Chemical Composition and Carbohydrate Characterization of Beach-Cast Marine Macrophytes from the Mexican Caribbean: Implications for Potential Bioethanol Production

Marine macrophytes are considered promising biomass for bioethanol production. The increases in anthropogenic nutrients and climate change have caused unprecedented blooming of 'sargasso' across the Atlantic since 2011. This biomass reaches the Caribbean Sea, stranding in large amounts along shorelines, and creating a serious waste management problem. The knowledge of its chemical composition is important to assess whether this material could serve as feedstock for third-generation bioethanol. The beach-cast marine macrophytes collected on the Mexican Caribbean coast in December 2018 were composed of brown seaweeds and a seagrass (23.5 and 76.5% relative abundance, respectively) including Sargassum fluitans, Sargassum natans I, Sargassum natans VIII, Turbinaria turbinata, and the angiosperm Syringodium filiforme. For valorization purposes, glucans, non-glucans carbohydrates and lignin were determined. Besides its abundance, underutilization, and low-cost this whole biomass may have potential as a promising raw material for third-generation bioethanol because it contains easily fermentable glucose such as mannitol (36.3% in whole biomass and 56% in the Sargassum species) and cellulose (36.3% on average). Other specific carbohydrates such as alginate (20-31%) and fucoidan (9.1-8.2%) were present in smaller amounts but they can also be converted to fermentable sugars with the proper methodology. Some advantages and limitations for the potential production of third-generation bioethanol from this biomass are discussed.