A new method is presented to determine the phase diagram of mixed aqueous biopolymer systems using Fourier transform infrared spectroscopy coupled with partial least-squares analysis. We present the equilibrium phase diagrams of aqueous amylopectin/gelatin mixtures allowed to phase separate at a temperature outside the range within which either polymer could gel. The method is capable of detecting the changes in the phase diagram when the molecular weight of one of the components is altered. The phase diagrams are analyzed in terms of the Flory-Huggins theory for ternary systems. The method we have developed can be extended to any other combination of polymers in solution which show sufficient spectral difference.

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Weak amylopectin gels have been formed directly following dissolution of waxy maize granules. Rheological characterisation of these gels has been carried out as a function of stress and frequency. The gels are visually clear and homogeneous, and environmental scanning electron microscopy shows no trace of the original granules remaining. It is postulated that the origin of the gel network lies in pairwise aggregation of outer chains of the amylopectin molecules, presumably via double helix formation. However, these pairs of chain segments do not aggregate to develop crystallinity.

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We present results which show how Fourier transform infrared (FTIR) microspectroscopy can be used as a valuable tool in the study of phase-separated mixed biopolymer solutions and gels. The work in this paper deals specifically with the ternary amylopectin-gelatin-DjO system which forms thermoreversible gels when a hot mixed solution is cooled to room temperature. First, we show how the integrated area of particular infrared absorption peaks from the two polymers can be used as an estimate for composition, and we use this approach to monitor the spatial fluctuations in composition by tracking across a sample and also to monitor changes in composition with time at fixed position. We also use this approach to establish the scale upon which phase separation takes place by taking the infrared spectrum over a range of sampling sizes at fixed position. Second, we use FTIR microspectroscopy coupled with partial least-squares analysis to determine quantitatively polymer concentration in the micro-phase-separated domains of a mixed gel. From a comparison of these concentrations with the previously determined equilibrium phase diagram of this system, we find that for samples held for long enough above the gelation temperature of either component before quenching, the concentration in the phase-separated domains of the gel are the same as those found at equilibrium in the liquid-liquid bulk phase-separated phases.

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