Rates of structure development during gelation and softening of high-methoxyl pectin—sodium alginate—fructose mixtures

Structure development (SD) rates, defined as: (dη*/dt) (Pa.s/s), were determined during gelation and melting of high-methoxyl (HM) pectin—Na alginate—fructose mixtures containing 55% and 65% fructose, 0.75% total polymer with ratios of HM pectin—Na alginate: 1/3, 1/2, and 2/3. In comparison with HM pectin—fructose gels (i.e. without Na alginate), the addition of Na alginate resulted in substantial increase in SD rates, and there were maxima in the SD rates over the range 25–35°C depending on the amount of sugar and the ratio of HM pectin to Na alginate. During heating of the gels containing Na alginate, melting (—SD) rates were high at lower temperatures and reached near zero values at higher temperatures. The effect of temperature in the vicinity of the maximum SD rates during gelation and melting could be described by the Arrhenius relationship. With the exception of the data with highest pectin concentration, magnitudes of the activation energy (Ea) of gelation curves were higher than those of the melting curves.