Although in the last 250 years seaweeds have been used on
an industrial scale, first as a source of alkali for the soap and
glass industries, then as a source of iodine, and latterly for the
production of alginic acid, practically nothing was known of their
chemical composition and the effect of season and other influencing
factors on their composition.
In 1944 the Scottish Seaweed Research Association was formed
with the object of surveying the coast of Scotland to ascertain
if there was sufficient seaweed to justify the setting up of a large scale industry, studying the factors which influenced
composition and devising economical means of harvesting seaweed.
The surveys showed that only the brown seaweeds (Phaeophyceae)
occurred in sufficient quantity to warrant further investigation.
Consequently, a study was commenced on the factors likely to influence
their chemical composition.
FACTORS AFFECTING THE CHEMICAL COMPOSITION The effect of season and degree of exposure was first examined
for the three most commonly occurring sublittoral species. For a period of two years monthly samples of the Laminariaceae, Laminaria
cloustoni, L. digitata and L. saccharina, were collected, with the
L. digitata and the L. saccharina samples taken from two different
habitats to examine the effect of degree of exposure on chemical
composition. The samples were first analysed for moisture, total ash,
iodine, Kjeldahl nitrogen, mannitol, laminarin and alginic acid
and later for cellulose and combined L- fucose. This work was
continued for a further two years and, in addition, the seasonal
variation in the wet weight of the plants was studied. At the same
time samples of seawater were taken from above the weed beds and the
chemical composition of the seaweeds correlated with that of the
seawater in which they were growing.
The effect of depth of immersion on the chemical composition
of the Laminariaceae was also studied.
Monthly samples of the common littoral seaweeds, Fucus serratus,
F. vesiculosus, F. spiralis, Pelvetia canaliculata and Ascophyllum
nodosum were also taken, with A. nodostun collected from three different
habitats to determine the effect of degree of exposure on chemical
A study was carried out on the concentration gradients in
Laminaria saccharina fronds and it was shown that they do exist at
certain times of the year, contrary to the belief that such gradients
are not required in seaweeds of this type for the translocation of matter.
ISOLATION OF CHEMICALS FROM THE BROWN MAXINE ALGAE
As the seaweed industry in Britain is based solely on the
extraction of alginic acid, methods were worked out for the isolation
of the other constituents as by- products of the alginate process.
Employing these methods, quantities of mannitol, laminarin and fucoidin
were isolated and purified for studies which were being carried out by
collaborative investigators at a number of universities.
Laminarin and fucoidin were also considered as sources of
D- glucose and L- fucose respectively, and the optimum conditions for
the isolation of these sugars worked out. In view of an
increasing demand for the sugar D-galactose, different species of
red seaweeds were examined as possible sources, as well as indigenous
plant material such as bracken, heather, Sphagnum moss and peat.
In view of the commercial importance of alginic acid and the
belief that it could only be satisfactorily obtained from Laminaria
cloustoni stipes, an investigation was carried out to prove that it
can be isolated from any of the common brown seaweeds; variations
did occur, however, in the degree of polymerisation of the acids
isolated from different species.
As a result of the success of initial trials with sodium
laminarin sulphate as a blood anticoagulant, its preparation and that
of other possibly useful derivatives of laminarin were studied.
The use of charcoal columns in separating mixtures of salts,
mannitol, D-glucose and L-fucose, such as are obtained in seaweed
hydrolysates, was examined. The disaccharide, laminaribiose, was
isolated from a partial hydrolysate of laminarin on charcoal.
The possibility of preparing sex hormones from fucosterol,
which occurs in the brown seaweeds, was considered and a method for
its determination worked out and applied to samples of seaweed.
THE PRESERVATION OF SEAWEEDS
As the chemicals already discussed could probably be isolated
more cheaply from fresh seaweed, without the additional cost of drying,
methods of preserving fresh samples were studied and the chemical
changes which occur on ensiling were investigated.