Improving hybrid carrageenan gel properties and extraction efficiency from mastocarpus stellatus and chondrus crispus with subcritical water

This study aimed to optimize the extraction of carrageenan from two species of red macroalgae, false Irish moss (Mastocarpus stellatus Stackhouse Guiry) and Irish moss (Chondrus crispus Stackhouse) using subcritical water extraction (SWE). A central composite factorial design was applied to evaluate the influence of temperature (90- 160 ºC) and pressure (40-90 bar), keeping extraction time and solid-to-liquid ratio constant, i.e., 30 min and 1:30 g/mL (w/v), on two responses: carrageenan yield (%) and gel capacity. For each species, 13 different SWE conditions were performed. These extracts were then compared to those obtained through conventional extraction performed with water (3h at 80 ºC + 1h at 90 ºC). All extracts were characterized based on their yield, gelling capacity, and gels rheological characteristics The carrageenan yields from M. stellatus ranged from 51% (125 ºC, 65 bar) to 74% (100 ºC, 90 bar); for C. crispus, values ranged between 26% (100 ºC, 90 bar) and 68% (140 ºC, 40 bar). Concerning C. crispus, gelling capacity in 0.1 M KCl was verified for all extracts except those obtained at 150 ºC, while for M. stellatus, gel was only formed with the extract obtained at 90 ºC and 65 bar. Thus, M. stellatus is more sensitive to high pressure and high temperature treatments than C. crispus. Gels from C. crispus are formed at higher temperature and are up to 30 times stronger than gels from M. stellatus, but are more brittle, in contrast to the strain hardening of M. stellatus gels. Overall, SWE gives hybrid carrageenan with better gel properties.