Tailoring κ/ι-hybrid carrageenans from red algae Chondracanthus chamissoi via alkaline pretreatment: characterization and potential applications in vanilla custard preparation and methylene blue removal.

The valorization of algal-derived biomass has attracted considerable interest, since several metric tons of this marine biomass accumulate on beaches along the northern and southern coasts of Peru. In this context, this study explores the potential use of Chondracanthus chamissoi as a source of carrageenans tailored for specific applications. The seaweed was pretreated with a mixture of KCl and alkaline hydroxides, including a reference sample pretreated with H₂O. Subsequently, carrageenan was extracted under reflux at 90-95 °C for 4 h, followed by ethanol precipitation and lyophilization. Structural elucidation by FT-IR analysis showed the characteristic κ-carrageenan bands at 1219 cm-1 (S=O), 925 cm-1, and 843 cm-1, along with a distinctive band of ι-carrageenan at 804 cm-1. In complement, 1H NMR analyses revealed the presence of κ/ι-hybrid carrageenans containing approximately 67% and 33% of κ- and ι-units, respectively. Furthermore, 13C CP/MAS NMR spectra confirmed the absence of impurities such as pyruvates. Morphological evaluation by FESEM revealed flake-like structures, while EDX elemental mapping showed a higher density of oxygen atoms in the carrageenan extracted from KCl/KOH pretreated algae. Regarding rheological behavior, algae pretreatment with Ca(OH)2 favored shear-thinning behavior of carrageenans. Therefore, the obtained carrageenans were used to prepare vanilla custard desserts and mechanically evaluated under a uniaxial compression test. Finally, seaweed pretreatment with KOH significantly enhanced the mechanical properties of carrageenan hydrogels. These materials were functionalized by immersion in a KCl/chitosan solution and their ability to remove methylene blue from aqueous media was evaluated.