Characterization of high value products in the side-stream of Laminaria hyperborea alginate production - Targeting the phenolic content

Abstract

Sustainable production based on renewable biomass and efficient bioprocesses are important elements in the growing blue bioeconomy. The traditional Laminaria hyperborea alginate production disposes approximately 80 % of the raw material, ignoring large amounts of potential high-value products from the alga. Particularly, the leaf fraction of the seaweed is often disregarded. This study aimed to characterize high value products from the alginate production side-stream – focusing on the leaf biomass and particularly targeting the phenolic content. After extraction and solvent optimization, 60 % methanol was used for the extraction. The extract was further purified with PuriFlash and semi-preparative chromatography and increasing phenolic selectivity and purity was observed with TPC and qNMR, as well as antioxidant activity (ORAC). In the purified fractions, the LR LC-MS analyses displayed several masses, where 96 % (n = 1376) were of lower molecular weights (< 800 Da). Fifteen high value compounds were further identified using HR LC-MS (MS/MS) and/or NMR. This also included non-phenolics such as fucoxanthin, aliphatic acids and mannitol. Nonetheless, most compounds were identified as the targeted phenolics, consisting of lower molecular weight phenolic acids (salicylic acid, veratric acid, 5-caboxyvanillic acid, sinapic acid, 5-sulfosalicylic acid, vanillic acid 4-sulfate, and dihydrocaffeic acid 3-sulfate) and phlorotannins (trimer, tetramer, hexamer, and a sulfated dimer). None of the identified phenolics have previously been reported in L. hyperborea. In general, a high occurrence of sulfated phenolic compounds was observed and a sulfated diphlorethol/difucol was characterized for the first time. The isolation and characterization of high value components in the leaf biomass of L. hyperborea strongly supports the development of a total utilization of commercial alginate production. The characterization also adds information on the phenolic content of seaweeds at a molecular level, valuable to research on seaweed biosynthesis and development, chemical ecology, and ocean monitoring.