RELATIONSHIP BETWEEN CHEMICAL-PROPERTIES OF ALGINATE EXTRACTED FROM BROWN-ALGAE AND SODIUM-ION BINDING-CAPACITY IN-VITRO

Alginic acid has a physiological function to promote the excretion of sodium ion. As the chemical structure is known to affect the function of alginic acid as a dietary fibre and also the affinity for ions to a great extent, it is necessary to clarify the effect of the chemical p roperties on the sodium ion binding capacity in order to establish the extraction conditions and origins of alginic acid having higher bindi ng capacity. In the present investigation, alginic acid (H-Alg) and po tassium alginate (K-Alg) were extracted from Laminaria japonica Aresch oung, Ecklonia cava Kjellman and Sargassum hemiphyllum under different acid hydrolysis conditions, and the relationship between the sodium i on binding capacity in vitro and the chemical properties such as the c omposition and sequence of uronic acid and the molecular weight were e xamined. The ratio of D-mannuronic acid to L-guluronic acid (M/G ratio ) and the molecular weight of K-Alg prepared in this study were in the range of 0.3 to 1.2 and 1.5 x 10(4) to more than 15 x 10(4) depending on the species of brown algae and the extraction conditions, respecti vely. In spite of such a large variation of the chemical properties, n o significant difference was observed in the sodium ion binding capaci ty, suggesting that the sodium ion binding capacity does not depend on those chemical properties. It was noteworthy that K-Alg from S, hemip hyllum had a much lower M/G ratio (0.3 similar to 0.4) and a higher pe rcentage of homopolymeric blocks of L-guluronic acid than that from th e others, while the yield and the sodium ion binding capacity were equ ivalent. As the homopolymeric blocks of L-guluronic acid were less sus ceptible to enterobacteria than the homopolymeric blocks of D-mannuron ic acid, S. hemiphyllum may be a promising bioresourse for the extract ion of alginate that can have higher capacity to excrete sodium ion.