as low-sweetness humectants and bulking agents. They are also used as stabilizers in cosmetic industry (Lordan et al. 2011).

6.9 Phenolic compounds

Macro and microalgae contain-antioxidant compounds called polyphenolic compounds. Phenolic acids, hydroxycinnamic acids, simple phenols, coumarins, xanthones, naphthoquinones, flavonoids, stilbenes, anthraquinones and lignins are 10 classes of polyphenolic compounds that can be recovered or isolated from marine organisms (Ibañez et al. 2012). For instance, extract of marine brown algae such as Eisenia bicyclis, Ecklonia kurome, H. fusiformis, and Ecklonia cava polyphenolic is called phlorotannins. This bioactive compound imparts many functions including antioxidant, antibacterial, chemo-preventive, UV-protective, and antiproliferative effects… Eckol, phlorofucofuroeckol A, dieckol, and 8,8-bieckol which are few examples of phlorotannins have been effective against phospholipid peroxidation Shibata et al. (2007) experimented these phlorotannins and found out that they resemble ascorbic acid and tocopherol in terms of antioxidant activity.

6.10 Photosynthetic Pigments

These are pigments that are able to absorb solar energy for photosynthesis. Mainly, carotenoids and chlorophyll in macroalgae are the photosynthetic pigments. Carotenoids act as antioxidants, and provitamin A. They have anticancer, and cardioprotective effects. They are also effective against macular degeneration. β-carotene and astaxanthin are generated by microalgae and have been employed in food industry. Examples of these microalgae include Dunaliella salina, Haematoccous pluvialis, Nanochloropsis oculat, Chlorerlla sorokiniana (Pizarro and Stange 2009).

Dunaliella salina is used for mass production of the β-carotene and it can produce β-carotene up to 14% of its dry weight (Miyashita 2009). Cultivation of the Dunaliella salina is easier than the other plants and produces both cis and trans isomers of carotene with high bioavailability. In addition, under irradiance stress, Dunaliella salina accumulates a large amount of zeaxanthin which contributes to disease preventions (Yeum and Russell 2002).

Haematoccous pluvialis , is cultivated in both open and closed culture systems and produces chlorophylls and carotenoids. Haematoccous pluvialis, is able to produce astaxanthin as 1.5–3% of its dry weight under stress conditions. Several European countries and USFDA approved Haematoccous pluvialis, as a dietary supplement for human consumption. Astaxanthin has 10 times stronger activity than carotenoids which promotes anticancer, anti-inflammatory effects. That is why astaxanthin has been utilized by nutraceutical, cosmetics and food and feed industry (Rasmussen and Morrissey 2007).

Some of the reported bioactivities of the β-carotene include free-radical scavenging which alleviates the issues with coronary heart disease, cancer, premature aging, and arthritis. Carotenoid extract of Chlorella ellipsoidea exerted strong antiproliferative effect on human colon cancer cells, including induction of apoptosis (Klassen 2010).

Chlorophylls which are mainly produced by all classes of algae and cyanobacteria have been used as a coloring agent in food and drinks. They also impart anticancer effects. Marquez and Sinnecker (2007) found that dietary chlorophyll exhibits antimutagenic effects and reduces tumor cell growth. Diet high in chlorophyll may also reduce the risk of colon cancer.

Astaxanthin is a type of carotenoid which is found in yeast, salmon, trout, krill, shrimp, and crayfish. Astaxanthin supplementation of obese mice diet showed a decrease in body weight, skeletal muscle and adipose tissue (Yuan et al. 2011). Studies also have shown that insulin resistance could be alleviated using astaxanthin. This could be related to activation of post-receptor insulin signaling (Arunkumar et al. 2012). It appears that the greatest amount of astaxanthin can be found in Haematococcus pluvialis which is a chlorophyte algae. Astaxanthin has been effective to reduce cardiovascular risk markers of oxidative stress and inflammation according to clinical studies. It has been also effective for improving blood status (Riccioni et al. 2011; Yuan et al. 2011).

