Rheological Characterization of Low‐methoxyl Pectin Gel by Normal Creep and Relaxation

Abstract

Fourteen low-methoxyl pectins were used to prepare a 30% sucrose gel with a final pectin concentration of 0.8% and an added calcium content of 25 mg Ca"/gpectin. The texture of each gel was evaluated using three descriptors: firmness, coarseness, and graininess. The relaxation behavior of the 14 gels, under a constant strain, was monitored using an Instron universal testing machine. The data were best defined by an equation that is represented by two Maxwell bodies in parallel. The elastic moduli and relaxation times o f this model ranged, between gels, f r o m 2881 Pa to 5487 Pa and from 4.1 s to 908 s, respectively. A n apparatus constructed in this laboratory was used t o measure the creep behavior of the gels under constant stress. The normal creep behavior o f the 14 gels was best defined by the Burger's Model. The elastic moduli and viscous constants of this model ranged, between gels, from 3937 Pa to 15,342 Pa and from 20,300 P1 to 40,100 P1, respectively. The relaxation modulus, E , , was the most sensitive f o r distinguishing significant differences between the gels. Several significant correlations were found between rheological, ch e m ica 1 and t e x t u ral param e ters. '

Rheological and Structural Properties of High‐methoxyl Esterified, Low‐methoxyl Esterified and Low‐methoxyl Amidated Pectin Gels

“…Our primary objective was to determine how small and large deformations affect the structural and rheological properties of HM, LM, and LMA pectin gels at room (20C) and refrigeration (5C) temperatures. This extends the work of others (Gross et al . 1980; Rao and Cooley 1994).…”

Rheology of polysaccharide systems

“…Whatever the number of Maxwell elements, the resulting behavior is typical of a viscoelastic liquid. In several cases, a satisfactory fitting can be obtained with the four-parameter equation resulting from the combination of only two Maxwell units in parallel [479][480][481]. In terms of relaxation Young's modulus, we have:…”

Direct Stress‐strain Dynamic Characterisitcs of Low‐methoxyl Pectin Gels

“…The results of sensory and chemical analysis and their relationship to one another has already been discussed in detail in a related publication (Gross et al 1980). The means of [El, 0, El and E2, calculated from the 6 observations for the 14 LM pectin gels, accompanied by a n analysis of variance and the Duncan's New Multiple Range Test, are listed in Table l and 2.…”

“…For the different types of rheological tests performed on the gels (other tests detailed in Gross et al 1980 andGross 1979), dynamic variables were most highly correlated to texture, and seemed to be the most useful tool in understanding gel structure. Not only is dynamic testing a quick method, but it allows one to carefully select a test frequency which may be best suited for obtaining the desired information for the material being tested.…”