Validation of carrageenan production and characterisation from Hypnea sp.

Abstract

Marine red algae of the genus Hypnea are globally recognised for their ecological and economic significance. It is also renowned as a sustainable source of carrageenan, a sulphated polysaccharide with extensive applications in the food, pharmaceutical, and cosmetic industries. Accurate taxonomic identification of this species is crucial for optimising its utilisation and ensuring consistency in bioactive compound extraction. In the present study, the taxonomic identification of the collected Hypnea sp. was confirmed by comparison of the observed morphoanatomical characteristics with established taxonomic literature and through biochemical evidence, particularly the presence of carrageenan in the collected species. Observed morphological traits included the morphology, texture, and color of the thallus; shape of the holdfast; tip morphology; branching pattern; and thallus height. Anatomical characterisation focused on the arrangement of cortical and medullary cells and reproductive structures such as cystocarps. These features collectively confirmed the genus identity of the collected specimens. Carrageenan extraction, which served as the biochemical confirmation of genus identity, was conducted through hot NaOH treatment, aqueous re-dissolution, and ethanol precipitation. The process yielded 17.8±0.4% carrageenan, which aligns with reported seasonal variations in yield for Hypnea species (10 - 40%). The extracted carrageenan was characterised by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and by analysing the moisture content of the extract. The ATR-FTIR revealed distinct peaks at 928, 888, 847, and 767 cm-1, indicating the 3,6-anhydro-D-galactose, sulfate ester vibration, C–O–SO4 stretching at the C4 position of galactose, and a general vibration band for sulfated polysaccharides, respectively. These peaks closely match those of standard kappa carrageenan. Additionally, the moisture content of the dried carrageenan was determined to be 9.3±0.2%, consistent with previously reported values. The integration of morphological, anatomical, and biochemical evidence validates the taxonomic identity and biochemical potential of the specimens and underscores the biotechnological potential of Hypnea sp. for marine bioprospecting and natural product development.