Temperature dependence of the formation and melting of pectin-Ca2+ networks:: a rheological study

Small deformation dynamic rheometry was used to characterise the calcium-induced gelation of low-methoxyl pectins, at two different pH values. The gelation kinetics was interpreted with basis on the change of the storage modulus with time, taken as a measure of changes in cross-linking density within the pectin-calcium network. The temperature influence on the rate of gel formation and ageing was evaluated, as well as the temperature sensitivity of the cured gels. The formation and the softening/melting of pectin-calcium networks were also studied under non-isothermal conditions. The structural diversity of the two pectin samples had a great influence on the gelation kinetics and thermal behaviour of these pectin-calcium networks, due to differences in the steric arrangement or environment and/or availability of the chelating groups.. An association mechanism is suggested to predominate under conditions of low availability of dissociated carboxylic groups, due to a low pH, higher degree of methylation, or steric constraints introduced by acetylation or neutral side chains, different from the classical 'egg-box' model, and where non-ionic hydrogen bonding and hydrophobic interactions may co-exist and cooperate with coordinative binding of calcium-ions. (C) 2003 Elsevier Ltd. All rights reserved.