Sucrose Pectin Interaction from Solution to Gels

Pectin is a very important polysaccharide in food technology, due to its ability to thicken or gel in aqueous solution under specific condition. One of the most common uses of pectin is in making jellies or jams, which requires the addition of a large amount of sucrose to acidic solutions. The role of sucrose in promoting pectin gelation has been ascribed to the strengthening of hydrophobic interaction consistently with its well-known stabilizing effect on protein structure. On the other hand, more specific effects on dimension and stiffness of pectin chains have been suggested by computational work. Here we present measurements of rheology, static and dynamic light scattering on samples of pectin containing different amounts of sucrose, ranging from few percent up to close the solubility limit of sucrose. This corresponds to spanning from low viscous liquid samples to strong gels. Results show that below the threshold value of 55% w/w, sucrose acts a critical parameter for the sol/gel transition by increasing the strength of excluded volume and hydrodynamic interaction between polymer chains. A further increase of sucrose above the critical concentration yields gels with a higher viscoelastic component corresponding to a higher amount of frozen structural inhomogeneities.