Structural and chemical properties of kappa-carrageenan extracted from macroalgae by deep eutectic solvents and sustainable biopolymer films produced thereof

The red macroalga Kappaphycus alvarezii serves as a primary source of kappa-carrageenan, a compound with broad potential in various practical applications. Kappa-carrageenan was isolated from this red macroalga using deep eutectic solvents (DES) composed of choline chloride combined with glycerol, ethylene glycol, and urea in a molar ratio of 1:2, along with 30 % added water. The extracted kappa-carrageenan was analyzed based on yield, chemical composition, structural, morphological, elemental, and thermal characteristics. Herein, the glycerol-based DES yielded extracts with superior properties in most evaluated parameters. The optimal film properties were achieved using kappa-carrageenan extracted with the choline chloride - glycerol DES, demonstrating a mechanical strength of 28.63 ± 0.79 MPa and a water contact angle of 76.93° ± 0.41. These findings suggest that the hydrated choline chloride-based DES provides an effective method for isolating kappa-carrageenan from Kappaphycus alvarezii, with the resulting extracts showing potential as sustainable marine-derived biomaterials for packaging applications.