There is only few published data concerning vitamin content and bio-availability of vitamin forms contained in edible seaweeds. Generally, seaweeds contain both water- and fat-soluble vitamins, B-complex vitamins, vitamin C, provitamin A, and vitamin E, but some of them only in relatively low content.
The composition and therefore the vitamin profile of seaweeds vary and are affected by algal species, algal grown stage, geographic area and salinity, season of the year, availability of light, and temperature of sea water (Mabeau and Fleurence, 1993; Norziah and Ching, 2000).
The content of some vitamins in seaweeds, for example, vitamin B12 (Yamada et al., 1996a), varies greatly among samples of the same species. In many cases, light is an important regulator of vitamin biosynthesis;
thus plants growing in bright light have higher ascorbate content (Smith et al., 2007). Moreover, algae growing in the littoral zone or on the surface tend to have higher level of vitamin C than algae which is harvested from depth from 9 to 18 m (Norris et al., 1937). Further, other environmental parameters, such as concentration of certain compounds in the sea, can play the important role for vitamin occurrence in algae (Smith et al., 2007).
The importance of vitamins to plants themselves is often overlooked, but they play the essential roles in a plant metabolism too (Smith et al., 2007). Some algal species require different combinations of certain vitamins such as vitamins B12 and B1. Because the concentration of these vitamins in the natural environment is quite low, their absorption is insufficient (Croft et al., 2006). According to Yamada et al. (1996a), red algae Porphyra tenera can take up the free (not protein-bounded) form of vitamin B12 from the incubation medium by concentration- and temperature-dependent processes. The amount of uptake increases with the time of incubation.
Loss of vitamins can be induced by storage conditions such as the influence of light and oxygen. Moreover, there is a negative influence on a vitamin content caused by technological processing such as drying (sun-, oven-, freeze-drying) and sterilization, and culinary processes such as cooking, roasting, or baking, which could decline vitamin content due to water extrusion and high temperature during these procedures. This was observed, for example, in instable ascorbic acid (Norris et al., 1937).
According to the vitamin determination by Hernandez-Carmona et al. (2009), there are significant differences of certain vitamins content caused by seasonal variations, for example, in Eisenia arborea. It was observed that the highest content of some vitamins (A, B1, B2, and partly also vitamin C) was in spring opposite to the lowest spring value of vitamin E. Moreover, season was observed as the factor of carotenes content affection also in Palmaria. The highest content of carotenes was found in summer and the lowest in winter (L0vstad Holdt and Kraan, 2010).
Although certain macroalgae are rich in vitamins, the bioavailability of these compounds has not been studied sufficiently yet, so there is not enough data to clarify this problem for all vitamins satisfyingly. Bioavail-ability is influenced by several factors as follows: characteristics of the food source, location of the vitamin in the plant source, particle size, the presence of other influencing dietary components and interactions with other dietary factors, the type and extent of processing (Rock et al., 1998).
The bioavailability of vitamins is primarily related to solubility of each vitamin, which cohere with their intestinal absorption and therefore with their uptake by tissues as well. Bioavailability and absorption of some fat-soluble vitamins depend on whether they are consumed together with foodstuffs containing lipids or not. As being fat-soluble, these vitamins follow the same intestinal absorption path as dietary fat. Further, it is also important which of vitamin form is present in food. Therefore, for example, significant contributions to vitamin E activity are a- and g-tocopherols (Weber et al., 1997).
Although only little is known about the origin of vitamin B12 in the seaweeds, the bioavailability of algal vitamin B12 is quite contradictory. Generally, edible algae contain large amount of vitamin B12; some of them (e.g., Porphyra sp.) comprise a substantial amount of the form bioavailable to mammals. However, van den Berg et al. (1991) mentioned that at least part of the cobalamins may be analogues not bioavailable for humans as pseudo-B12. These compounds have adenosyl moiety instead of 5,6-dimethylbenzimidazole of the B12 molecule (Yamada et al., 1996b). Miyamoto et al. (2009) reports that dried purple laver (Porphyra sp.) could be well digested only under pH 2.0 conditions. Further, digestion rate of B12 would be estimated to be 50% in persons with normal gastric function.
It also appears that vitamins which are bound to fibers or some other carbohydrates in foods are not as available as the vitamins taken in the pure form. This is shown in seaweeds such as hijiki, which has a high percentage binding (42.7-45.6%) for thiamin. In contrast, kombu and susabi-nori showed the lowest binding for this vitamin (Suzuki etal., 1996).
It is said that 100 g of seaweed provides more than the daily requirements of vitamin A, B2, B12, and two-thirds of the vitamin C requirement (Ortiz et al., 2006). Most of the red seaweeds (Palmaria, Porphyra) contain large amounts of provitamin A and significant quantities of vitamins B1, B2, and B12, which are also present in green seaweeds. The vitamin content of brown seaweeds (Undaria, Laminaria) appears to be less remarkable, but brown seaweeds have high content of vitamin C (Mabeau and Fleurence, 1993). Some seaweed (such as Porphyra) can supply adequate amount of vitamin B12 in vegans.
