Acid depolymerization of cell wall polysaccharides from Ulvan-rich extracts of green seaweeds

Abstract

There is an emerging interest for marine biomass resources due to its unique and complex structures which serve as renewable sources for chemicals and poly¬mers into a wide variety of applications. Seaweed polysaccharides (fucoidan, carrageenan, alginate, agar-agar, ulvan, etc) are bioactive compounds with therapeutic applications (i.e. antiviral activity, immuno-inflammatory or anti¬tumoral among others). Ulvan is a structural sulfated polysaccharide from the cell walls of Ulva spp green seaweed (Chlorophyta) that contains mainly two types of disaccharides, ulvanobiuronic 3-sulfate type A and ulvanobiouronic 3-sulfate type B; containing L-rhamnose, D-glucose and D-xylose as sugars and D-glucuronic and L-iduronic as uronic acids (Tako et al., 2015) and represents about 8-29% of Ulva spp total dry weight. Ulvan can form thermoreversible gels, exfoliated complexes with clays, and its demonstrated biological properties are valuable form agricultural, food and pharmaceutical applications (Cunha & Grenha, 2016). However, there is not a clear consensus regarding adequate ulvan composition or analytical procedures. Therefore, the exact chemical structure and composition as well as the molecular weight of ulvan is not well-known (Pankiewicz et al., 2016). These parameters directly affect the biological activity and the physic-chemical properties of the different ulvans isolated from Ulva spp seaweed cell-wall which is crucial for meeting the required specifications of each final application (tissue engineering, skin care, pre-biotics, etc) of the different potential markets (cosmetics, nutraceutics, pharmaceutics). In order to study the chemical composition of ulvan, different depolymerization methods can be used. Most widely used in the literature for ulvan-rich extracts depolymeriza¬tion is methanolysis (Costa et al., 2012; Pezoa-Conte et al., 2015). Nevertheless, in a previous study, authors studied three different methods for depolymeriza¬tion of Ulvan-rich extracts from Ulva rigida (methanolysis, mild acid hydrolysis -hydrochloric acid- and strong acid hydrolysis- sulfuric acid) and the highest sugar conversion was observed under mild acid hydrolysis (Macías et al., 2019). For this reason, the main goal of this research is to study the acid depolymer¬ization of the cell-wall polysaccharides of Ulva rigida with hcl under different conditions and the quantitative analysis of the neutral and acidic monomers.