Chlorophylls extracted from brown algae have antioxidant activities in methyl linolenate systems. Normally chlorophyll b shows stronger antioxidant effect than chlorophyll a due to the presence of an aldehyde group in chlorophyll group b. However, the mechanism of action is unknown (Lanfer-Marquez et al. 2005).

Neither carotenoids nor chlorophyll can be synthesized by animal tissues. Thus, these molecules must be obtained from food, particularly seafood organisms are the major sources of these compounds.

Phycobiliproteins are a class of pigments (composed by a protein and chromophore called phycobilin) in marine red algae such as Porphyridium cruentum and cyanobacteria which are used as fluorescent markers when linked to antibodies, A-protein, biotin, lectins, and hormones (Aneiros and Garateix 2004). Phycocyanin and phycoerythrin are two of the most known phycobiliproteins. They act in the immune system and anti-inflammatory agents. Phycocyanin is also used in perfumes and eye makeup powders as well as food colorants due to its stability (Kadam and Prabhasankar 2010).

Fucoxanthin extracted from Hijikia fusiformis is also one of the main antioxidant molecules with free radical scavenging activity. This activity might be due to double allenic bonds at the C-70 position (Sachindra et al. 2007). Fucoxanthinol has been extracted from Undaria pinnatifida. Undaria pinnatifida also contains another metabolite called halocynthiaxanthin. Both metabolites have antioxidant activity. Studies have shown that fucoxanthin has higher antioxidant activity than fucoxanthinol and halocynthiaxanthin due to the presence of an allenic bond.

6.11 Vitamins

B vitamins particularly vitamins B₁, B₂ and B₁₂ are found in large quantities in seaweeds. According to Kim and Taylor (2011), two-third of the human requirement of vitamin C and adequate amount of vitamins A, B₂ and B₁₂ can be obtained through consumption of 100 g of seaweed. Vitamin B₁₂ is mainly found in some of the red macroalgae such as Palmaria longat and Porphyra tenera and green seaweeds. However, the highest concentration of vitamin B₁₂ is 0.768 mg/kg for Porphyra. Vitamin B₁₂ is also found in microalgae (Spirulina platensis) at 7 mg/kg. Vitamin B₁₂ is a co-factor enzyme and cobalt-containing tetrapyrrole related to chlorophyll and heme. Megaloblastic anemia, chronic fatigue syndrome, and neuropsychiatric disorders are few serious conditions due to vitamin B₁₂ deficiency. Red and brown algae are the excellent sources of folic acid and folate derivatives.. For instance, 100 g of dry Undaria pinnatifida provides 150 μg folic acid (Misurcova 2011). Dunaliella salina is a halophile green micro-algae which is a great source of β-carotene (provitamin A), as well as thiamine, pyridoxine, riboflavin, nicotinic acid, biotin and tocopherol (Drokova and Popova 1974).

Vitamin C or ascorbic acid acts as an antioxidant as well as immune system support. This vitamin is found in Spirulina platensis at high concentration (80 mg/kg). It is also found in Porphyra umbilicalis which traditionally consumed to prevent scurvy (Karleskint et al. 2012). While Undaria pinnatifida and Laminaria digitate are significant sources of vitamin E and C, diatom Haslea (Navicula) ostrearia is particularly rich in vitamin E. P. cruentum is another microalga rich in vitamins C, E (tocopherols) (Lordan et al. 2011).

The best sources of vitamin D are fatty fish. Nannochloropsis oculate is one of the algae that contain vitamin D as well. Rickets in infants and children and osteomalacia in adults are among the diseases due to vitamin D deficiency (Luten 2009).

Vitamin E is a mixture of tocopherols including α-, β-, and γ-tocopherols. Red, green and brown seaweeds are the main sources of α-tocopherol. β- and γ-tocopherols are mainly found in Phaeophycean. Vitamin E is useful in cardiovascular disease prevention and it has antioxidant activities. type of seaweed processing as well as seasonal, environmental and physiological changes all may influence the vitamin E content. For instance, α-tocopherol in dehydrated Himanthalia longate and canned Himanthalia longate was 33.3 and 12 μg/dry weight, respectively (Ravishankar et al. 2005).

