Hybrid carrageenans from Betaphycus gelatinus: Physicochemical and rheological properties

A hybrid sulfated galactan (x-/(3-carrageenan) was extracted from wild and cultivated Betaphycus gelatinus using cold (25 degrees C) and hot (95 ... 110 degrees C) alkaline extractions, followed by alkali treatment to convert residual precursors into primary carrageenan forms. Structural analysis of native and alkali-treated galactans from both sources using HP-SEC, HPICE, HPAEC, FTIR, FT-Raman, and NMR revealed no significant differences in molecular weight, monosaccharide composition, sulfate content, or structural characteristics. NMR analyses confirmed that alkali treatment converted y-carrageenan into (3-carrageenan through desulfation. Enzymatic depolymerization with x-carrageenase further investigated the distribution of x- and (3-carrabiose moieties. It was confirmed that the enzyme-resistant fraction was enriched in (3-carrageenans, whereas the enzyme-sensitive fraction contained abundant oligo x- or x/(3-carrageenans, indicating a block-wise distribution of x- and (3-carrageenan diads in the polymer. Dynamic rheometry was used to assess the effects of alkali treatment and counter ions (K+, Ca2+, Ba2+) on the thermo-rheological properties of the hybrid galactan gel. This study provides the first evidence of the strong gel-forming capability of Betaphycus polysaccharides, especially in cultivated samples with K+ ions. It also highlights the impact of block-wise versus random distribution of x- and (3-moieties on gel formation. Alkali-modified x/(3-carrageenans from B. gelatinus emerge as a sustainable, versatile hydrocolloid with promising applications in the food industry, due to their excellent solubility, controlled gelation, and ability to form transparent, thermo-reversible gels under low salt conditions.