Seaweeds as a Functional Ingredient

Seaweeds as a Functional Ingredient: Comparison

Please note this is a comparison between Version 1 by Gema Nieto and Version 2 by Peter Tang.

Seaweeds are autotrophic organisms of simple structure with little or no cellular differentiation and complex tissues, so they are talophytes. They are classified taxonomically into three groups—Chlorophyta, Phaeophyceae, and Rhodophyta, corresponding to green, brown, and red algae, respectively.

seaweeds
lipids
proteins
dietary fibre
polyphenols
functional food

1. Introduction

For several centuries, there has been a traditional use of seaweed as food in China, Japan, and Korea, as well as in some Latin American countries such as Mexico. The migration of the people from these countries around the world has meant that this custom has moved with them, so today, there are many more countries where seaweed consumption is not unusual. In recent years, there has been a strong movement in France to introduce seaweed into European cuisine, with some success, although it is still considered an exotic component of the menu. It has gained more acceptance in regions such as California and Hawaii, where Japanese communities are larger, and the taste for seaweed is spreading to the surrounding population as it is found in restaurant dishes and on supermarket menus. In fact, in Austria and Germany, seaweeds are being used to produce a highly prized bread—algenbrot, a blend of cereals whose composition is up to 3% seaweed. In Brittany, dulse and kombu are used to make the bara mor or “bread of the sea,” and minced seaweed in butter (beurre des algues) is used for cooking fish or spreading on bread to accompany shellfish ^[1].

2. Nutritional Evaluation of Algae

The chemical composition of algae depends on the species, place of cultivation, atmospheric conditions, and harvesting period. From a nutritional point of view (

1. Introduction

2. Nutritional Evaluation of Algae

The chemical composition of algae depends on the species, place of cultivation, atmospheric conditions, and harvesting period. From a nutritional point of view (

Table 1), algae are an important source of proteins and lipids. In general, protein contents was higher in green and red seaweeds (10–47% of dry weight—DW) than those found in brown seaweeds (5–24% DW); in lipids (from 0.79% to 7.87% dry matter), ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) constitute a significant part of the lipid profile of seaweeds ^{[2][3][4][5][6][7][8]}.

On the other hand, dietary fiber is recognized today as an important element for healthy nutrition. However, there is no universal definition or analytical method that measures the food components that exert the physiological effects of fiber, but there is consensus that the definition should include the physiological role of dietary fiber ^[9]. Therefore, it can be said that dietary fiber consists of a series of compounds comprising a broad mixture of carbohydrates and polymers present in plants, including both oligosaccharides and polysaccharides, such as cellulose, hemicellulose, pectic substances, gums, resistant starch, and inulin, which may be associated with lignin and/or other non-carbohydrate components (polyphenols, waxes, saponins, cutins, and resistant protein) ^[10].

), algae are an important source of proteins and lipids. In general, protein contents was higher in green and red seaweeds (10–47% of dry weight—DW) than those found in brown seaweeds (5–24% DW); in lipids (from 0.79% to 7.87% dry matter), ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) constitute a significant part of the lipid profile of seaweeds [14,15,16,17,18,19,20].

On the other hand, dietary fiber is recognized today as an important element for healthy nutrition. However, there is no universal definition or analytical method that measures the food components that exert the physiological effects of fiber, but there is consensus that the definition should include the physiological role of dietary fiber [21]. Therefore, it can be said that dietary fiber consists of a series of compounds comprising a broad mixture of carbohydrates and polymers present in plants, including both oligosaccharides and polysaccharides, such as cellulose, hemicellulose, pectic substances, gums, resistant starch, and inulin, which may be associated with lignin and/or other non-carbohydrate components (polyphenols, waxes, saponins, cutins, and resistant protein) [22].

Table 1.

Chemical composition of different algae (g/100 g dry weight—DW).

	Seaweed			Protein			Lipids			Ashes			Ref.

], so fruits and vegetables are poor sources of vitamin B12, which explains why vitamin B12 deficiency is common among people following strict vegetarian or vegan diets [51,52,53].

Table 3.

Mineral content in different algae (mg/100 g DW).

