Hybrid beta/kappa/gamma-carrageenan from the red alga Betaphycus gelatinus in Vietnam

Abstract

The red alga Betaphycus gelatinus showed little monthly variation in carrageenan yields, 3,6-anhydrogalactose and sulfate contents for the native carrageenans (68.2 – 73.1%, 23.1—24.8% and 17.9 – 20.3%, respectively) and for alkali-modified carrageenans (23.7 – 31.5%, 41.6 – 43.9% and 8.6 – 8.8%, respectively). The gelling and melting temperatures and 1.5% gel strength of alkali-modified carrageenans from April to June showed no change, with the recorded values of 40.8 °C, 74.5 °C and 310 g cm⁻², respectively. The molecular weight of the native carrageenan was evaluated as 876 kDa by GPC. ¹H and ¹³C NMR spectra proved that the carrageenan is composed predominantly of a hybrid of beta-carrageenan and kappa-carrageenan. The relative peak areas of the α-anomeric proton signals in ¹H NMR spectra and the signal intensities of the anomeric carbons in ¹³C NMR spectra indicated that the native carrageenan showed little variation in the relative proportions of beta-carrageenan and kappa-carrageenan (52:48), but after alkali-modified carrageenan, the beta-carrageenan component increased significantly compared to the kappa-carrageenan component (69:31). These results will contribute more information on hybrid carrageenan from the red alga B. gelatinus in Vietnam.