2009_Book_FoodChemistry

3.4 Phospho- and Glycolipids 181
(1,2-diacyl-3-(α-D-galactopyranosyl-1,6-β-D-galactopyranosyl)-L-glycerol)
6-O-acyl-MGDG and 6-0-acyl-DGDG are minor
components of plant lipids.
Sulfolipids are glyceroglycolipids which are
highly soluble in water since they contain a sugar
moiety esterified with sulfuric acid. The sugar
moiety is 6-sulfochinovose. Sulfolipids occur
in chloroplasts but are also detected in potato
tubers:
(sphingoglycolipid: ceramide-phosphate-sugar n ).
In the third group of sphingolipids the ceramide
moiety is linked by a phosphate residue to the
carbohydrate building blocks. These compounds
are also referred to as phytoglycolipids.
Sphingophospholipids. Sphingomyelin is one example
of a sphingophospholipid. It is the most
abundant sphingolipid and is found in myelin, the
fatty substance of the sheath around nerve fibers.
The structure of sphingomyelin is:
(3.35)
Sulfolipid(1,2-diacyl-(6-sulfo-α-D-chinovosyl-
1,3)-L-glycerol)
3.4.1.3 Sphingolipids
Sphingolipids contain sphingosine, an amino
alcohol with a long unsaturated hydrocarbon
chain (D-erythro-1,3-dihydroxy-2-amino-trans-
4-octadecene) instead of glycerol:
(3.36)
Sphingolipids which occur in plants, e. g., wheat,
contain phytosphingosines:
(3.37)
The amino group in sphingolipids is linked to
a fatty acid to form a carboxy amide, denoted as
ceramide. The primary hydroxyl group is either
esterified with phosphoric acid (sphingophospholipid:
ceramide-phosphate-base) or bound
glycosidically to a mono- di-, or oligosaccharide
(3.38)
Sphingoglycolipids are found in tissue of animal
origin, milk and in plants (especially cereals).
Based on structural properties of the carbohydrate
building blocks, one differentiates neutral
and acid glycosphingolipids. The sulfatides and
gangliosides also belong to this group.
Lactosylceramide in milk and the ceramide
glycosides of wheat are examples of neutral
glycosphingolipids that contain, next to glucose
and mannose, also saturated (14:0–28:0) and
monounsaturated (16:1–26:1) 2-hydroxy- or
2,3-dihydroxy fatty acids.
Formula 3.40 a depicts a sphingoglycolipid of
wheat.
Gangliosides contain sialic acid (N-acetylneuraminic
acid; cf. Formula 3.40 b). In the
ganglioside fraction of milk monosialosyllactosyl-ceramide
(cf. Formula 3.41) was
identified.
Phytosphingolipids. These lipids also have a complex
structure. Total hydrolysis yields phytosphingosine,
inositol, phosphoric acid and various
monosaccharides (galactose, arabinose, mannose,
glucosamine, glucuronic acid).
(3.39)