						Macro-Minerals														Micro-Minerals
	Seaweed			Ca			K			Mg			Na			P			Fe			Mn			Zn			Cu			Ref.
					Chlorophyta

Cystophora retroflexa [82]. In addition to phlorotannins, other polyphenols have been described, such as fucol and its derivatives, flavonoids, and derivatives such as catechin and epicatechin [8].

Table 4.

Polyphenols content in different algae.

	Seaweed			Total Polyphenols			Ref.
										Chlorophyta
Caulerpa lentillifera		9.26 ± 0.03
Caulerpa lentillifera			1874.7		1.57 ± 0.02			1142.7	22.20 ± 0.27			1028.6		^[11]	[23]
	8917.5			-			21.37		-			3.51			0.11		^[26]	[36]	Ulva clathrata
Ulva rigida		27.2 ± 1.1				524.5		2.2 ± 0.1		1561.0			27.5 ± 0.2			2094.1		^[3]	[15]
	1595.0			210.0			283.0		1.60			0.60			0.50		^[44]	[54]	Ulva lactuca	8.46 ± 0.01		7.87 ± 0.10		19.59 ± 0.51
										Rhodophyta																	^[	^4]	[16]
					Rhodophyta
Chondrus crispus		420.0			3184.0			732.0		4270.0			-			3.97			1.32		7.14		<0.50	^[12]	[24]	Chondrus crispus
Ellisolandia elongata (formerly		27.2 ± 1.4		Corallina mediterranea)	2.0 ± 0.1			45,075.2		759.3		21.1 ± 0.1				4977.4		^[12]^[13]^[14]	[24,25,26]
	2457.7			-			27.70		6.27			3.02			0.69		^[45]	[55]	Garateloupia turuturu
Jania rubens		22.9 ± 2.0			42,344.0		2.6 ± 0.1		327.5		18.5 ± 0.6				2986.6		^[2]	[14]
	2086.2			-			47.50		9.53			2.63			0.36		^[45]	[55]	Jania rubens	11.28 ± 0.10		2.05 ± 0.09
Palmaria palmata		44.03 ± 0.45		^[15]	[		1000.027]
		2700.0	Porphyra/Pyropia spp.		26.6 ± 6.3			2.1 ± 1.2		20.6 ± 0.2		^[7]^[12]	[19,24]
Pterocladia capillacea (formerly Pterocladia capillacea)		20.67 ± 0.03			2.19 ± 0.09			17.50 ± 0.28	^[15]	[27]
					Phaeophyceae
Ascophyllum nodosum		8.70 ± 0.07			3.62 ± 0.17			30.89 ± 0.06	^[16]	[28]
Bifurcaria bifurcata		8.92 ± 0.09			6.54 ± 0.27			31.68 ± 0.41	^[16]	[28]
Durvillaea antarctica		11.6 ± 0.9			4.3 ± 0.6			25.7 ± 2.5	^[5]	[17]
Fucus vesiculosus		12.99 ± 0.04			3.75 ± 0.20			20.71 ± 0.04	^[16]	[28]
Laminaria spp.		6.3 ± 3.8			1.0 ± 0.3			37.6 ± 0.4	^[7]^[12]	[19,24]
Saccharina latissima		25.70 ± 0.11			0.79 ± 0.07			34.78 ± 0.08	^[6]	[18]
Sargassum fusiforme		10.9 ± 1.0			1.4 ± 0.1			-	^[7]	[19]
Undaria pinnatifida		18.9 ± 9.8			4.5 ± 0.7			39.3 ± 0.2	^[7]^[12]	[19,24]

Dietary fiber consists of two fractions (soluble and insoluble), and its properties are mainly determined by the proportion of these two fractions. Thus, soluble fiber is characterized by its ability to form viscous gels, in contact with water, in the intestinal tract. Insoluble fiber does not form gels in contact with water but is capable of retaining water in its structural matrix, producing an increase in fecal mass that accelerates intestinal transit. These differences in the behavior of the fibers in the intestinal transit result in different properties. Insoluble fiber is sparsely fermented and has a marked laxative and intestinal regulating effect, while soluble fiber is fermented in high proportion, and its main properties are related to the decrease of cholesterol and glucose in blood and the development of intestinal microbiota ^[17].

