Characterisation of kappa- and iota-carrageenan coils and helices by MALLS/GPC

Abstract

Iota- and kappa-carrageenans were degraded by ultrasonication to obtain samples of different molecular weights. The coil and the helix conformations of the degraded and non-degraded samples were investigated by multi-angle laser light scattering (MALLS) coupled to gel permeation chromatography (GPC), and the weight-average molecular weight, M w , as well as the z-average radii of gyration, R g , z , was obtained for all samples in both conformations. The conformational state was controlled by temperature and/or electrolyte content. All measurements were done under non-aggregating conditions, and an approximate doubling of the weight-average molecular weight was seen for both iota- and kappa-carrageenan helices over the entire molecular weight range studied, implying a double-helix formation. Zimm plots for non-degraded kappa-carrageenan coils and helices confirmed the approximate doubling of the molecular weight for the helix conformation.