202 Marine Macro- and Microalgae: An Overview
Most naturally occurring phenolic compounds are associated with mono- or polysaccharides
(glycosides), linked to one or more of the phenolic groups. They may also occur as functional derivatives
such as esters and methyl esters. Phlorotannins (Fig. 4a), a group of phenolic compounds restricted to
polymers of phloroglucinol (1,3,5-trihydroxybenzene) (Fig. 4b), have been identified in several brown
algal families such as Alariaceae, Fucaceae, and Sargassaceae (Pavia and Brock 2000; Jormalainen and
Honkanen 2004). Some species of brown algae contain up to 20% of the phlorotannins in its dried form
(Koivikko et al. 2005; Koivikko et al. 2007). Phlorotannins purified from several different brown algae
have up to eight interconnected rings. Antioxidant activity is strongly related to the number of phenolic
rings present, which act as electron traps to scavenge peroxy, superoxide-anions, and hydroxyl radicals
(Athukorala et al. 2006; Balasundram et al. 2006).
Methanol extracts of marine brown algae are rich in phlorotannins, exhibiting inhibitory effects
on melanogenesis, and providing protection against photo-oxidative stress induced by UVB radiation
(Heo et al. 2010). Melanin, the major pigment responsible for the color of human skin, may be over
stimulated by chronic sun exposure or other hyperpigmentation diseases. Tyrosinase is a copper-containing
monooxygenase that catalyzes melanin synthesis in melanocytes (Kim et al. 2006) by hydroxylation of
tyrosine into dihydroxyphenylalanine (DOPA) and other intermediates (Heo et al. 2010). Phlorotannins
possess tyrosinase inhibitory activity due to their ability to complex the copper present in this enzyme.
Inhibition of tyrosinase activity can prevent melanogenesis. Overexposure to UV radiation causes an acute
sunburn reaction, clinically manifested as erythema. Chronic sun exposure is associated with abnormal
cutaneous reactions; that is, epidermal hyperplasia, accelerated breakdown of collagen, and inflammation.
Photo-oxidative stress has been directly linked to the onset of skin photodamage (Pillai et al. 2005). Hence,
regular skin treatment with products containing antioxidants is thought be a useful strategy for preventing/
reducing UV induced damage.
UVB radiation (280–320 nm) is highly oxidative and directly induces photodamage in skin cells by
overproduction of ROS that interact with cellular DNA, proteins and lipids to alter their cellular functions
(Heo et al. 2010). Brown algae are more tolerant to UVB radiation due to the presence of phlorotannins. The
inhibitory effect of phlorotannins on melanin synthesis (melanogenesis) and their protective effect against
photo-oxidative stress induced by UVB radiation were studied using three phlorotannins (phloroglucinol,
eckol, and dieckol) isolated from the brown algae, Ecklonia cava. The UVB radiation-induced DNA damage
in cultured human fibroblast cells was reported as 51.5%. However, the DNA damage was reduced by
the addition of phlorotannins to cells exposed to the UVB radiation (Balasundram et al. 2006). Dieckol
was found to be most potent phlorotannin in protecting the cells from UVB radiation by reducing the
DNA damage induced by UVB radiation (Ko et al. 2011). Dieckol (the hexamer of phloroglucinol) had
greater activity than eckol (trimer) and phloroglucinol (monomer). Dieckol (Fig. 5b) was found to inhibit
cellular pigmentation more effectively than kojic acid, a commercial tyrosinase inhibitor, but was much
less effective than retinol. Recent studies have demonstrated that the protective effect against oxidative
stress induced by ROS and UV radiation is connected to the number and position of hydrogen-donating
hydroxyl groups on the aromatic ring of the phenolic molecules. Therefore, as dieckol has more hydroxyl
groups than other phlorotannins, it would be the phlorotannin of choice for use as a natural antioxidant in
O
OH
OH
O
H
O
O
OH
O
H
OH
O
H
OH
OH
Fig. 4. The structure of: (a) phlorotannin; and (b) phloroglucinol.
