Structure–property relationships in food biopolymer gels and solutions

This paper serves as a review of work performed in the author’s and his collaborators’ laboratories over the last 15 years on the general topic of structure/property relationships for biopolymer (including food biopolymer) solutions and gels. In the first part, we describe how small deformation oscillatory measurements have enabled a distinction to be made between ‘‘entanglement networks,’’ ‘‘strong’’ and ‘‘weak’’ gels used, respectively, as food thickeners, gels, and stabilizers. At small enough strains both strong and weak gel systems give essentially the same mechanical spectrum, with G′≳G″, and with both moduli largely independent of frequency. However, the deformation dependence of these two classes of materials is very different. At large deformations strong gels will rupture and fail, while weak gels flow without fracture and but show recovery of solid (gel-like) character. In this paper the various classes of food biopolymers are described, and their rheological properties related to differences in structure. The final part 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 pronounced overshoot peak at low strains, and very long peak overshoot recovery times.