Algae are distinguished by the composition of the structural polysaccharides of the cell wall and reserve. Most of these polysaccharides can be considered as fiber, as they are not digested by human enzyme equipment, although some are degradable by enzymes produced by colonic bacteria ^[18]. The proportion of dietary fiber is considerable, ranging from 36% to 60% of its dry matter ^[19], with soluble dietary fiber being very high (approximately 55–70%) compared to terrestrial vegetables ^[20]. Within algae, the soluble fiber content is usually higher in red algae (15–22% dry weight) as in Chondrus and Porphyra (Nori) ^[21][22]. On the other hand, brown algae such as Fucus or Laminaria/Saccharina, have a higher insoluble fiber content (27–40% dry weight) ^[21][23].

Algae are distinguished by the composition of the structural polysaccharides of the cell wall and reserve. Most of these polysaccharides can be considered as fiber, as they are not digested by human enzyme equipment, although some are degradable by enzymes produced by colonic bacteria [30]. The proportion of dietary fiber is considerable, ranging from 36% to 60% of its dry matter [31], with soluble dietary fiber being very high (approximately 55–70%) compared to terrestrial vegetables [5]. Within algae, the soluble fiber content is usually higher in red algae (15–22% dry weight) as in Chondrus and Porphyra (Nori) [8,32]. On the other hand, brown algae such as Fucus or Laminaria/Saccharina, have a higher insoluble fiber content (27–40% dry weight) [8,33].

Table 2 presents the dietary fiber values of different algae. Seaweeds have a high proportion of soluble fiber ^[24][25], with an average content of 24.5 g/100 g and 21.8 g/100 g for insoluble fiber. Finally, the ratio fiber soluble/fiber insoluble (S/I) is greater than the values observed in terrestrial vegetables.

presents the dietary fiber values of different algae. Seaweeds have a high proportion of soluble fiber [34,35], with an average content of 24.5 g/100 g and 21.8 g/100 g for insoluble fiber. Finally, the ratio fiber soluble/fiber insoluble (S/I) is greater than the values observed in terrestrial vegetables.

Table 2.

Dietary fiber content in different algae (g/100 g).

	Seaweed			Soluble Fiber			Insoluble Fiber			Ref.
				Chlorophyta
			Chlorophyta

86]. In general, red algae have high EPA, palmitic acid, oleic acid, and arachidonic acid contents compared to brown algae, which contain high concentrations of oleic acid, linoleic acid and α-linolenic acid but low EPA. Green algae have in greater quantity linoleic acid and α-linolenic, palmitic, oleic and DHA [87,88]. Both red and brown algae are a source of omega-3 and omega-6 fatty acids [40,89]

Table 5

presents the proportion of EPA and DHA in algae and the relationship ω-6:ω-3.

Table 5.

Lipid content in different algae.

	Seaweed		Lipids g/100 g		EPA (%)
				Chlorophyta
Caulerpa lentillifera	Ulva lactuca
Caulerpa lentillifera	17.21 ± 0.87			15.78 ± 1.20	2.86 ± 0.04 (mg GAE/100 g DW) ^[26]	[36]
Enteromorpha spp.		17.2		16.2	^[27]	[37]
Ulva spp. (formerly Enteromorpha spp.)		21.9 ± 0.9		18.7 ± 2.1	^[3]	[15]
Ulva spp. (formerly Enteromorpha spp.)		20.53 ± 0.28		34.37 ± 0.7	^[4]	[16]
			Rhodophyta
Chondrus crispus		22.25 ± 0.99		12.04 ± 2.89	^[22]	[32]
Garateloupia turuturu		48.1 ± 1.0		12.3 ± 1.2	^[2]	[14]
Porphyra/Pyropia spp.		17.9		16.8	^[27]	[37]
			Phaeophyceae
Durvillaea antarctica		27.7 ± 1.2		43.7 ± 0.3	^[5]	[17]
Himanthalia elongata		23.63 ± 0.48		13.51 ± 0.45	^[6]	[18]
Himantalia elongata		25.7		7.0	^[27]	[37]
Saccharina latissima		17.12 ± 0.84		13.11 ± 0.56	^[6]	[18]
Sargassum fusiforme		32.9		16.3	^[27]	[37]
Undaria pinnatifida		30.0		5.3	^[27]	[37]