6.12 Minerals

Macroalgae are great sources of minerals. Geography, season and environmental condition of the harvested seafood all affect the mineral contents of the macroalgae. U. pinnatifida, sargassum and Chondrus crispus, Gracilariopsis can be considered as a dietary supplement to the daily intake of minerals such as Na, K, Ca and Mg, as well as trace minerals like Fe, Zn, Mn and Cu (Taboada et al. 2010).

Osteoporosis and hypocalcia are two of the conditions caused by Ca deficiency in the diet. Ca is also needed during lactation and pregnancy. The high amount of Ca is found in seaweeds. Fishbone which is considered a fish processing by-product is also a good source of Ca. Almost 30% of the fishbone is collagen however, 60–70% of the fishbone is composed of Ca, phosphate and hydroxyapatite. Fishbone can be incorporated into food products. However, they should become soft enough to be edible. In order to make them edible, different techniques and methods such as hot water treatment and acetic acid solutions are used (Nguyen et al. 2011).

Hydroxyapatite is another compound from fishbone which can be used for rapid bone repair after major trauma or surgery because it is stable at physiological pH and functions actively in bone bonding.

The most promising characteristic of seaweed is high I content which is an important factor in growth patterns and metabolic regulations. Kelp is one of the seaweeds which contains high amount of I. Production of thyroid hormones such as thyroxine and triiodothyronine depend upon I in the diet. Stillbirth, abortion, cretinism, goiter and mental disorders are few ailments due to lack of enough I in the diet (MacArtain et al. 2007).

Some of the minerals in seafoods are more abundant than land animals or plants. For instance, Palmaria palmata is a seaweed and an excellent source of iron which contains 8 g/serving of dry algae. This amount of iron is even higher what is found in 100 g of raw sirloin steak. However, high content of arsenic in some seaweeds is a place of concern for their direct consumption as food (MacArtain et al. 2007).

6.13 Bioactive Compounds Derived from Marine Bacteria

Several biologically important bioactive compounds can be extracted from bacteria that live in marine environment. Most of these bacteria live under harsh conditions including high pressure, cold and dark situations. However, regardless of these conditions, they produce valuable bioactive compounds that are necessary to study.

6.13.1 Antibacterial Effects

Marinispora (strain NPS008920) is a marine actinomycete that has been isolated from Cocos Lagoon, Guam. This strain was found in the sediment samples collected from this area. The compositional analysis of this strain revealed a series of novel 2-alkylidene-5-alkyl-4-oxazolidinones, lipoxazolidinone A, B, and C. These compounds have shown potent antibacterial activities similar to linezolid (Zyvox) which is a commercial antibiotic. Minimum inhibitory concentration (MIC) tests showing that this antibiotic has potent antibacterial activity with 1.56–15.57 mM against gram-positive bacteria and 37.38 mM against two strains of Haemophilus influenzae (Barbachyn and Ford 2003).

Marinispora is a marine actinomycete. A new strain of this genus called NPS12745 was found in the sediments off the coast of San Diego, California. Two important marine antibiotics i.e. chlorinated bisindole pyrroles, and lynamicins A-E were discovered in this strain. These two antibiotics have shown strong antibacterial activity against S. aureus (MSSA, MRSA: methicillin-resistant), Staphylococcus epidermidis and Enterococcus faecalis. Therefore, this strain has the potential to be used in combat against those infections that have been caught in a hospital and are potentially caused by organisms that are resistant to antibiotics (McArthur et al. 2008).

