Microstructural and carbohydrate compositional changes induced by enzymatic saccharification of green seaweed from West Africa

The use of marine macroalgae as carbon source for fermentation is gaining increasing attention due to their high carbohydrate content and availability. Three green seaweed species Chaetomorpha linum, Ulva fasciata and Caulerpa taxifolia were investigated for their amenability to enzymatic saccharification. Microstructural changes were studied in order to understand the physical changes occurring in the seaweeds during saccarification and to identify structural barriers. C. linum had highest glucan content (20%), compared to 16% in U. fasciata and 6% in C. taxifolia indicating large differences in composition. Glucose yields obtained after 24 h of enzymatic saccharification were 59, 38 and 60% for C. taxifolia, U. fasciata and C. linum, respectively, based on the glucan content. Pre-autoclaving increased the saccharification yield to 81, 99 and 71%, respectively. Morphologically, C. linum displayed unbranched filaments, U. fasciata two-cell layer large sheets and C. taxifolia featured leaf like structures. Enzymatic saccharification resulted in cell wall degradation and release of the chlorophyll content in C. linum, delamination of sheets in U. fasciata and surface erosion of leaves in C. taxifolia. C. taxifolia deviated in being very rich in β-1,3 linked xylan (46%), which was only hydrolysed at 1% xylose yield due to lack of β-1,3-xylanase. Based on the high cellulose content and no need for pre-treatment C. linum was the best source of glucose among the three types of green seaweed species. Further studies are warranted to assess fermentation. We also conclude that for C. taxifolia enzymatic saccharification with β-1,3-xylanase might enable further xylose release than obtained here with the enzymatic cellulase treatment.