Small deformation rheological properties of maltodextrin-milk protein systems

Small deformation dynamic oscillation was used to investigate the structural behaviour of conformationally dissimilar maltodextrin and milk protein macro-molecules in a mixture, with the view of identifying the state of phase separation and the pattern of solvent distribution between the two constituent phases. The enthalpic nature of the maltodextrin network produced a sigmoidal transition in the development of storage modulus (G') during cooling and substantial thermal hysteresis upon heating of the gel. By contrast, the entropically-driven build up of structure in milk protein samples yielded linear and overlapping cooling and heating scans of G' with networks reverting into solutions at relatively low temperatures. These differences in the viscoelastic functions of the two polymers in combination with theoretical analysis (isostress-isostrain models, Kerner equation) have documented the reinforcing effect of strong and spherical maltodextrin inclusions on the weaker and continuous milk protein phase. However, at concentrations of maltodextrin beyond the phase inversion point, the binary assembly comprises a strong and continuous maltodextrin network surrounding the weaker milk protein inclusions. Finally, the sharp change in the pattern of water partition between the two polymeric components, as a result of phase inversion in the system, was rationalised on the basis of kinetically-influenced co-gels comprising phase separated networks which are trapped away from the state of thermodynamic equilibrium. Copyright (C) 1996 Published by Elsevier Science Ltd