STRUCTURE-PROPERTY RELATIONSHIPS IN FOOD BIOPOLYMER GELS AND SOLUTIONS

This paper serves as a review of work performed in the author's and hi s collaborators' laboratories over the last 15 years on the general to pic of structure/property relationships for biopolymer (including food biopolymer) solutions and gels. In the first part, we describe how sm all deformation oscillatory measurements have enabled a distinction to be made between ''entanglement networks,'' ''strong'' and ''weak'' ge ls used, respectively, as food thickeners, gels, and stabilizers. At s mall enough strains both strong and weak gel systems give essentially the same mechanical spectrum, with G' > G '', and with both moduli lar gely independent of frequency. However, the deformation dependence of these two classes of materials is very different. At large deformation s strong gels will rupture and fail, while weak gels flow without frac ture and but show recovery of solid (gel-like) character. In this pape r the various classes of food biopolymers are described, and their the ological properties related to differences in structure. The final par t contrasts the behavior of a weak gel (xanthan gum) and entanglement solution (guar gum). This distinction is confirmed by their respective responses in start shear experiments. Guar solutions behave much like most other polymer solutions, whereas xanthan solutions show a very p ronounced overshoot peak at low strains, and very long peak overshoot recovery times. (C) 1995 Society of Rheology.