Microscopic imaging of network strands in agar, carrageenan, locust bean gum and kappa carrageenan/locust bean gum gels

Abstract

The ultrastructure of gels formed from agar, kappa carrageenan, iota carrageenan, locust bean gum and mixtures of kappa carrageenan and locust bean gum have been studied by fast-freeze deep-etch rotary-shadowed replica microscopy. The reproducibility of images obtained suggests that the technique is robust and preserves features of native network architecture at the nanometre level. Agar gels show a range of strand thicknesses, whereas kappa carrageenan has a more homogeneous structure. Iota carrageenan network strands are thinner than those in kappa carrageenan, but thicker than those in locust bean gum gels. Mixed gels of kappa carrageenan and locust bean gum indicate thorough mixing and, therefore, no phase separation at the 10–100 nm level. Apparent binary polymer contacts are consistent with, but do not prove unequivocally, the presence of inter-polymer associations.