Marine algae, because they live in an environment with a very high concentration of salts, need to accumulate solutes that allow to regulate the osmotic balance between their cells and the environment. Many ions such as sodium, chlorine, and potassium are involved in this process, but certain low molecular weight carbohydrates are also involved ^[28]. These include, for example, sucrose in green algae, alditols such as mannitol in brown and red algae ^[28], and hexitols such as digeneasides and fluorosides in red algae ^[29]. In addition, the main low molecular weight carbohydrate present in many species of brown algae, especially in Laminaria and Ecklonia, is mannitol. Mannitol content is <10% of dry weight in Ascophyllyum nodosum and Laminaria hyperborea species, although it is also subject to many seasonal variations, reaching maximum levels of up to 25% of dry weight in autumn ^[21]. Finally, seaweeds also contain a high concentration of carbohydrates such as structural, storage, and functional polysaccharides, with values between 20% and 70%. However, they are not a good source of carbohydrates in terms of bioavailability ^[20] due to the high proportion of soluble dietary fiber between 55–70%.

The algae acquire from the marine environment, in which they live, a great wealth of mineral elements, being known for its high content of minerals between 8–40% of the dry weight of the seaweed (

Marine algae, because they live in an environment with a very high concentration of salts, need to accumulate solutes that allow to regulate the osmotic balance between their cells and the environment. Many ions such as sodium, chlorine, and potassium are involved in this process, but certain low molecular weight carbohydrates are also involved [38]. These include, for example, sucrose in green algae, alditols such as mannitol in brown and red algae [38], and hexitols such as digeneasides and fluorosides in red algae [39]. In addition, the main low molecular weight carbohydrate present in many species of brown algae, especially in Laminaria and Ecklonia, is mannitol. Mannitol content is <10% of dry weight in Ascophyllyum nodosum and Laminaria hyperborea species, although it is also subject to many seasonal variations, reaching maximum levels of up to 25% of dry weight in autumn [8]. Finally, seaweeds also contain a high concentration of carbohydrates such as structural, storage, and functional polysaccharides, with values between 20% and 70%. However, they are not a good source of carbohydrates in terms of bioavailability [5] due to the high proportion of soluble dietary fiber between 55–70%.

The algae acquire from the marine environment, in which they live, a great wealth of mineral elements, being known for its high content of minerals between 8–40% of the dry weight of the seaweed (

Table 3). They are worth highlighting the great abundance of essential minerals such as sodium, calcium, magnesium, potassium, chloride, sulfate, phosphorus, and micronutrients such as iodine, iron, zinc, copper, selenium, molybdenum, fluoride, manganese, boron, nickel, cobalt, etc. ^[16]. However, the mineral composition may vary depending on the taxonomic group, geographical, seasonal and physiological variations ^[30], and even with the type of processing and mineralization method applied ^[31]. Algae are a primary source of iodine, providing the daily iodine requirement (150 μg/day) ^[20]. Because of their high mineral content, algae can be used as a dietary supplement to help achieve the recommended daily amounts of some macro minerals and trace elements.

Algae, besides being an important source of minerals, are an excellent source of vitamins ^[32]. Algae, depending on their habitat, season, and species, vary in vitamin content, but almost all spend a lot of time exposed to direct sunlight in a watery environment. As a result, algae contain many forms of antioxidants, including vitamins and protective pigments. Seaweeds contain both water- and fat-soluble vitamins ^[33][34]. In this regard, algae are an excellent source of vitamins A, B1, B12, C, D, and E; riboflavin; niacin; pantothenic acid; and folic acid ^[32]. Water-soluble vitamins such as vitamin C are present in large amounts in laver (Porphyra umbilicalis), sea spaghetti (Himanthalia elongata), Crassiphycus changii (formerly Gracilaria changii) ^[35][36], and brown seaweed Ecklonia arborea (formerly Eisenia arborea) ^[37].

Algae also are a good source of B-group vitamins (particularly B1 and B12), as well as the lipophilic vitamin A (derived from β-carotene) and vitamin E (tocopherols) ^[38][39]. Finally, seaweed foods offer one of the few vegetarian alternatives for cobalamin (vitamin B12) in the diet. Cobalamin is not required or synthesized by higher plants ^[40], so fruits and vegetables are poor sources of vitamin B12, which explains why vitamin B12 deficiency is common among people following strict vegetarian or vegan diets ^[41][42][43].

