Structure and performance of commercial κ-2 carrageenan extracts. Part Ⅲ. Structure analysis and performance in two dairy applications of extracts from the New Zealand red seaweed, Gigartina atropurpurea

摘要

Extracts of a New Zealand carrageenophyte red seaweed, Gigartina atropurpurea, were prepared under conditions simulating those used in 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 extraction processes were also applied to separated gametophyte and sporophyte samples of the same seaweed. The carrageenan compositions of these extracts and fractions were determined using modern chemical and spectroscopic techniques. The gametophyte extracts contained mixtures/hybrids of κ and ι carrageenans (and also μ and ν carrageenans, depending on the extraction conditions used). The tetrasporophyte extracts contained a complex λ-type carrageenan (including θ carrageenan, depending on the extraction conditions used). Fractionation of extracts from mixed life phase samples using 2.5% KCl yielded gelling carrageenans quite similar to those from a gametophyte extract of the same species, but the non-gelling fractions were not the same as the corresponding sporophyte extracts. The performance of the extracts and fractions was evaluated in two commercial dairy applications: cold- and hot-processed chocolate milks. The structures of the carrageenans in the various extracts from G. atropurpurea and their performance in cold- and hot-processed chocolate milks were compared with those equivalent extracts analysed previously from Chondrus crispus, Sarcothalia crispata and Gigartina skottsbergii.