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A new fractionation method for kappa- and lambda-carrageenans isolated from Gigartina pistillata (Rhodophyta)

Gigartina pistillata (GMELIN) STACKHOUSE harvested commercially along the Atlantic coast of Morocco is generally a mixture of gametophytes with a cell wall enriched in κ-carrageenan, and tetrasporophytes with a wall composed mainly of λ-carrageenan. In order to separate both polysaccharides, two extraction methods were investigated. The first one involved sequential extraction in water with increasing temperatures in 20 °C increments starting from 20 °C up to 100 °C. The second method was carried out by using successive ethanol concentrations (100, 80, 60, 40, 20 % and water). Chemical characterization of the different fractions revealed that low extraction temperatures or high ethanol concentrations contained mainly the κ-carrageenan. In contrast, high extraction temperatures or low ethanol concentrations yielded λ-carrageenan enriched fractions. These results demonstrate that the use of these distinct methods can selectively extract κ- or λ-carrageenans to improve the quality of the final carrageenan product and increase the value of raw algal material in Morocco.