). They are worth highlighting the great abundance of essential minerals such as sodium, calcium, magnesium, potassium, chloride, sulfate, phosphorus, and micronutrients such as iodine, iron, zinc, copper, selenium, molybdenum, fluoride, manganese, boron, nickel, cobalt, etc. [28]. However, the mineral composition may vary depending on the taxonomic group, geographical, seasonal and physiological variations [40], and even with the type of processing and mineralization method applied [41]. Algae are a primary source of iodine, providing the daily iodine requirement (150 μg/day) [5]. Because of their high mineral content, algae can be used as a dietary supplement to help achieve the recommended daily amounts of some macro minerals and trace elements.

Algae, besides being an important source of minerals, are an excellent source of vitamins [42]. Algae, depending on their habitat, season, and species, vary in vitamin content, but almost all spend a lot of time exposed to direct sunlight in a watery environment. As a result, algae contain many forms of antioxidants, including vitamins and protective pigments. Seaweeds contain both water- and fat-soluble vitamins [43,44]. In this regard, algae are an excellent source of vitamins A, B1, B12, C, D, and E; riboflavin; niacin; pantothenic acid; and folic acid [42]. Water-soluble vitamins such as vitamin C are present in large amounts in laver (Porphyra umbilicalis), sea spaghetti (Himanthalia elongata), Crassiphycus changii (formerly Gracilaria changii) [45,46], and brown seaweed Ecklonia arborea (formerly Eisenia arborea) [47].

Algae also are a good source of B-group vitamins (particularly B1 and B12), as well as the lipophilic vitamin A (derived from β-carotene) and vitamin E (tocopherols) [48,49]. Finally, seaweed foods offer one of the few vegetarian alternatives for cobalamin (vitamin B12) in the diet. Cobalamin is not required or synthesized by higher plants [50


		1.11 ± 0.05		^[73]	[83]
	0.86			-		^[26]	[36]				Rhodophyta
Codium fragile		1.5 ± 0.0			2.10 ± 0.00			-		^[39]	[49]	Ellisolandia elongata (formerly Corallina mediterranea)		37 (mg GAE/100 g extract)		^[45]	[55]
Crassiphycus birdiae		1.06 ± 0.07 (mg GAE/100 g extract)
Ulva lactuca		1.27 ± 0.11			0.87 ± 0.16			0.8 ± 0.01		^[5]	[17]	^[59]	[69]

					Rhodophyta										Jania rubens		56 (mg GAE/100 g extract)		^[45]	[55]
Agarophyton chilense		1.3 ± 0.0			1.30 ± 0.01			-		^[39]	[49]	Porphyra umbilicalis		5.53 (g GAE/100 g DW)		^[47]	[57]
Porphyra/Pyropia spp. (China)		1.0 ± 0.2			10.4 ± 7.46			-		^[7]^[39]	[19,49]		Pterocladiella capillacea (formerly Pterocladia capillacea)		200.0				1100.0			93 (mg GAE/100 g extract)		^[45]	[55		500.0			31.56	3.59	]		2.85	0.56	^[46]	[56]
					Phaeophyceae										Porphyra umbilicalis		687.0			1407.0			283.3						Phaeophyceae			1173.0
Ascophyllum nodosum		0.025		3.62 ± 0.17			7.24 ± 0.08			-		^[16		18.20			2.72			4.23			-		^[47]	[57]
^]		Pyropia tenera (formerly Porphyra tenera)		390.0			Alaria esculenta		2.80 ± 0.05 (mg GAE/100 g DW)		3500.0			565.0			3627.0		^[73]	[83]	-			10.30			2.72			2.21	<0.50	^[12]	[24]

