Preparation of low-molecular weight alginic acid by acid hydrolysis

Three kinds of low-molecular weight alginic acid fractions, Alg.A, B, and C, were prepared from a commercial alginic acid by acid hydrolysis using phosphoric acid. Alg.A was obtained as an insoluble fraction by the filtration of mixture. Alg.B was obtained as a precipitate by pouring the filtered solution into water. Alg.C was obtained as a precipitate by pouring the filtrate into methanol. Measurements with 13C NMR, GPC and WAXS were performed on the prepared fractions for characterization. Alg.A was composed of rich M and G blocks, and had DPn and DPw/DPn values of 79 and 3.11, respectively. Alg.B was mainly composed of M block, and had DPn and DPw/DPn values of 38 and 2.57, respectively. Alg.C had a random structure including many alternating sequences, and had DPn and DPw/DPn values of 35 and 2.11, respectively. Alginic acid oligomers prepared in this study, Alg.B and C, were improved regarding in solubility in water and the viscosity of their aqueous solution.