Gelling characteristics and rheology of kappa/iota-hybrid carrageenans extracted from Mastocarpus stellatus dried at different temperatures

Abstract

The effect of the seaweed drying temperatures (35, 45, 55 and 85 °C), prior to the biopolymer extraction, on the rheological properties of kappa/iota-hybrid carrageenan (KI) gels in NaCl extracted from Mastocarpus stellatus seaweed is reported, together with the thermal stability of obtained gels. The average molecular mass (ranged between 2.25 × 106 and 1.02 × 106 kg kmol−1) of extracted KI, determined by gel permeation chromatography, and estimated intrinsic viscosities (ranged between 0.935 and 0.258 m3 kg−1), conducted in a capillary viscometer, decreased with increase of the seaweed drying temperatures. The parameters (K and a) of the Mark-Houwink-Sakurada (MHS) equation for KI are also reported. Thermo-rheological oscillatory measurements were conducted in a stress-controlled rheometer in order to clarify the kinetics of gel formation and to characterize the structure of the matured gels. Rheological results indicated a weakening of the KI gelling properties at smaller average molecular masses (i.e. larger seaweed drying temperatures, above 45 °C). Even so, KI samples exhibited stable and weak gel properties (i.e. elastic modulus <200 Pa). KI gels reached stability after 20 min of maturation. Cooling and heating profiles showed a strong temperature dependency. Gel setting temperatures significantly depended on the biopolymer content, whereas gel melting temperatures (68.0 ± 0.3 °C) were unvaried. No complete thermal stability was observed for gels formed with tested biopolymers, the most thermal stable being those prepared with KI with larger molecular masses (i.e. lower seaweed drying temperatures, below 45 °C).