Bifurcaria bifurcata		6.54 ± 0.27			4.09 ± 0.08			11.10 ± 1.13		^[16]	[28]	Pterocladiella capillacea (formerly Pterocladia capillacea)		6105.0			Ascophyllum nodosum	1495.0
Durvillaea antarctica		0.96 ± 0.03 g PGE/100 g extract					0.8 ± 0.1		^[74]	[84]		770.9			2949.5				-
	4.95 ± 0.11			1.66 ± 0.02			^[5]	[17]	22.70			3.33			4.21			0.43		^[45]	[55]
											Phaeophyceae
Bifurcaria bifurcata
Fucus vesiculosus		1.99 ± 0.23 g PGE/100 g extract		^[74]	Alaria esculenta		900.0	[56]
	[	28	]			[84]
	3.75 ± 0.20			9.94 ± 0.14			-		^[16]	[28]		Fucus vesiculosus		1.15 ± 0.02 g PGE/100 g extract
Himanthalia elongata			4400.0					<1.5		^[74]	[84]	700.0
	7.45			3900.0			-		^[47]	[57]	400.0			2.60			0.35			2.98			2.13		^[46]	[56]
Ascophyllum nodosum	Halopteris scoparia	984.7		328.7 ± 2.87 (mg GAE/100 g DW)
Laminaria spp.			3781.4		^[75]		1.0 ± 0.3	[85]	867.8			4575.7
	16.2 ± 8.9			-		-			^[7]	[19]	13.34			1.96			-			-		^[16]	[28]
Bifurcaria bifurcata		996.4			9316.3			528.0			1836.8			169.5			-			-			-			-		^[16]	[28]
Fucus vesiculosus		938.0			4322.0			994.0			5469.0			-			4.20			5.50			3.71			<0.50		^[12]	[24]
Himanthalia elongata		909.0			6739.0			826.6			3700.0			0.015			1.81			4.09			3.77			-		^[47]	[57]
Laminaria digitata		1005.0			11,579.0			659.0			3818.0			-			3.29			<0.50			1.77			<0.50		^[12]	[24]
Undaria pinnatifida		931.0			8699.0			1181.0			7064.0			-			7.56			0.87			1.74			<0.50		^[12]	[24]

The protein content of algae varies greatly between large groups of algae (brown, red and green). In brown algae, the protein content is generally low (5–24% of dry weight), while red and green algae have a higher protein content (10–47% of dry weight) [58]. As with other nutritional components of algae, the content of proteins, peptides, and amino acids is influenced by various factors, especially seasonal variation [8]. For example, brown algae Saccharina and Laminaria displayed the maximum protein content during the months of February to May [8]. A similar variation has been found in red algae species, with a maximum in summer and a considerable reduction during winter [58]. In general, algae proteins are rich in glycine, arginine, alanine, and glutamic acid; they contain essential amino acids at levels comparable to the requirements indicated by FAO/WHO. Their limiting amino acids are lysine and cystine [5,42]. Other amino acids present in algae are taurine, laminin, kainoids, kainic and domoic acids, and some mycosporin-type amino acids [59,60]. Taurine, in humans, participates in many physiological processes such as immunomodulation, membrane stabilization, ocular development, and the nervous system [61]. In addition, kainic and domoic acids are involved in the regulation of neurophysiological processes [62].

On the other hand, some studies have shown that phycobiliproteins extracted from red algae (phycoerythrin) could be beneficial in the prevention or treatment of neurodegenerative diseases caused by oxidative stress (Alzheimer and Parkinson’s) due to their antioxidant effects [63]. The lectins found in Bryothamnion spp. (Rhodophyta) show an inhibitory effect on the growth of strains of Steptococcus spp.; therefore, they can be used as bactericidal compounds [64]. Among the peptides found in algae, those with 2–20 amino acids abound. They can be linear, cyclic, depsipetides, or peptides with one or more amide bonds replaced by ester-kahalalides- bonds, dipeptides (carnosine, almazole D), tripeptides (glutathione), pentapetides (galaximide), hexapeptides, oligopeptides, and phycobiliproteins [65]. These isolated peptides are characterized by having antioxidant, antitumor, antiviral, antimicrobial, antihypertensive, anticoagulatory, and immunostimulatory activities [66]. In particular, the kahalalides P and Q present in green algae possess cytotoxic action on the HL-60 cell line, while the kahalalide F, isolated from Bryopsis spp. (Chlorophyta), reduces the density of non-metastatic prostate tumor cells [62]. The most abundant amino acids are lectins, phycobiliproteins, agglutinins, and glycoproteins [60].

