Structure and performance of commercial kappa-2 carrageenan extracts: I. Structure analysis

Extracts of two Chilean carrageenophyte red seaweeds, Sarcothalia crispata and Gigartina skottsbergii, were prepared by each of two industrial processes: a mild alkaline extraction with aqueous sodium hydroxide and a more vigorous aqueous alkaline extraction with lime. The resulting extracts, recovered by precipitation with isopropyl alcohol, were separated into gelling and non-gelling fractions by leaching with 2.5% KCl. These processes were also applied to Chondrus crispus and to separated gametophyte and sporophyte samples of the Chilean seaweeds for comparative purposes. The carrageenan compositions of these extracts and fractions were determined using both chemical and spectroscopic techniques. In addition, a set of decision rules is proposed and applied to convert data from glycosyl linkage analysis to carrageenan composition. The gametophyte extracts contained mixtures/hybrids of kappa and iota carrageenans (and also mu and nu carrageenans, depending on the extraction conditions used). The tetrasporophyte extracts contained lambda carrageenan (and also theta carrageenan, depending on the extraction conditions used). Extractive fractionation of mixed life phase samples using 2.5% KCl yielded insoluble, ‘gelling’ carrageenans quite similar to those from a gametophyte extract of the same species, but the soluble, non-gelling fractions were not the same as the corresponding sporophyte extracts.