H. J. Cooley

The isolation and characterization of a water extract of konjac flour gum

Abstract An aqueous extract from konjac flour was dried, milled and redispersed in water, prior to its characterization by viscometry and rheometry. The rate of change of relative viscosity with reciprocal absolute temperature was of a magnitude less than that of some other polar polysaccharides by a factor approximating 2. The volume-concentration relationship was non-linear in water, but linear in 0·04 m tartaric acid. The hydrophilicity of this extract in 0·04 m tartaric acid was only 0·68 g g −1 solute/100 g dispersion, much less than that of many of the commonly used polysaccharides. The intrinsic viscosity was 1320 ml g −1 , among the highest of the polysaccharides. Considering the relatively low water affinity, the high viscosity of the konjac extract was attributed mostly to solute-solute interaction, rather than to hydration, at functional use-levels. The dried, redispersed extract was characterized in both steady and dynamic shear by the Carreau and Cross equations, and by the Cox-Merz rule. Deviation from the Cox-Merz rule was attributed to molecular associations of time scales longer than non-specific physical entanglements.

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

Abstract 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 ( E a ) of gelation curves were higher than those of the melting curves.

Rheological Changes During Sol-Gel Transition of Pectin-Sucrose/Fructose Dispersions

Frequency sweeps over 20–40°C revealed weak-gel behavior of the pectin gels. At 20°C, during sol-gel transition, both G′ and G″ increased with time, rapidly in the initial stages and slowly later. Pectin gels made with sucrose showed higher G′ than those made with fructose. Structure development rates during 24 h were higher initially.