Designing biopolymer fluid gels: A microstructural approach

I Fernández Farrés,R.J.A Moakes,I.T Norton

doi:10.1016/j.foodhyd.2014.03.014

Abstract

Fluid gels are suspensions of gelled particles whose elasticity and physical dimensions can be manipulated to impart a range of material properties. The formation and physical properties of fluid gels are discussed with the focus being on the process–structure relationship.Recent work in this area has led to the development of new techniques for the production of thermo-stable fluid gels. An overview is provided on these techniques which have been successfully employed to produce thermo-stable fluid gels from both alginate and proteins.An enhanced understanding of the molecular events occurring during fluid gel formation is outlined which has enabled greater control over the microstructure. This has allowed the production of small (<10 μm), spherical and reasonably soft particles which resemble oil droplets. These particles when used in emulsion based products to replace a significant proportion of the oil, show rheology matching that of the full fat original product.Increasing the volume fraction and elasticity of fluid gel particles has been shown to decrease the friction measured at the contact between the soft surfaces of a tribometer. This ability of fluid gel particles to provide lubrication through entrainment to the contact zone suggests that fluid gels have the potential to impart sensory attributes typically associated with fat.Directions for future research are also discussed which may provide further insights into food structuring and breakdown thereby assisting the design of more complex structures with novel functional attributes.

Highlights

Biopolymers have traditionally been used in the food industry to provide structural stability and to impart desirable texture to a wide range of products including emulsions
We have discussed the formation of fluid gels from polysaccharides undergoing thermal gelation where the conformational ordering kinetics are controlled by the rate of cooling which can be matched to the time scale of the applied shear rate (Fig. 4A)
Current findings indicate that the stiffness and inter-particle interactions of alginate particle produced via in-situ calcium release can be controlled to give a range of viscoelastic responses

Summary

Introduction

Biopolymers have traditionally been used in the food industry to provide structural stability and to impart desirable texture to a wide range of products including emulsions. The production of fluid gels was restricted to polysaccharides, polysaccharides which undergo thermo-reversible ordering transitions, but recent developments have enabled the production of thermally stable fluid gels This have allowed for a much wider range of applications in the food industry. Tribological results from oil-in-water emulsions were shown to correlate well with sensory data, providing an insight into the processes occurring in the oral cavity during food consumption. This correlation relates to the fact that the structure of the emulsion deforms into a thin film during the last step of food processing in the mouth, as a result of the movement of the tongue against the palate before swallowing. The disordering transition that occurs during the first heating cycle (melting the fluid gel) can be assessed by comparison with that of its corresponding quiescent

Thermo-reversible fluid gels from polysaccharides

Alginate fluid gels

Protein fluid gels

Fluid gel lubrication