Brown seaweed species from Strangford Lough: compositional analyses of seaweed species and biostimulant formulations by rapid instrumental methods

Abstract

The aims of this study were to characterise the composition of five seaweed species (Ascophyllum nodosum, Fucus serratus, Fucus vesiculosus, Laminaria hyperborea and Sargassum muticum), their extracts and commercial formulations, using thermogravimetry (TGA), energy dispersive X-ray microanalysis (EDX), Fourier-transform infrared spectroscopy (FTIR) and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). Analyses of the samples by TGA and EDX provided information on the proportions of algal cell wall, inorganic fractions and minerals. The main carbohydrate constituents of the five species and extracts were identified by their pyrolysis products, e.g. 1-(2-furanyl) ethanone, 5-methyl-2-furcarboxaldehyde, 2-hydroxy-3-methyl-2-cyclopenten-1-one, diannhydromannitol, 1,6-anhydromannopyranose and 1,6-anhydromannofuranose, using Py-GC/MS. The differences in relative intensities of the infrared bands of the five species were enhanced, especially after acid extraction compared with alkaline or neutral treatments, resulting in improved understanding of the compositional changes. In addition four commercial formulations and two acidic extracts of A. nodosum were evaluated for composition using the techniques. The dry matter, pH, electrical conductivity, ash, carbon and nitrogen content of the six preparations showed significant differences in composition. Variations in fatty acid, alginic acid, mannitol, laminarin and fucoidan content of the six formulations were reported. The results have shown that TGA, EDX, Py-GC/MS and FTIR are complementary techniques for rapid evaluation of seaweed materials and products.