Process Optimization and Properties Analysis of ι-Carrageenan via Homogeneous Extraction at Low Alkaline Concentration

Traditional heterogeneous extraction of ι-carrageenan (NaOH extraction of ι-carrageenan, NaOH-IC) has the problems of high alkali consumption and complicated process. In this study, an alternative homogeneous system was used to extract ι-carrageenan. The colloid was boiled out from Eucheuma spinosum and desulphurized under low-concentration KOH condition. After neutralized with CO₂, ι-carrageenan was obtained by alcohol precipitation (KOH extraction of ι-carrageenan, KOH-IC). The gel strength was used as the main evaluation index to optimize the extraction conditions of ι-carrageenan. As the optimized process conditions were KOH concentration 0.1 mol/L, alkali treatment time 5 h, reaction temperature 70 ℃, and material-liquid ratio 1:30 (w/v, g/mL), the ι-carrageenan gel strength reached 250.8 g/cm². Compared with the traditional process, KOH-IC exhibited lower sulfate content and viscosity. The solidification temperature and melting temperature of KOH-IC were 58.2 ℃ and 60.5 ℃, which were lower than those of NaOH-IC. The thermal decomposition temperature of KOH-IC was 275 ℃, which was significantly higher than that of NaOH-IC. The overall textural properties of KOH-IC were better than NaOH-IC, and their hardness, chewiness and adhesion results had significant differences (P<0.05). FT-IR analysis showed that compared with NaOH-IC, KOH-IC did not cause the generation of new absorption peaks. It indicated that different extraction processes do not lead to changes in the structure of ι-carrageenan. In sum, compared with the traditional heterogeneous extraction process, the ι-carrageenan product obtained from low concentration alkaline homogeneous extraction process has excellent overall textural properties. Furthermore, this new process has the advantages of easy operation and green extraction, and so on.