Compositional and rheological analysis of carrageenan from the gametophyte phase of the red seaweed Chondrus crispus neutrally extracted at varying temperatures and time

Abstract

Carrageenan-rich precipitate (CRP) was extracted from gametophyte Chondrus crispus at varying temperatures (22 °C, 45 °C, 90 °C) and time (0.25 h, 2 h, 8 h) at neutral conditions (i.e. without addition of alkali). Lower levels of 3,6-anhydrogalactose were detected in CRPs extracted at room temperature (22 °C) compared to extractions at 45 °C and 90 °C, suggesting a lower proportion of gelling units. Meanwhile, the CRPs obtained during the first period of extraction (0.25 h, at 45 °C and 90 °C) showed a higher amount of sulphate as compared to extractions for 2 or 8 h, suggesting a higher proportion of precursor units. These compositional differences were also supported by rheological studies. Gels made from CRP extracted at 22 °C had lower shear elastic modulus (G’) compared to gels made from CRP extracted at higher temperatures (45 °C, 90 °C). This was likely due to the lower 3,6-anhydrogalactose content in the extraction made at room temperature. In addition, the viscosity of gels made from CRP extracted at 0.25 h were higher compared to gels made from CRP extracted at 2–8 h for the same temperature (45 °C or 90 °C). This could be due to the higher amount of sulphate detected in the CRP of the former. Since 3,6-anhydrogalactse is an indicator of transformed (gelling) units, this result suggested that carrageenan chains with higher proportion of precursor units are more extractable under mild conditions. This knowledge may lead to the possibility for selective carrageenan extraction. • There are various carrageenan fractions in the seaweed cell walls that differ in terms of extractability in water. • Carrageenan fraction extracted at 22 °C contains lower amounts of 3,6-anhydrogalactose. • Gels made from carrageenan fraction extracted at 22 °C exhibits lower G’ values. • Carrageenan fraction obtained during the first period of extraction (0.25 h, at 45 and 90 °C) contains higher proportion of sulphate units. • Gels made from carrageenan obtained during the first period of extraction (0.25 h, 45 and 90 °C) exhibits lower viscosity values.