Thermochemical characterization of brown seaweed, Laminaria digitata from UK shores

Brown algae, Laminaria digitata samples were collected over six-month intervals within a year (January, July and December 2015) and assessed for a range of thermochemical properties. Initial pyrolysis rates using thermo-gravimetric analysis (TGA) were carried out to assess their proximate characteristics, ranging from moisture content (MC) (3.48%-4.10%), volatile content (VC) (56.64-56.23%), char (11.80-12.76%) and fixed carbon (27.87-29.95%). Analysis by pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) identified sixty four compounds present in all samples, twenty which have been previously reported as major pyrolysis products of Laminaria digitata. H-1 NMR analysis of sodium alginate fractions extracted from the samples was used to characterise the monad, diad, triad frequencies and average block length of the alginate. Results of the monad frequencies F-M (0.36-0.46) and F-G (0.54-0.64) are consistent with reported values in literature. The Laminaria digitata alginate also showed values that are in agreement with most reported literature for both diad frequencies, homopolymeric mannuronic (F-GG = 0.19-0.25) and guluronic (F-MM = 0.33-0.47) blocks with alternating block fractions of (F-GM = 0.17-0.21) and (F-MG = 0.17-0.21), respectively. The M/G ratio value of 1.171.80 has been stated for alginates that can be used to produce soft and elastic gels rather than brittle ones. Furthermore, the computed triad frequencies results are (F-GGG = 0.14-0.17, F-MGM = 0.11-0.13, F-GGM = F-MGG = 0.05-0.09) and the average block lengths are (N-G = 2.15-2.22 and N-M = 2.61-3.85).