The following summary is concerned with the most abundant seaweed vitamins which can sufficiently contribute to daily vitamin requirements, such as water-soluble vitamins B1, B2, B12, and C and fat-soluble provitamins A (p-carotene) and E. Because some results are given for fresh samples, some for dry ones, there is quite disputable to compare the data presented thereby.
Vitamin B1 and B2 are present in sufficient amount especially in brown and red marine algae. The highest amount of both vitamins was detected in wakame and kombu—0.3 and 0.24 mg B1/100 g dw; 1.35 and 0.85 mg
B2/100 g dw, respectively (Kolb et al., 2004). Lower levels of these vitamins are present in arame (0.06-0.12 and 0.65-0.92 mg/100 g dw, respectively), Caulerpa lentillifera and Ulva reticulata (Hernandez-Carmona et al., 2009; Ratana-Arporn and Chirapart, 2006). French Institut de Phytonutri-tion (FIP) describes much higher content of these vitamins, for example, in wakame—5 mg B1/100 g dw or 11.7 mg B2/100 g dw (MacArtain et al., 2007). 1 2
The intake of vitamin B12 in strict vegetarian and vegan diet is usually quite low. Therefore, this vitamin can easily become deficient. Lower levels of vitamin B12 in a diet may result in reduced levels of DNA methylation or elevated levels of homocysteine which is a risk factor for cardiovascular diseases (Hernandez et al., 2003). A particularly rich dietary source of the vitamin is seaweed, foods enriched with them or seaweed extracts, which are good alternate source of vitamin B12 for vegans. Thus consumption of some seaweed (nori) may keep vegans from suffering B12 deficiency (Suzuki, 1995). The highest content of vitamin B12 in seaweed is presented in red Porphyra sp. (nori)—133.8 mg B12/ 100 g dw, in the form active for human (Miyamoto et al., 2009). Other results of B12 content in this algae are present in range 12.02-68.8 mg/100 g dw (Takenaka et al., 2003; van den Berg et al., 1988; Watanabe et al., 1999, 2000). Further marine algae contain much less of B12; high content is found in green laver Enteromorpha sp., following by dulse, and low levels in Ulva sp., wakame, kombu, and hijiki (MacArtain et al., 2007; Watanabe et al., 1999; Yamada et al, 1996b).
Vitamin C is present especially in brown and green seaweeds, less in red algae. The highest levels of vitamin C were discovered in Enteromor-pha flexuosa and Ulva fasciata (300 and 220 mg/100 g dw, respectively) (McDermid and Stuercke, 2003). FIP states that the highest level of vitamin C is found in wakame (184.75 mg/100 g dw), red laver, and sea lettuce (MacArtain et al., 2007). Chan et al. (1997) determined the high content of vitamin C in freeze-dried algae Sargassum hemiphylum— 153.8 mg/100 g dw, smaller amount in oven- and sun-dried seaweed. Other seaweeds contain much less of vitamin C; high content is found in red algae Kappaphycus alvarezzi (107.1 mg/100 g dw) and low levels in arame, ogonori, Sargassum polycystum, Eucheuma cottonii, U. reticulata, and C. lentillifera (Fayaz et al., 2005; Hernandez-Carmona et al., 2009; Hong et al., 2007; Matanjun et al., 2009; Norziah and Ching, 2000; Ratana-Arporn and Chirapart, 2006).
Despite the low lipid content in seaweed, their fat contains high level of vitamin E. Generally, brown seaweeds contain more a-tocopherol (also p- and g-tocopherols) than red and green algae which contain only a-tocopherol. The highest amount of vitamin E was detected in kelp Macrocystis pyrifera, 132.77 mg/100 g fat (a-tocopherol), with total tocol content of 145.72 mg/100 g fat, and in Ulva lactuca with g-tocopherol value
96.35 mg/100 g fat (Ortiz et al, 2006, 2009), so compared to traditional plant oils, the fat of these seaweeds contain a high level of tocols. Moderate levels were found in Durvillaea antarctica (Ortiz et al., 2006). Low content of tocols was determined in Gracilaria chilensis, followed by S. polycystum, C. lentillifera, E. cottonii, and E. arborea (Hern^ndez-Carmona et al., 2009; Matanjun et al., 2009; Ortiz et al., 2009). FIP states that the highest level of vitamin E is in wakame and dulse (MacArtain et al., 2007).
Plant food such as algae does not contain intrinsic vitamin A, but its provitamins such as p-carotene. The high values of p-carotene with vitamin A activity were found in red seaweeds Gracilaria changgi, K. alvarezzi, and in brown algae kombu (5.2, 5.26, and 2.99 mg/100 g dw, respectively, recalculated to 865, 865, and 481 RE/100 g dw) (Fayaz et al., 2005; Kolb et al., 2004; Norziah and Ching, 2000). Moderate levels of vitamin A were determined in wakame, arame, sea grapes, and sea lettuce (Hernandez-Carmona et al., 2009; Ratana-Arporn and Chirapart, 2006).
