Characterisation of alginate extracted from Saccharina latissima with deep eutectic solvents

This study evaluates the impact of using deep eutectic solvents (DES), specifically betaine-urea, as a novel extraction technology for alginate from brown seaweed and its effect on the techno-functionality of the final product. Ten eutectic mixtures were assessed, with betaine-urea (BU) demonstrating the highest performance, yielding 14.9 ± 2.0 % of the total amount of alginate in the first extraction step (BU-1). Although this yield was lower than the conventional acid-alkaline (AK) method (37.6 ± 4.1 %), a sequential extraction combining water (BU-2) and alkaline conditions (BU-3) achieved higher overall yields for the BU method. The study highlights significant differences in the chemical and rheological properties of alginates extracted with BU compared to those obtained via traditional methods. BU-extracted alginates exhibited the characteristic shear-thinning behaviour of alginate solutions but with markedly higher apparent viscosity at low shear rates. BU-2 displayed gel-like behaviour ( tan δ = 0.1) with a consistency index ( K ) 62 times higher than the acid-alkaline extract. Chemical analysis revealed a higher fraction of high-molecular-weight alginates in BU-2 and BU-3, partially explaining their increased viscosity. However, the role of betaine-urea in shaping the alginate structure and function should be further studied. This research underscores the potential of DES technology in enhancing the functionality of alginate, offering a potentially more sustainable alternative to mineral acid-base methods. • First report on alginate characterisation after extraction with betaine–urea DES. • Sequential DES strategy improved yield, purity, and functional alginate fractions. • DES-extracted alginate showed higher viscosity and gel-like behaviour in solution.