Mr John LTerlabie CHEMICAL COMPOSITIONc ontd Most seeds have high LIPID content Except for certain fruits the occurrence of high lipids concentrations differentiates seeds from other plant organs ID: 700195
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Slide1
CHEMICAL COMPOSITION OF SEEDS
Mr. John
L.Terlabie
Slide2
CHEMICAL COMPOSITION...contd.
Most
seeds
have high
LIPID
content.
Except for certain fruits, the occurrence of high lipids concentrations differentiates seeds from other plant organs.
Lipids are concentrated in the endosperm or cotyledon storage tissues in Angiosperms.
Endosperm is generally solid.
Lipids provide the highest amount of potential energy per unit weight Slide3
CHEMICAL COMPOSITION...contd.
The seed lipid reserve is generally hydrolyzed
in situ
to glycerol and fatty acid by lipases.
The fatty acids are utilized for phospholipids and
glycolipids
.
These are required as constituents of organelles.
However, most are converted to sugars and transported to the seedling
(body)
for growth.Slide4
CHEMICAL COMPOSITION...contd.
They dissolve in organic solvents e.g. benzene, acetone, alcohol, ether but do not dissolve in H
2
O.
The value of seed-borne lipids for food and industrial uses is enormous.
In contrast to animal fats, their highly unsaturated chemical nature has caused increased interest in them for health purposes.
High lipid content is usually associated with decreased protein content e.g. soybean, rapeseed.Slide5
CHEMICAL COMPOSITION...contd.
All the basic protoplasmic components are present in seeds.
This include amino acid, vitamins, nucleic acid, co-enzymes and minerals.
Phosphorus content in most seeds is often very high. WHY?
This element occurs most commonly as
Phytin
-Salts
of
inositol
hexaphosphate
.Slide6
CHEMICAL COMPOSITION...contd.
All seed contain
PROTEIN
as the protoplasmic component.
Protein are huge N
2
containing molecules with huge structures, greater part of which yield amino acid upon hydrolysis of peptide bond.
They are so important to plant and animal life that all physiological reactions of living cells revolve around their physical and chemical properties and those of related compounds.Slide7
CHEMICAL COMPOSITION...contd.
Aside H
2
O, they are the principal components of all protoplasm of both plant and animal cells.
Seeds often contain unusual amino acids which are not constituents of proteins.
This may act as N
2
store and may be present to the extent of several percent of the seed’s dry weight.
Chlorophyll is absent in seeds.Slide8
CHEMICAL COMPOSITION...contd.
In some cases, e.g. legumes, large quantities of special reserved proteins with a distinctive chemical composition are also stored.
The storage proteins occur as membrane enveloped protein bodies (
Aleurone
bodies
)
They may occasionally occur as crystals.
The protein reserve in all cases is sufficient for growth before the plant becomes self-supporting.Slide9
CHEMICAL COMPOSITION...contd.
Seed storage proteins are less complex than protoplasmic protein and less likely to be tied up with lipids.
The great majority of seed protein are metabolically inactive and serve merely as food reserve for use by the growing embryo during germination.
Active ones are few but they are extremely important to the developing and germinating seed.
As enzyme, they catalyze the metabolic processes in digestion, translocation and utilization of stored food reserves; no growth can occur without them.Slide10
CHEMICAL COMPOSITION...contd.
CARBOHYDRATES
are the major storage substances in seeds.
Carbohydrates occur mainly as starch or
hemicellulose
.
Other carbohydrates that occur in non storage forms are
peptin
and mucilage.Slide11
CHEMICAL COMPOSITION...contd.
Starch is the principal and most wide spread storage carbohydrate.
They are metabolically inactive reserves stored until needed during germination.
Starch is stored in two related forms;
amylose
and
amylopeptin
which are two polymers of D-glucose.
Amylose
stains blue when exposed to iodine and its 100% digestible by alpha amylase.Slide12
CHEMICAL COMPOSITION...contd.
Amylopeptin
on the other hand is only about 50% digestible by alpha amylase and stains purplish-red when exposed to iodine.
However, they are both hydrolyzed by alpha and beta amylase during normal metabolism and germination.
Starch is stored as grains (up to 5µm in diameter) as formed in the
amyloplast
.
Hemicellulose
are normal cell wall components in all tissues.Slide13
CHEMICAL COMPOSITION...contd.
Hemicellulose
are usually found in the thickened
tertially
layers of cell walls of the endosperm or cotyledon instead of the interior region of the endosperm.
They are composed principally of
mannans
with small amount of glucose,
galactose
,
arabinose
as side chain on the main linear polymers of mannose residues.
Where
they form a major seed reserve, they are laid down as heavy cell wall thickening, which almost fill the lumen, as in seeds of the date palm-
Phoenix
dactylifera
.Slide14
Small amounts of soluble sugars are usually present.These sugars are concentrated mainly in the growing parts of the embryo i.e. shoot and root apices where meristematic
activities is highest.Slide15
CHEMICAL COMPOSITION...contd.
Water content is often very low ranging between 5-20% on a fresh weight basis compared to 80-90% of most plants in an active state.
This largely accounts for the very low metabolic rate in ungerminated seed.
Most of the water in dry seeds are firmly bound to
colloides
and inaccessible for hydrolytic reactions (not
unfreezable
).
This is only removable by temperature approaching 100
0
C or by storage in high vacuum.
Due to this dehydration, the cells and the
subcellular
organelles in dry seeds are often shrunken.Slide16
CHEMICAL COMPOSITION...contd.
Seeds also contain growth promoters, such as
cytokinin
, and
auxin
.
There is also the presence of growth inhibitors and most of them are
phenolic
compounds.
OTHER COMPOUNDS
:
Tannins
: Used for tanning process as found in cocoa.
Tannins contain
phenolic
and hydroxyl compounds.
Alkaloids
: Complex cyclic compounds containing N2.Slide17
CHEMICAL COMPOSITION...contd.
Most are white solids, however, nicotine is a liquid at room temperature.
Glucoside
Hormones:
Vitamin