D. Antioxidant activity of some vitamins contained in seaweed
Among the compounds found in seaweeds, those with antioxidant activity have an excellent potential for application in food industry and also in cosmetics and pharmacology industry, and for consumer interest too. Due to the presence of these compounds, marine algae may also have other health beneficial effects and therefore they could be used as nutra-ceuticals or in functional foodstuffs.
When seaweeds are exposed to a combination of light and high oxygen concentrations, the formation of free radicals and other oxidative reagents is induced. The absence of structural damage in the structural components suggests that seaweeds are able to generate the necessary compounds to protect themselves against oxidation (Jimenez-Escrig et al., 2001). Therefore, marine algae can be considered the important source of antioxidants. According to Tsuchihashi et al. (1995), the antioxidant potency is determined by several factors such as intrinsic chemical reactivity of antioxidant toward radical, site of generation and reactivity of the radicals, site of antioxidant, concentration and mobility of the antioxidant at the microenvironment, stability and fate of antioxidant-derived radical, and interaction with other antioxidants.
The compounds which are responsible for antioxidant activity in seaweed include vitamin E (a-tocopherol), carotenoids (p-carotene), and vitamin C (ascorbic acid), and partially vitamin B1 and niacin.
Oxidative forms, which arise in foodstuffs, are responsible for various free-radical-induced diseases such as cardiovascular diseases and certain types of cancers. Vitamins with a strong antioxidant capacity can be used as the first line therapeutic defense against cancer before cancer treatment (Simon, 2002).
The antioxidant activity of carotenoids is associated with its binding capacity with singlet oxygen by conjugated double bonds systems. The maximum protection is given by carotenoids with more than nine double bonds (Ribeiro et al., 2011). The effectiveness of carotenoids as antioxi-dants is also dependent upon their interaction with other coantioxidants, especially vitamins E and C. It was demonstrated that p-carotene is 32 times less reactive toward peroxyl radical than a-tocopherol and 11 times less reactive toward carbon-centered radical. Therefore, p-carotene is less potent as an antioxidant than a-tocopherol. Carotenoids may, however, lose their effectiveness as antioxidants at high concentration or at high partial pressures of oxygen. It is unlikely that carotenoids actually act as prooxidants in biological systems; they rather have a tendency to lose their effectiveness as antioxidants (Young and Lowe, 2001).
In certain experimental studies, there is an indication for the correlation between the diet rich in carotenoids (p-carotene) and a diminishing risk of cardiovascular diseases and some type of cancer—lung cancer, and probably also cancer of the esophagus, stomach, colon, rectum, breast, and cervix (Kohlmeier and Hastings, 1995; Krinsky, 1991). Presumably, they are capable of seeking for free radicals and neutralizing them and thus they inhibit cell proliferation (Simon, 2002).
Despite the low lipid content in seaweed, the presence of vitamin E is relevant as it acts as a strong antioxidant which prevents the formation of free radicals. a-Tocopherol, the most important member of tocol group, is capable of fixing free radicals via its phenol group in the structure and thus is considered to play an important role in oxidation of biological membranes, lipoproteins, and fat deposits, controlling or reducing lipid peroxidation (Sanchez-Machado et al., 2002).
It was discovered that vitamin E is associated with lower mortality from cerebrovascular diseases as this vitamin improves endothelial dysfunction and ameliorates vascular health and reduces vascular damage (Houston, 2005). There is also evidence that vitamin E may protect against cancer—the reduction in the risk of both lung and cervical cancers (Iso and Kubota, 2007; Simon, 2002). Vitamin E may protect against the development of cancer through several mechanisms such as reacting with genotoxic radicals, reducing mutagenic activity, inhibiting carcinogenic nitrosamine formation, protecting cell membranes against peroxidation, and/or enhancing the immune system (Weber et al., 1997).
Ascorbic acid inhibits the oxidation quite efficiently for a long period and also neutralizes free nitrites which are a substrate for carcinogens. Vitamin C acts as a potent synergist in the presence of a-tocopherol and spares this antioxidant.
It is believed that ascorbic acid prevents cancer by neutralizing free radicals before they can damage DNA and initiate tumor growth, or it may act as a prooxidant helping body's own free radicals to destroy tumors in their early stages (Naidu, 2003). It appears that there is a very strong relationship between vitamin C and the reduction of stomach cancer, and a possible relationship with the reduction of the risk of mouth, pharyngeal, lung, and gall bladder cancer in men (Iso and Kubota, 2007; Simon, 2002). The dietary intake of vitamin C is also inversely correlated with systolic and diastolic blood pressure as it reduces blood pressure in hypertensive patients, hyperlipidemics, and diabetics. Combination of vitamin C with other antioxidants (vitamin E, p-carotene) provides synergic antihypertensive effects (Houston, 2005).
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