Pseudomonas stutzeri (CMG 1030) is one of the 100 species of bacteria that was found in the intestinal tract of fish collected from the Baluchistan coast in which borders the Gulf of Karachi, Pakistan, Pseudomonas stutzeri (CMG 1030) showed potent antibacterial effect against different types of pathogens including MRSA strains. zafrin (4b-methyl-5,6,7,8-tetrahydro-1(4b-H)-phenanthrenone) is an ethyl acetate extract of Pseudomonas stutzeri (CMG 1030) which was able to kill Bacillus subtilis faster than ampicillin, vancomycin or tetracycline. The mechanism of action for zafrin is similar to nisin and it does not disintegrate the bacterial cell wall

and Triton X-100, which disrupts the cell membrane. It was suggested that the mode of action of zafrin is via the disruption of the cytoplasmic extract collected from red alga Laurenica spectabilis in Ras-Gharib coast of the Red Sea, Egypt is active against pathogenic microorganisms with MIC of 0.1–10 mg ml⁻¹. This extract was effective against most of the Gram-positive and Gram-negative bacteria as well as against pathogenic fungi such as Candida albicans, Aspergillus niger and Botrytis fabae (Isnansetyo et al. 2003).

6.13.2 Anticancer Effects

Marine bioactive compounds have been also explored for anticancer effects. Micromonospora marina is a bacterium which was found in In 1997 in soft corals of Indian oceans. the mycelial extract of this bacterium contains a novel depsipeptide named thiocoraline Clinical studies revealed that Thiocoraline is able to inhibit DNA polymerase-a. PharmaMar is a pharmaceutical company that currently studies this compound for commercialization (Romero, et al. 1997; Newman and Cragg 2004).

Marine fungus Curvularia sp. (strain no. 768) was found on a red alga called Acanthophora spicifera. The macrolide apralactone A, a 14-membered phenyl acetic acid macrolactone, as well as six further curvularin macrolides that were extracted from this fungus, have shown anticancer activity against 36 human tumor cell lines (Greve et al. 2008).

6.13.3 Antidiabetic Effects

Diabetes mellitus is a condition that the body does not produce enough insulin and as a result, the blood glucose level is high. The number of patients is increasing annually throughout the world (World Health Organization 1985). Aquastatin A is a compound that was isolated from a marine fungus Cosmospora sp. SF-5060 which was found at Gejae Island, Korea. Studies have shown that this compound has strong inhibitory effect against protein tyrosine phosphatase 1B (PTP1B).

Further analysis revealed that the EC50 value of this compound is 0.19 mM. PTP1B is able to regulate the insulin and leptin receptor-mediated signaling pathways. Therefore, it could be future solution to diabetes and its complications (Seo et al. 2009).

6.14 Extraction Techniques for Marine Bioactives

6.14.1 Super Critical Fluid Extraction (SFE)

This method was proposed by Hannay and Hogarth in 1879. SFE is a method that uses solvents at temperature and pressure above their critical points. The major advantage of this technique is minimum use of toxic organic solvents. The most commonly used solvent is carbon dioxide (CO₂) to extract natural resources such as marine bioactives. Although CO₂ is an environmentally friendly solvent which is considered as GRAS for use in food industry, however, low polarity of the CO₂ is one of the major drawbacks that should be solved by using cosolvents or polar modifiers to change the polarity of the CO₂ (Björklund et al. 2005). Methanol at 1–10% may be used to expand the CO₂ range of polarity . Propane, butane, and dimethyl ether have also been proposed to use to increase the polarity of the CO₂. However, none of these solvents fulfill the principles of Green Chemistry. As for marine bioactives extraction, CO₂ has the benefit of high diffusivity, and ease of tuning the temperature and pressures that have been applied. Also, utilization of CO₂ provides a solvent-free extraction method. CO₂ can be easily converted from liquid form to gas after completion of the extraction for ease of recovery (Ibañez et al. 2012).

6.14.1.1 Application of SFE to Macroalgae, Microalgae, and Cyanobacteria

As we discussed earlier, due to the low polarity of CO₂, this method is beneficial for compounds with low polarity. However, if CO₂ used at mild pressure and temperature conditions, it allows obtaining volatile compounds without affecting its properties. The volatile compounds produced by aquatic organisms play a critical role in chemical defense mechanisms and food gathering of the organisms. Microalgae share their ecological niche with bacteria and other microorganisms. As a result, microalgae secrete compounds with antibacterial, antifungal, and often antiprotozoal activities (El Hattab et al. 2007). For instance, the extract obtained from Dunaliela salina which is a green microalga using the SFE method with CO₂ at 314 bar and 9.8 °C showed strong antimicrobial activity against the pathogens Escherichia coli, Staphylococcus aureus, Candida albicus, and Aspergillus niger. This activity is probably due to the presence of indolic compounds, polyunsaturated fatty acids, and compounds related to the metabolism of carotenes such as β-ion-one and neophytadiene in microalgae extract (Mendiola et al. 2005).

