κ-carrageenan and β-lactoglobulin interactions visualized by atomic force microscopy

Mixes of kappa-carrageenan and beta-lactoglobulin were observed by atomic force microscopy (AFM). Diluted kappa-carrageenan solutions showed helix formation and strand heights between 1 and 3 nm. Upon mixing beta-lactoglobulin with carrageenan, AFM still revealed the presence of native protein with heights between 2 and 6 nm and the protein seemed to affect side-by-side aggregation of carrageenan. After heating, a network of beta-lactoglobulin aggregates formed and the unheated protein was not affected by the presence of kappa-carrageenan. At all the concentrations used in the study we observed phase separation. When studying the mixed gels under solid contact conditions, the surface topography of the samples clearly indicated phase separation and lack of interaction between beta-lactoglobulin and kappa-carrageenan. In general, the present research demonstrated how AFM imaging allowed direct visualization of mixed biopolymer systems such as beta-lactoglobulin and kappa-carrageenan. These observations were discussed in light of mechanisms of interactions previously suggested using other analytical techniques. (C) 2003 Elsevier Ltd. All rights reserved.