according to Stahl (Type 60 - Merck). The solvent system ethyl acetate (65
cm
3
)
and
35
cm
3
isopropanol-water mixture (2:1) was used. (Akhrem & Kuznetsova, 1965).
The chromatograms were run for three hours at 5°C. Spots were visualized by
spraying with acetonic-aniline-phthalate (aniline 2,0 cm
3
;
phthalic acid 3,0
g;
acetone
95
cm
3
and 5 cm
3
water) followed by heating at !05°C for
five
minutes. One
ul
of
either hydrolysate
of
known standard was applied to the base line
of
chromatogram.
The relative amounts present have been arbitrarily graded as
3+,
2+,
+,
(+)
or-,
according to the size and intensity
of
the spot obtained.
Nitrogen Content was determined by means
of
the conventional Kjeldahl method.
A conversion factor
of
6,25 was used for calculating the crude protein content.
RESULTS
AND
DISCUSSION
The crude protein content
of
the three investigated species
is
shown in Table
1.
In
all
three cases the crude protein content was unexpectedly high and compared favourably
with that
of
lucerne hay (17,1%) and was much higher than that of veld grass hay
(5,9%) (Van der Merwe, 1970)
According to Huneck (1973) the protein content
of
lichens varies between
1,6
and
11,4%
of
their dry weight. Some lichens, notably Peltigera canina growing in the
Himalayas may, however, contain as much as 21% protein (Subramanian
&
Ramakrishnan, 1964). The range
of
amino acids found
in
the investigated liches was
similar to those found in other plants and
micro~organisms,
and none
of
the less
commonly occurring amino acids were detected. (See table
2).
The highest
concentration
of
amino acid found was glutamic acid
in
the case of
P.
hottentotta.
There was a notable absence
of
cystine, hydroxy-proline and ornithine in
all
three
species. The absence
of
D-,
L-
or
meso-diaminopimelic acid
is
not unexpected as this
amino acid has so far only been found in bacterial
cell
walls. Unfortunately tryptophan
could not be resolved by the method used and no further attemps were made to
determine the tryptophan content
of
the lichen thalli.
The use
of
the factor
of
6,25 for converting Kjeldahl nitrogen into protein content,
is
subject to criticism, because no attempt was made to determine whether the ratio
between nitrogen from protein, free amino acids, nucleic acids or chlorophyll was
approximately the same as that from plant material
of
known cO,mposition.
The usefulness
of
a protein depends upon its digestibility as
well
as its biological
value. The biological value
is
determined by the number and kinds
of
amino acids
i present in the molecule: The nearer the food protein approaches the body proteins in
: amino acid make-up, the higher
will
be
the. biological value. (McDonald, Edwards &
j Greenhalgh, 1973). According to data on the essential amino acid composition
of
. proteins
for
n~n-ruminants
(NRC, 1973),
O.
convolutum was low in methionine/
; cystine, lysine, histidine and i-leucine;
P.
hottentotta was low in histidine, while
T.
capensis was low in histidine and phenylalanine/tyrosine. Unfortunately trypto-
phan, which
is,
an essential amino acid for non-ruminants, was not assayed. The uses
of
lichens by man as
an,
emergency ration and as part
of
his
daily diet has
i?een
39
Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2012)
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