Bioactive lipids such as essential fatty acids also are extracted using the SFE. For instance, Spirulina platensis was studied for this purpose. The maximum extraction yield was obtained at 350 bar and 40 °C and a flow rate of 24 kg/CO₂/h. Similarly, vitamin E extraction was studied in Spirulina and a tocopherol enrichment of more than 12 times the initial concentration of the tocopherol in raw material by extraction with neat CO₂ at 361 bar and 83.3 °C was achieved. Carotenoids were also extracted from Chlorella vulgaris and Spirulina. The addition of polar modifiers such as ethanol in the supercritical CO₂ allowed the extraction of more polar carotenoids but also chlorophylls, thus decreasing the selectivity of the extraction process. Other bioactive compounds such as diolefins have been extracted from Botrycoccus braunii using SFE. Botrycoccus braunii is able to store large number of hydrocarbons with long-chain (25–31 carbon atoms) which can be used as a substitute for paraffinic and natural waxes (Mendiola et al. 2005).

Phenolic compounds from marine resources have been also extracted using the SFE method. A hyphenated technique was used to isolate isoflavones from sea macroalgae. In this technique, samples are pretreated using sonication, followed by extraction using SFE with modified CO₂ and 3% of MeOH/H₂O mixture at 350 bar and 40 °C for 60 min (Klejdus et al. 2010).

6.14.1.2 Application to Invertebrates

Bioactive compounds from invertebrates such as crustacean including krill, crawfish, crab or shrimp as well as squid, urchin, and starfish have also been extracted using the supercritical CO₂ method (Félix-Valenzuela et al. 2001).

Astaxanthin, the pigment responsible for the orange-pink coloration of the crustacean is abundant in their shell waste. They are also able to modify some carotenoids such as β-carotene and transform them into astaxanthin. For the first time, Yamaguchi and his colleagues in 1986 were able to apply SFE to crustacean waste. They extracted nonpolar lipids, mainly triglycerides and astaxanthin from krill using one-step extraction utilizing SC-CO₂ at 60 °C and 245 bar.

Sea urchin gonads and squid viscera are rich in PUFA which are normally discarded. However, these are nutritious from a human nutritional standpoint (Zhu et al. 2010). Palmitic, oleic, eicosapentaenoic acid and docosahexaenoic acid were extracted from squid viscera using SC-CO₂ with 1.5% ethanol and temperatures between 25 °C and 50 °C and pressure range from 80 to 170 bar (Chun et al. 2010).

6.14.2 Pressurized Liquid Extraction (PLE)

There are different names for pressurized liquid extraction including pressurized fluid extraction (PFE), enhanced solvent extraction (ESE), high-pressure solvent extraction (HPSE) or accelerated solvent extraction (ASE). The main advantage of this method is the simultaneous application of pressure and a liquid with a temperature higher than its boiling point. Therefore, it reduces the amount of solvent that is needed for extraction, so it is considered as a green extraction technique. It also allows for faster extraction of materials. (Turner and Ibañez 2011).

6.14.2.1 Applications to Macroalgae, Microalgae, and Cyanobacteria

Reduced extraction time and the possibility of automation are some reasons for popularity of the PLE method for recovery of bioactive compounds from marine resources. Carotenoids from Dunaliella salina were extracted using PLE and the results showed that the temperature is the main factor that influences the recovery. The best yield was with ethanol at 160 °C and 17.5 min (Breithaupt 2004).

Carotenoids such as fucoxanthin and other oxygenated carotenoids from brown macroalgae such as Eisenia bicyclis, Cytoseira abies-marina, and Himanthalia elongate have been isolated using pressurized liquid extraction. It has been reported that this technique could be used to extract bioactive compounds from cyanobacteria or algae as well (Shang et al. 2011).