The protein content of algae varies greatly between large groups of algae (brown, red and green). In brown algae, the protein content is generally low (5–24% of dry weight), while red and green algae have a higher protein content (10–47% of dry weight) ^[48]. As with other nutritional components of algae, the content of proteins, peptides, and amino acids is influenced by various factors, especially seasonal variation ^[21]. For example, brown algae Saccharina and Laminaria displayed the maximum protein content during the months of February to May ^[21]. A similar variation has been found in red algae species, with a maximum in summer and a considerable reduction during winter ^[48]. In general, algae proteins are rich in glycine, arginine, alanine, and glutamic acid; they contain essential amino acids at levels comparable to the requirements indicated by FAO/WHO. Their limiting amino acids are lysine and cystine ^[20][32]. Other amino acids present in algae are taurine, laminin, kainoids, kainic and domoic acids, and some mycosporin-type amino acids ^[49][50]. Taurine, in humans, participates in many physiological processes such as immunomodulation, membrane stabilization, ocular development, and the nervous system ^[51]. In addition, kainic and domoic acids are involved in the regulation of neurophysiological processes ^[52].

On the other hand, some studies have shown that phycobiliproteins extracted from red algae (phycoerythrin) could be beneficial in the prevention or treatment of neurodegenerative diseases caused by oxidative stress (Alzheimer and Parkinson’s) due to their antioxidant effects ^[53]. The lectins found in Bryothamnion spp. (Rhodophyta) show an inhibitory effect on the growth of strains of Steptococcus spp.; therefore, they can be used as bactericidal compounds ^[54]. Among the peptides found in algae, those with 2–20 amino acids abound. They can be linear, cyclic, depsipetides, or peptides with one or more amide bonds replaced by ester-kahalalides- bonds, dipeptides (carnosine, almazole D), tripeptides (glutathione), pentapetides (galaximide), hexapeptides, oligopeptides, and phycobiliproteins ^[55]. These isolated peptides are characterized by having antioxidant, antitumor, antiviral, antimicrobial, antihypertensive, anticoagulatory, and immunostimulatory activities ^[56]. In particular, the kahalalides P and Q present in green algae possess cytotoxic action on the HL-60 cell line, while the kahalalide F, isolated from Bryopsis spp. (Chlorophyta), reduces the density of non-metastatic prostate tumor cells ^[52]. The most abundant amino acids are lectins, phycobiliproteins, agglutinins, and glycoproteins ^[50].

3. Bioactive Compounds in Algae

Apart from their nutritional components, algae contain bioactive compounds with high antioxidant capacity, such as carotenoids and polyphenols ^{[5][57][58][59][60][61][62]}. The natural pigments of algae have been studied finding antioxidant, anticancer, anti-inflammatory (mainly based on modulating macrophage function) activity, among others ^[63]. Among the natural algae pigments stands out fucoxanthin, a carotenoid that is available in different species of brown algae ^[64]. In this regard, several authors ^{[65][66][67][68][69][70]} have shown that fucoxanthin from different types of algae have an antioxidant, anticancer, anti-inflammatory, anti-obesity, neuroprotective, photoprotective, and osteoporosis preventive effects ^{[62][65][66][67][68][69][70]}.

Polyphenols are a minority component of algae (

3. Bioactive Compounds in Algae

Apart from their nutritional components, algae contain bioactive compounds with high antioxidant capacity, such as carotenoids and polyphenols [17,67,68,69,70,71,72]. The natural pigments of algae have been studied finding antioxidant, anticancer, anti-inflammatory (mainly based on modulating macrophage function) activity, among others [73]. Among the natural algae pigments stands out fucoxanthin, a carotenoid that is available in different species of brown algae [74]. In this regard, several authors [75,76,77,78,79,80] have shown that fucoxanthin from different types of algae have an antioxidant, anticancer, anti-inflammatory, anti-obesity, neuroprotective, photoprotective, and osteoporosis preventive effects [72,75,76,77,78,79,80].

Polyphenols are a minority component of algae (

Table 4). Green and red algae contain low concentrations of polyphenols (<1% dry weight) compared to brown algae ^[22][30] and can reach up to 14% dry weight in Ascophyllum and Fucus genera ^[21]. Phlorotannins are the most widely described polyphenols of brown algae, especially in species of the genus Ecklonia ^[21][61], and are formed from phloroglucinol (1,3,5-trihydroxybenzene) oligomeric structures ^[71]. Phlorotannins can be found at concentrations of 20–250 mg/g dry weight in Ascophyllum nodosum, Fucus vesiculosus, Sargassum spinuligerum, and Cystophora retroflexa ^[72]. In addition to phlorotannins, other polyphenols have been described, such as fucol and its derivatives, flavonoids, and derivatives such as catechin and epicatechin ^[21].

