Curdlan gels form either by neutralization of alkaline solutions or by heating aqueous suspensions. The former gels consist of long rnicrofibrils, 20 to 25 nm wide, made up of subunits, 2-3 nm wide. The microfibrils disintegrate on sonication into fibril units which on heating loosen and release thinner elementary fibrils, 1-3 mm wide.
Heated gels are composed of electron-dense structures in pseudocrystalline form. Preparations having their average degree of polymerization (DPn) 200, are unable to form gels.
Agar, K- and t-carrageenans, and konjac glucomannan gels formed by cooling of heated sols have structures similar to gels produced by neutralization of their alkaline solutions. Both neutralized and heat-induced gels are composed of long microfibrils, about 5-25 run wide. Viscous solutions of A-carrageenan, scleroglucan, succinoglycan, xanthan gum, pullulan, and dextran are composed of shorter rnicrofibrils, 1-2 nm wide. Sodium salts of K-carrageenan, alginate, gellan gum, and low-methoxyl pectin form gels in the presence of potassium or calcium ions. The microfibrils in these gels are considerably longer and/or wider than in the sols. Locust bean gum does not gel alone but yields gels containing fibrous or globular forms when mixed in solution with xanthan gum or K-carrageenan and potassium ions. Fibrous structures of amylose and amylopectin in starch gels appear to be similar. Short-chain amylose (D!'n 57 and 78) consists of branched microfibrils about 10 mm wide.
Molecular association resulting in the formation of long and/or wide rnicrofibrils in rod-like or globular forms is supposedly one of the prerequisites for polysaccharides to form gels.
Harada, Tokuya; Kanzawa, Yoshimi; Kanenaga, Kazuko; Koreeda, Atuo; and Harada, Akira
"Electron Microscopic Studies on the Ultrastructure of Curdlan and Other Polysaccharides in Gels Used in Foods,"
1, Article 1.
Available at: http://digitalcommons.usu.edu/foodmicrostructure/vol10/iss1/1