6.14.3 Pressurized Hot Water Extraction (PHWE)

This method is also known as subcritical water extraction, pressurized low water (PLPW) extraction, or superheated water extraction (SHWE) is a particular use of PLE with water as extracting solvent. This method uses water at temperatures above the atmospheric boiling point. However, it keeps it in the liquid form by using the pressure. Water is the greenest solvent can be used (Teo et al. 2010).

6.14.3.1 Application to Macroalgae, Microalgae, and Cyanobacteria

PHWE at high temperatures may generate new antioxidant compounds. Plaza et al. (2010) used this technique to study the antioxidant properties of Chlorella vulgaris and Sargassum vulgare. The application of this technique at high temperatures may produce new compounds with antioxidant activities.

6.14.4 Ultrasound-Assisted Extraction (UAE) and Microwave-Assisted Extraction (MAE)

In an ultrasound-assisted extraction system, acoustic cavitation is used disrupt the cell walls and reduce the particle size of the target compounds as well as enhancement of the contact between the solvent and the target compounds. However, in microwave-assisted extraction, the microwave radiation is used to induce movement of polar molecules and rotation of dipoles to heat solvents and to promote transfer of target compounds from the sample’s matrix into solvent (Ying et al. 2011).

6.14.4.1 Application to Macroalgae, Microalgae, and Cyanobacteria

Mainly carotenoids were extracted using this technique from microalgal genus Dunaliella. The prosses performed on Dunaliella tertiolecta led to rapid pigment extraction mainly because of the absence of frustule in microalgae cells thus allowing immediate solvent penetration (Pasquet et al. 2011).

6.14.4.2 Application to Marine By-Products

The bioactive compounds from fish processing by-products have not been studied using MAE method. fatty acid profile composition of the lipids recovered from cod liver and mackerel fillet using this technique were studied by Batista et al. (2001). Mackerel fillet and cod liver contained lipid content of 5.6% ± 0.4% and 62.6% ± 3.1%, respectively. These results indicated that application of microwave-assisted extraction could be a replacement for the conventional method due to its efficiency.

6.14.5 Isoelectric Solubilization and Precipitation

Isoelectric solubilization and precipitation (ISP) is a method of recovery of proteins and lipids from seafood and seafood processing by-products. Generally, processing fish into fillets generates large quantitates of by-products including trimming, heads, fish frames, skin and scale which are normally discarded. However, these by-products are valuable and nutritious resources of highly functional proteins and omega-3 fatty acids that if recovered properly cane be added to food products. Tahergorabi et al. (2015); Tahergorabi et al. (2012) and Tahergorabi et al. (2011) have applied this method to isolate the protein fish whole fish as a model for fish processing by-products as well as poultry products.

The ISP process is carried out in five steps. In the initial step, the fish or fish processing by-products are ground and homogenized with a ratio of 1:6 (w: w) of water. In the second step, the pH of the solution is adjusted to 11.50 ± 0.05 with 10N NaOH. In the third step, the homogenate is transferred to centrifuge tubes and centrifuged at 10,000 × g. This step separates the solution into three layers including the fat on the top, protein solution in the middle and the insoluble and impurities at the bottom. In the fourth step, the protein solution is transferred to a beaker and the pH is adjusted to isoelectric point (5.5 ± 0.05) with 10N HCl. In the last step, the solution is centrifuged, and the protein is recovered from the solution.

6.15 Conclusions

Extracts of marine organisms have demonstrated bioactive properties that impart health benefits. The bioactive compounds not only are extracted from the marine organisms but also are extracted from their processing by-products. Hence, they have attracted much attention from food, cosmetic and drug industries in the past few years. As a result, many methods have been designed to extract these valuable compounds from marine resources. Incorporation of these compounds in food may also offer functional food products that could target specific health issues. However, this may emerge the issue of overexploitation of the marine resources. Therefore, responsible and sustainable strategies must be devised to use these limited and valuable resources.