Elsevier

Food Hydrocolloids

Volume 15, Issues 4–6, 11 July 2001, Pages 543-553
Food Hydrocolloids

Microstructure design in mixed biopolymer composites

https://doi.org/10.1016/S0268-005X(01)00062-5Get rights and content

Abstract

This paper is an overview of recent work on some particular aspects of the behaviour of biopolymer solution and gel mixtures, the focus being on aspects that are of particular relevance to the materials found in food systems. As such, the following areas are considered. (1) The phase behaviour of such mixtures in terms of the microstructures formed, the ideas of phase volume, phase continuity, surface tension and the use of the Flory–Huggins theory to model the behaviour. (2) The kinetics of phase separation in terms of the evidence for spinodal decomposition, ripening processes and the interplay between the kinetics of phase separation, gelation and molecular ordering. (3) The effects of shear on the composite microstructure in terms of particle size and shape, and how shear can be used to cause phase inversion of the system. (4) The material properties of the composites, including the fracture behaviour, the effect of particle size, and the role of the interface between the phases. It is clear that over the past few years a considerable literature has been built up on mixtures of biopolymers. Despite this growing understanding it remains a fact that we are not capable, as yet, of designing the microstructure of mixed biopolymer composites, although it is clear that there is a considerable technological advantage in being able to do so.

Introduction

Biopolymers and mixtures of biopolymers are used in many industries (e.g. Food, Pharmaceutical, Paint and Personal Care) to impart specific flow behaviours, textures, appearances and, where required, tactile and oral properties to products. As a consequence of this extensive use, many academic and industrial scientists have investigated their behaviour. Most of the studies however, have dealt with the equilibrium behaviour and the small deformation properties of the materials.

Thus far, there have only been limited studies in biopolymer mixtures of how the process of phase separation is related to the kinetics of molecular ordering and gelation (Alevisopoulos et al., 1996, Aymard et al., 2000, Clark et al., 1999, Loren and Hermansson, 2000, Loren et al., 2001, Owen and Jones, 1998). There have also been relatively few studies of the large deformation and failure response of materials formed in this manner, and of how this is influenced by the phase microstructure (Brownsey et al., 1987, Frith and Norton, 2000, Langley and Martin, 1994). Such microstructures may be, in turn, manipulated by the application of flow fields as the system is going through molecular ordering, gelation or phase separation events in order to produce materials with tailored properties (Wolf et al., 2001, Wolf et al., 2000).

All of these issues are of considerable importance to the production and properties of foods, hence, in this paper, we present an overview of recent and current work in the area. We also consider the subject of future studies that are required if we are truly to be capable of designing the microstructure and properties of mixed biopolymer composites.

Section snippets

Materials and methods

As this text is an overview of work in the area of mixed biopolymers, results are discussed that are based on studies of a variety of materials and experimental techniques. Detailed accounts of these are given in the publications referred to in the main text. In addition, a brief outline is given below of the materials and techniques discussed, along with the corresponding references.

Phase separation in biopolymer mixtures.

It has long been known that when biopolymers are mixed they often phase separate to form domains that are rich in one polymer and poor in the other (Beijerinck, 1910). Although this is entropically unfavourable, the enthalpy term is advantageous, as ultimately the molecules prefer to have neighbours of similar structure to ones that are dissimilar. This is, of course, particularly true when, as the temperature is lowered, the molecules start to interact and order, since interactions between

Conclusions

We have discussed some of the recent progress that has been made in the study of mixed biopolymer solutions and gels. Much of this work has focussed on the kinetics of the demixing process, the interface properties in such systems, and how these affect the bulk material properties of the mixtures. Notable advances include the following.

  • •

    Measurements can now be made of the interfacial tension in phase separated systems. The value obtained is three orders of magnitude below those observed for

Acknowledgements

The authors would like to thank T. Foster, P. Knight, S. Pomfret, K. Plucknett, B. Wolf, M. Williams, L. Lundin, V. Normand, M. Butler, M. Heppenstall-Butler and A. Clark for many helpful discussions and for kindly allowing their data to be reproduced here.

References (43)

  • J. Ryden et al.

    Interfacial tension of dextran-polyethylene glycol-water two-phase systems

    Journal of Colloid & Interface Science

    (1971)
  • B. Wolf et al.

    Shear-induced anisotropic microstructure in phase-separated biopolymer mixtures

    Food Hydrocolloids

    (2000)
  • S.H. Zhu et al.

    Transition of phase continuity induced by crosslinking and interfacial reaction during reactive processing of compatibilized PVC/SBR blends

    Polymer

    (1998)
  • E. Amici et al.

    Interpenetrating network formation in gellan-agarose gel composites

    Biomacromolecules

    (2000)
  • Y.A. Antonov et al.

    Liquid two-phase water-protein-polysaccharide systems and their processing into textured protein products

    Journal of Texture Studies

    (1980)
  • P. Aymard et al.

    A turbidimetric study of phase separating biopolymer mixtures during thermal ramping

    Langmuir

    (2000)
  • M.W. Beijerinck

    The formation of an emulsion by mixing solutions of some gel forming colloids

    Kolloid Zeitschrift

    (1910)
  • G.J. Brownsey et al.

    Elasticity and failure in composite gels

    Journal of Rheology

    (1987)
  • Butler M., & Heppenstall-Butler M. (2001). Phase separation in gelatin/maltodextrin/gum arabic mixtures studied using...
  • A.H. Clark

    Kinetics of demixing

  • A.H. Clark et al.

    Interpenetrating network formation in gellan-maltodextrin gel composites

    Macromolecules

    (1999)
  • Cited by (0)

    View full text