). Green and red algae contain low concentrations of polyphenols (<1% dry weight) compared to brown algae [32,40] and can reach up to 14% dry weight in Ascophyllum and Fucus genera [8]. Phlorotannins are the most widely described polyphenols of brown algae, especially in species of the genus Ecklonia [8,71], and are formed from phloroglucinol (1,3,5-trihydroxybenzene) oligomeric structures [81]. Phlorotannins can be found at concentrations of 20–250 mg/g dry weight in Ascophyllum nodosum, Fucus vesiculosus, Sargassum spinuligerum, and

Himanthalia elongata

23.47 (g GAE/100 g DW)

⁴⁷

[

]

Macrocystis pyrifera

0.7 ± 0.1

0.47 ± 0.01

^[39]

[49]

Saccharina latissima

11.1 mg GAE/g DW

^[46]

Sargassum fusiforme

1.4 ± 0.1

42.4 ± 11.9

^[7]

[19]

Turbinaria conoides

Undaria pinnatifida

0.86 (mg GAE E/100 g DW)

^[57]

[67]

4.5 ± 0.7

13.2 ± 0.66

^[7]

Undaria pinnatifida

4.46 (g GAE/100 g DW)

^[47]

[57]

DW–dry weight; GAE–gallic acid equivalents; PGE–Phloroglucinol equivalents.

The lipid algae content is low (1–5%), with neutral lipids and glycolipids being the most abundant. The proportion of essential fatty acids in algae is higher than in terrestrial plants, because they synthesize long chain polyunsaturated fatty acids, highlighting the eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) that belong to the family of fatty acids ω-3 ^[76]. In general, red algae have high EPA, palmitic acid, oleic acid, and arachidonic acid contents compared to brown algae, which contain high concentrations of oleic acid, linoleic acid and α-linolenic acid but low EPA. Green algae have in greater quantity linoleic acid and α-linolenic, palmitic, oleic and DHA ^[77][78]. Both red and brown algae are a source of omega-3 and omega-6 fatty acids ^[30][79]

DW–dry weight; GAE–gallic acid equivalents; PGE–Phloroglucinol equivalents.

[

]

4. Biological Properties of Algae

The bioactive compounds present in seaweeds give them properties associated with the prevention and treatment of diseases (

4. Biological Properties of Algae

The bioactive compounds present in seaweeds give them properties associated with the prevention and treatment of diseases (

Figure 1), such as antidiabetic, antihypertensive, anti-inflammatory (based mainly on the modulation of macrophage function), antimicrobial, antitumor, antivirus, fat-lowering, and neuroprotective agents ^[63][80][81]. Primary and secondary metabolites can be also implicated in these applications. Primary metabolites are proteins, polysaccharides, and lipids involved in physiological functions. Among them, polysaccharides and fibers are the main compounds that display positive effects on chronic diseases such as cancer, cardiovascular diseases, diabetes, and obesity. On the other hand, secondary metabolites are minor molecules, such as phenolic compounds, halogenated compounds, sterols, terpenes, and small peptides, which are the result of stressful situations on seaweed tissues. Between them, exposure to ultraviolet radiation, changes in temperature and salinity, or environmental pollutants should be highlighted ^[82].

), such as antidiabetic, antihypertensive, anti-inflammatory (based mainly on the modulation of macrophage function), antimicrobial, antitumor, antivirus, fat-lowering, and neuroprotective agents [73,90,91]. Primary and secondary metabolites can be also implicated in these applications. Primary metabolites are proteins, polysaccharides, and lipids involved in physiological functions. Among them, polysaccharides and fibers are the main compounds that display positive effects on chronic diseases such as cancer, cardiovascular diseases, diabetes, and obesity. On the other hand, secondary metabolites are minor molecules, such as phenolic compounds, halogenated compounds, sterols, terpenes, and small peptides, which are the result of stressful situations on seaweed tissues. Between them, exposure to ultraviolet radiation, changes in temperature and salinity, or environmental pollutants should be highlighted [92].

Figure 1. Biological properties of seaweeds.

Biological properties of seaweeds.