54
Kulikova and Khotimchenko 2000; Vaśkovsky et al. 1996). However, PC is often
replaced with DGTS in green and its homologue, DGTA in brown seaweeds. PS
and PI are found in appreciable amounts, while DPG and PA are present as minor
components. A large number of unidentified lipids are also found in amounts ranging from 2.7 to 10.3% of PL (Dembitsky and Rozentsvet 1990; Dembitsky et al.
1990; Kulikova and Khotimchenko 2000). Glycerophospholipids are further characterized by higher contents of n-6 fatty acids (FAs) as compared to saccharolipids
except PG that has a substantial amount of n-3 FAs especially α-linolenic acid
(C18:3 n-3, ALA). Major FAs present are oleic (C18:1 n-9), palmitic (C16:0),
stearic acid (C18:0), arachidonic acid (C20:4 n-6, AA), and eicosapentaenoic acid
(C20:5 n-3, EPA). Further, an unusual FA, ∆3-trans-hexadecenoic acid (16:1, 3 t),
is esterified to sn-2 position of PG in all eukaryotic photosynthetic organisms
(Tremolieres and Siegenthaler 1998). Seaweed glycerophospholipids have numerous health- benefitting properties such as cognitive functions, anti-inflammatory
properties, and antitumor and anti-biological properties (Burri et al. 2012).
4.2.2 Saccharolipids
Saccharolipids also known as galactolipids and contain 1, 2-diacyl-sn-glycerol
moiety with mono- or oligosaccharide groups attached at sn-3 position of the
glycerol backbone. Seaweed saccharolipids mainly include monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and sulfolipid sulfoquinovosyldiacylglycerol (SQDG). MGDG and DGDG contain one and two
galactose molecules, respectively, and are uncharged at physiological pH, while
SQDG carries a negative charge due to its sulfonic acid residue at position 6 of
the monosaccharide moiety (Fig. 4.1). Saccharolipids are predominantly located
in photosynthetic membranes with MGDG and SQDG strictly restricted to the
thylakoid membranes of the chloroplast, while DGDG is also found in extraplastidial membranes. They constitute more than half of the lipids with MGDG
representing 31–56% (Sanina et al. 2004; Kumari et al. 2015; Yan et al. 2011),
with the exception of a few red algae (such as Palmaria stenogona Perestenko,
Ceramium kondoi Yendo, Laurencia nipponica Yamada, Ahnfeltia tobuchiensis
Kanno & Matsubara, and Exophyllum wentii Weber-van Bosse) where DGDG
content was higher (35.7–64% of polar lipids) and the members of Fucales
(brown seaweeds) contained higher SQDG (36.8–48.8%) (Khotimchenko 2002;
Sanina et al. 2004). A unique feature of these lipids is their high n-3 PUFA contents similar to higher plants. MGDG is the most unsaturated saccharolipid in
green and red seaweeds with DGDG in brown algae, while SQDG was the most
saturated one. MGDG and DGDG contain hexadecatetraenoic acid (C16:4 n-3),
ALA, stearidonic acid (C18:4 n-3, STA), and linoleic acid (C18:2 n-6, LA) in
green seaweeds, AA and EPA in red, and both in brown algae, while SQDG
contains palmitic and oleic acid as major FAs (Hofmann and Eichenberger
1997; Illijas et al. 2009; Khotimchenko 2002, 2003; Sanina et al. 2004).
P. Kumari
Kulikova and Khotimchenko 2000; Vaśkovsky et al. 1996). However, PC is often
replaced with DGTS in green and its homologue, DGTA in brown seaweeds. PS
and PI are found in appreciable amounts, while DPG and PA are present as minor
components. A large number of unidentified lipids are also found in amounts ranging from 2.7 to 10.3% of PL (Dembitsky and Rozentsvet 1990; Dembitsky et al.
1990; Kulikova and Khotimchenko 2000). Glycerophospholipids are further characterized by higher contents of n-6 fatty acids (FAs) as compared to saccharolipids
except PG that has a substantial amount of n-3 FAs especially α-linolenic acid
(C18:3 n-3, ALA). Major FAs present are oleic (C18:1 n-9), palmitic (C16:0),
stearic acid (C18:0), arachidonic acid (C20:4 n-6, AA), and eicosapentaenoic acid
(C20:5 n-3, EPA). Further, an unusual FA, ∆3-trans-hexadecenoic acid (16:1, 3 t),
is esterified to sn-2 position of PG in all eukaryotic photosynthetic organisms
(Tremolieres and Siegenthaler 1998). Seaweed glycerophospholipids have numerous health- benefitting properties such as cognitive functions, anti-inflammatory
properties, and antitumor and anti-biological properties (Burri et al. 2012).
4.2.2 Saccharolipids
Saccharolipids also known as galactolipids and contain 1, 2-diacyl-sn-glycerol
moiety with mono- or oligosaccharide groups attached at sn-3 position of the
glycerol backbone. Seaweed saccharolipids mainly include monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and sulfolipid sulfoquinovosyldiacylglycerol (SQDG). MGDG and DGDG contain one and two
galactose molecules, respectively, and are uncharged at physiological pH, while
SQDG carries a negative charge due to its sulfonic acid residue at position 6 of
the monosaccharide moiety (Fig. 4.1). Saccharolipids are predominantly located
in photosynthetic membranes with MGDG and SQDG strictly restricted to the
thylakoid membranes of the chloroplast, while DGDG is also found in extraplastidial membranes. They constitute more than half of the lipids with MGDG
representing 31–56% (Sanina et al. 2004; Kumari et al. 2015; Yan et al. 2011),
with the exception of a few red algae (such as Palmaria stenogona Perestenko,
Ceramium kondoi Yendo, Laurencia nipponica Yamada, Ahnfeltia tobuchiensis
Kanno & Matsubara, and Exophyllum wentii Weber-van Bosse) where DGDG
content was higher (35.7–64% of polar lipids) and the members of Fucales
(brown seaweeds) contained higher SQDG (36.8–48.8%) (Khotimchenko 2002;
Sanina et al. 2004). A unique feature of these lipids is their high n-3 PUFA contents similar to higher plants. MGDG is the most unsaturated saccharolipid in
green and red seaweeds with DGDG in brown algae, while SQDG was the most
saturated one. MGDG and DGDG contain hexadecatetraenoic acid (C16:4 n-3),
ALA, stearidonic acid (C18:4 n-3, STA), and linoleic acid (C18:2 n-6, LA) in
green seaweeds, AA and EPA in red, and both in brown algae, while SQDG
contains palmitic and oleic acid as major FAs (Hofmann and Eichenberger
1997; Illijas et al. 2009; Khotimchenko 2002, 2003; Sanina et al. 2004).
P. Kumari