The influence of sucrose and sorbitol on gel–sol transition of low-methoxyl pectin+Ca2+ gels

Melting temperatures (Tm) of low-methoxyl (LM) pectin+Ca2+ gels were strongly dependent on LM pectin concentration, and on the presence of sucrose and sorbitol. Enthalpy (ΔHm) (kJ mol−1) of melting of the gels was determined from Eldridge–Ferry plots; ΔHm of sucrose gels was higher than those of plain gels (43.1 kJ mol−1) while that of sorbitol gels was lower, reflecting the important role of the hydroxyl groups in sucrose and sorbitol. Structure loss rates (SLR), defined as (−dG′/dt) (Pa s−1), were determined during melting of LM pectin+sugars gels. The SLR versus temperature profiles were bell-shaped curves with maximum values over the ranges (24–35°C) depending on the amount of pectin and sugars. Based on a reference LM pectin concentration, a reduced SLR (SLRR) versus reduced temperature (TR) master curve could be constructed for LM pectin gels with different pectin concentrations and at a fixed sugar content. The effect of temperature on SLR was described by the Arrhenius relationship, and the estimated activation energy (Ea) was between 7.26 and 350 kJ mol−1.