Radical Depolymerization of Alginate Extracted from Moroccan Brown Seaweed Bifurcaria bifurcata

Bouissil Soukaina,Rchid Halima,El Alaoui-Talibi Zainab,Delattre Cédric,El Modafar Cherkaoui,Michaud Philippe,Pierre Guillaume

doi:10.3390/app10124166

Abstract

The degradation of alginate extracted from Moroccan Bifurcaria bifurcata has not been fully established to date. In this work, we report the extraction and the characterization of alginate (ASBB) from the brown algae B. bifurcata, as well as the production of oligo-alginates (OGABs) by using a green chemistry process. The depolymerization of ASBB was carried out by controlled radical hydrolysis through our green chemistry process using a hydrogen peroxide (H2O2) catalyst. The molecular weight (Mw) and degree of polymerization (DP) distribution of oligo-alginates (OGABs) obtained were then characterized by HPLC size exclusion chromatography (SEC) and high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Structural characterization revealed that after 6 h of depolymerization of ASBB, we obtained OGABs with Mw ≤ 5.5 kDa and 2 ≤ DP ≤ 24. These results highlight the effectiveness of the controlled radical hydrolysis of alginate to produce good yields of alginate fractions with controlled Mw with a known polymerization degree (DP) and without altering properties of oligo-alginates. Bifurcaria bifurcata can be a potential source of alginate and oligo-alginates given its abundance on the northwest Atlantic coast. The production and characterization of oligo-alginates promote their exploitation in the cosmetic, pharmaceutic, and agriculture fields.

Highlights

Among the main polysaccharides constituting brown algae, alginate represents 40% of their dry weight and it is mainly studied for its gelling properties [1]
The average molecular weight profile of oligo-alginates (OGABs) (Figure 2) ranged from 220,000 to 3500 g/mol after 10 h of radical depolymerization of ASBB. These results show a very large decrease in the Mw of the native alginate ASBB (220,000 g/mol) just after 2 h of hydrolysis
Algae polysaccharides were considered as a source of diverse oligosaccharide structures to the extent that oligosaccharides have demonstrated a role in many important industrial processes, such as brewing [25] and baking [26]

Summary

Introduction

Among the main polysaccharides constituting brown algae, alginate represents 40% of their dry weight and it is mainly studied for its gelling properties [1]. The existence of alginate in the form of alginic acid substituted with mineral salts, notably calcium, magnesium and sodium, gives the brown algae a strong and flexible appearance [2]. Alginate is a linear anionic copolymer formed from two monomers—α-L-guluronic acid (G) and β-D-mannuronic acid (M)—linked together by (β-1 → 4) link and organized as homo and/or heteropolymeric blocks (FMM /FGG and FMG blocks, respectively) [3]. About 30,000 tons of alginate are produced each year [4]. Alginate could be accounted as a copious resource for the development of biomaterials [5].

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