Multicomponent fractionation of Saccharina latissima brown algae using chelating salt solutions

Abstract

A fractionation strategy for Saccharina latissima algal biomass was developed utilizing chelating extraction salt solutions to mediate the liberation of algal components. Alginate, cellulose, laminarin, mannitol, protein, and inorganic salts were quantified in the fractions to reveal their individual dissolution patterns. Chelation power was identified as a key parameter for liberating alginate and increasing the yield of extracted components. The most efficient fractionation was achieved using aqueous sodium citrate as the extraction solution, producing an alginate-rich soluble fraction and a salt-poor insoluble fraction rich in cellulose and protein. Extractions at decreased pH were shown to be beneficial because they decreased the M/G ratio of the extracted alginate and concentrated the protein in the insoluble fraction from which it can easily be recovered; these effects could be achieved by switching the traditional sodium carbonate extraction solution with salts that have chelation capacity at lower pH. A cyclic extraction demonstrated that the sodium citrate solution can be reused for multiple alginate extractions with the buildup of the concentrations of other valuable components in the solution.

Keywords: Alginate; Chelation; Extraction; Fractionation; Kelp; Saccharina latissima.

Fig. 1

Experimental figure for the chelation driven fractionation of Saccharina latissima yielding an insoluble fraction (XI) and a soluble fraction (XII), which was subsequently precipitated by CaCl₂ (XVI)

Fig. 2

Yields of the insoluble fraction (light gray) and precipitated fraction (dark gray) after extraction with various solutions. Error bars are calculated as the T-distribution (95 %) confidence intervals

Fig. 3

¹H NMR spectra of precipitated fractions (Fig. 1, step XVI) using sodium citrate (I), sodium oxalate (II), sodium carbonate (III), sodium hydroxide (IV), and commercial alginic acid (V). The integrated peak areas a, b, and c were calculated between 5.02–4.88 ppm, 4.63–4.49 ppm, and 4.45–4.27 ppm, with a baseline between the start and the end point of integration as the lower constraint for the integration areas

Fig. 4

Relative contents of glucose (dark gray), mannuronic acid (light gray), and guluronic acid (white) in the insoluble fractions (Fig. 1, step VIII)

Fig. 5

Alginate (light gray) and ash (dark gray) contents of the insoluble fractions and Ca²⁺ ion association constants of the anions in each extraction solution (circles), which follows the logarithmic scale to the right