Small and large deformation viscoelastic behaviour of selected fibre blends with gelling properties

Dietary fibres can be used as valuable functional ingredients in baked goods, as thickeners and gelling agents as a result of their ability to modify the structural properties of the matrix in which they are embedded. Viscoelastic behaviour of 12 selected gel–fibre blends (carboxymethylcellulose, hydroxypropylmethylcellulose, locust bean gum, high ester pectin, fructo-oligosaccharide and gluco-oligosaccharide) prepared at 10% concentration (w/v) was investigated at 25 °C and 95 °C by applying both fundamental and empirical rheological techniques to explore their usefulness/suitability as structural ingredients in diluted and weakened baking systems such as gluten free matrices. Mechanical and thermo-mechanical properties were recorded by using a controlled stress rheometer, measuring the storage modulus (G′), the loss modulus (G″) and the complex viscosity (η*). Textural characteristics were assessed by using a TAXTplus Texture Analyser with different attachments. Penetration and back extrusion tests were used for solid and liquid-like samples, respectively. The overall results indicated that (i) carboxymethylcellulose and pectin formed the strongest and the weakest gels, respectively, and that (ii) temperature had a significant effect on gel strength improvement especially for locust bean gum. A 30% substitution of hydrated fibres (cellulose derivates, galactomanans and high ester pectin) by prebiotics (fructo-oligosaccharides and gluco-oligosaccharides) led to a significant decrease of gel structure rigidity when compared to an identical system without prebiotic addition. Only locust bean gum exhibited an opposite behaviour inducing an increase in values of both dynamic moduli (G′ and G″) and static hardness. Significant relationships between dynamic (rheometry) and static (texture analysis) methods were found. Strengthening and structuring ability of some fibre blend gels endorsed them to be used as promising functional ingredients to make gluten-free bread by using low cost thickeners' agents.