The quantity of alginic acid in the Adriatic brown algae

Abstract

      The amount of alginic acid in some Adriatic brown algae was determined by different methods.

      Both manometric and potentiometric determinations of the carbon dioxide, evolved during decarboxylation with acid, were used. Further, the gravimetric and Ca-acetate methods were adapted.

      It became obvious that the results obtained manometrically, were generally high. The values obtained by other methods did not too agree with each other in all the cases.

      The results indicated that Laminaria rodriguezii, with 30 g alginic acid per 100 g dry matter, had the highest amount among the material investigated.

     The amount of alginic add, being rather high in the Fucaceae, Cladostephus verticillatus and Colpomenia sinuosa, was considerably lower in the Dictyotaceae and the species Halopteris scoparia.

      The amount of uronic acids in the isolated products were estimated by means of the Ca-acetate method. It became evident, that other substances, besides alginic acid, were extracted with alkali.

     As obvious from table II., the data obtained by means of the Ca-acetate method are considerably higher than those obtained gravimetrically, if the correction for the uronic acid contents in the isolated products was taken into account. This fact is true for all the material investigated, with the exception of Laminaria rodriguezii.

     Measurements of the relative viscosity of the Na- alginates obtained indica­ted that it was about 10 times higher in Laminaria rodriguezii than in the rest of the material. One might assume that the alginates in question are of a lower molecular weight than the one obtained from Laminaria rodriguezii. It might be possible, too, that some of the low molecular poliuronates were lost during the isolation process, while they can be determined, if the Ca-acetate method is applied directly on the algal tissue.

       The alginate obtained from Laminaria rodriguezii had a high relative visco­sity, and was tread-like and of white colour. The rest of the alginates obtained were of a rather low relative viscosity and of a brown colour. Their production should then involve a bleaching process.

       Previous investigations of the seasonal variations of the alginic add con­tents in Adriatic brown algae (Munda, 1962) indicated that the latter was higher in the branches of the Cystoseirae than in their perennial basal parts. Finally, a negative correlation with their ash content was established.