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Title: A study of the constituents of the brown marine algae
Author: Black, W. A. P.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1956
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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 composition. 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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.Sc.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available