(a)
(b)
Most naturally occurring phenolic compounds are associated with mono- or polysaccharides
(glycosides), linked to one or more of the phenolic groups. They may also occur as functional derivatives
such as esters and methyl esters. Phlorotannins (Fig. 4a), a group of phenolic compounds restricted to
polymers of phloroglucinol (1,3,5-trihydroxybenzene) (Fig. 4b), have been identified in several brown
algal families such as Alariaceae, Fucaceae, and Sargassaceae (Pavia and Brock 2000; Jormalainen and
Honkanen 2004). Some species of brown algae contain up to 20% of the phlorotannins in its dried form
(Koivikko et al. 2005; Koivikko et al. 2007). Phlorotannins purified from several different brown algae
have up to eight interconnected rings. Antioxidant activity is strongly related to the number of phenolic
rings present, which act as electron traps to scavenge peroxy, superoxide-anions, and hydroxyl radicals
(Athukorala et al. 2006; Balasundram et al. 2006).
Methanol extracts of marine brown algae are rich in phlorotannins, exhibiting inhibitory effects
on melanogenesis, and providing protection against photo-oxidative stress induced by UVB radiation
(Heo et al. 2010). Melanin, the major pigment responsible for the color of human skin, may be over
stimulated by chronic sun exposure or other hyperpigmentation diseases. Tyrosinase is a copper-containing
monooxygenase that catalyzes melanin synthesis in melanocytes (Kim et al. 2006) by hydroxylation of
tyrosine into dihydroxyphenylalanine (DOPA) and other intermediates (Heo et al. 2010). Phlorotannins
possess tyrosinase inhibitory activity due to their ability to complex the copper present in this enzyme.
Inhibition of tyrosinase activity can prevent melanogenesis. Overexposure to UV radiation causes an acute
sunburn reaction, clinically manifested as erythema. Chronic sun exposure is associated with abnormal
cutaneous reactions; that is, epidermal hyperplasia, accelerated breakdown of collagen, and inflammation.
Photo-oxidative stress has been directly linked to the onset of skin photodamage (Pillai et al. 2005). Hence,
regular skin treatment with products containing antioxidants is thought be a useful strategy for preventing/
reducing UV induced damage.
UVB radiation (280–320 nm) is highly oxidative and directly induces photodamage in skin cells by
overproduction of ROS that interact with cellular DNA, proteins and lipids to alter their cellular functions
(Heo et al. 2010). Brown algae are more tolerant to UVB radiation due to the presence of phlorotannins. The
inhibitory effect of phlorotannins on melanin synthesis (melanogenesis) and their protective effect against
photo-oxidative stress induced by UVB radiation were studied using three phlorotannins (phloroglucinol,
eckol, and dieckol) isolated from the brown algae, Ecklonia cava. The UVB radiation-induced DNA damage
in cultured human fibroblast cells was reported as 51.5%. However, the DNA damage was reduced by
the addition of phlorotannins to cells exposed to the UVB radiation (Balasundram et al. 2006). Dieckol
was found to be most potent phlorotannin in protecting the cells from UVB radiation by reducing the
DNA damage induced by UVB radiation (Ko et al. 2011). Dieckol (the hexamer of phloroglucinol) had
greater activity than eckol (trimer) and phloroglucinol (monomer). Dieckol (Fig. 5b) was found to inhibit
cellular pigmentation more effectively than kojic acid, a commercial tyrosinase inhibitor, but was much
less effective than retinol. Recent studies have demonstrated that the protective effect against oxidative
stress induced by ROS and UV radiation is connected to the number and position of hydrogen-donating
hydroxyl groups on the aromatic ring of the phenolic molecules. Therefore, as dieckol has more hydroxyl
groups than other phlorotannins, it would be the phlorotannin of choice for use as a natural antioxidant in
O
OH
OH
O
H
O
O
OH
O
H
OH
O
H
OH
OH
Fig. 4. The structure of: (a) phlorotannin; and (b) phloroglucinol.
(a)
(b)