Physicochemical properties of edible alginate film from Malaysian Sargassum polycystum C. Agardh

The edible brown seaweed, Sargassum polycystum was harvested from the coastal region of Malaysia. This study introduces the preparation of S. polycystum alginate through the external (protocol A) and internal (protocol B) gelation methods with 1% and 3% calcium chloride solutions. The physicochemical characteristics of the films such as transparency, internal viscosity, solubility, swelling index and chemical structure were studied. Results indicated that the films cross-linked with Ca2+ through Protocol A resulted in uneven films with rough surface compared to Protocol B that produced film with a uniform surface. Additionally, Protocol B with 0.5% glycerol produced films that was flexible and slightly soluble (7.11%) with the shape and integrity maintained. The H-1-NMR analysis estimated the mannuronic: guluronic (M: G) ratio of the film as 0.733 and thus, confirming the characteristics of the alginate gel as less viscous but rigid. Comparatively, the commercial alginate of the Laminarian species showed a lower M: G ratio of 0.351 that resulted in a highly viscous gel. Besides that, the FTIR analysis showed that glycerol at increasing concentrations reduces the intensity of the absorption band at 3451.0 cm(-1) (stretching vibrations of O-H). This indicated that the strong intermolecular bonds between the alginate polymer were reduced and thus, improved the flexibility of the films.