Composition and block structure of alginates from New Zealand brown seaweeds

Alginates have been extracted from seven brown algae found in the Southern Hemisphere and characterized by H-1 and C-13 NMR analyses. The results are compared with similar analyses obtained in this work for three commercially available alginates isolated from Macrocystis pyrifera, a species of the Northern Hemisphere. Overall the ten alginates display a wide range of compositions, ranging from the very high mannuronic acid containing alginate extracted from Durvillaea antarctica (F-M = 0.80) to the moderately high guluronic acid containing alginate from Marginariella boryana (F-G = 0.56). All data are examined in terms of two addition copolymerization models, namely the Bemoullian and the first-order Markov models. Monomer distributions in the high M and intermediate composition alginates have M-diad frequencies calculated from the NMR analyses that agree closely with Bernoullian distributions, the best agreements being obtained for those alginates in which F-M is greater than 0.72. However, as the monomer composition tends towards a higher G content, both of the above statistical models fail to satisfactorily describe the distributions of either the M or the G residues. A feature of this work is the excellent agreement obtained for the H-1 and the C-13 NMR analyses. (C) 1996 Elsevier Science Ltd.