Physicochemical Characterization of Carrageenans-A Critical Reinvestigation

摘要

Kappa-, iota-, and lambda-carrageenan (food grade) were analyzed by static light scattering (MALS in batch mode) in DAM NaNO3 at 25 and 60 degrees C, earlier heated up to 90 degrees C or not. At 25 degrees C, there was a strong tendency for a concentration-dependent aggregation in the order lambda < kappa < iota. At 60 degrees C, all samples were molecularly dispersed. The strongly temperature-dependent refractive index increments (equilibrium dialysis) differ. Data interpretation in terms of the wormlike chain model using the Skolnik-Odijk-Fixman approach led to an intrinsic persistence length around 3 to 4 nm and expansion factors as high as 1.5 and above in a thermodynamically good solvent for all three types. Triple-detector HPSEC (DRI, MALS, viscometry) on the three commercial samples plus a degraded (by acidic hydrolysis) kappa-carrageenan in the same solvent/eluant at 60 degrees C yielded a uniform and slightly Curved [eta]-M relationship for 5 x 10(3) <= M/(g mol) <= 3 x 10(6) and a nearly identical molar mass dependence of the radius of gyration. HPSEC at 25 degrees C on kappa-carrageenan confirmed formation of soluble aggregates. Special emphasis was Put on analytical and methodological aspects. The reliability of the experimental data was demonstrated by analogous measurements on dextran calibration standards. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3508-3524, 2008