Linear viscoelasticity of non-fermented dough: effect of gluten absence

V. LARROSA; G. LORENZO; N. ZARITZKY; A. CALIFANO

Viscoelasticity: Theories, Types and Models

NOVA Publishers

Lugar: New York; Año: 2011; p. 93 - 113

Gluten is a proteinaceous material that can be separated from wheat flour when the starch and other minor components of the flour are removed by washing out under running water. The resulting tough, viscoelastic, and sticky material contains about one third of protein and two thirds of water. It is the structure-forming complex in wheat, responsible for the viscoelastic properties needed to produce good quality baked products. Gluten contains the protein fractions glutenin and gliadin. The former is a rough, rubbery mass when fully hydrated, while gliadin produces a viscous, fluid mass on hydration. Therefore, interactions of gliadins and glutenins through covalent and non-covalent bonds to form gluten complexes result in viscoelastic dough that exhibits cohesive, elastic and viscous properties that combine the extremes of the two components. It has the ability to withstand stresses applied during mixing and to retain gas during fermentation and baking, enclosing the starch granules and fiber fragments. In recent years, gluten-free bakery products have an increase demand because of the improvement in coeliac disease (CD) diagnosis. CD is a pathology affecting the upper small intestine mucosa due to an inappropriate immune response to gluten protein fractions, which are mainly present in wheat, barley, and rye. The only effective treatment for coeliac disease is strict adherence to a gluten-free diet throughout the patient´s lifetime, which, in time, results in clinical and mucosal recovery.The absence of gluten often results in liquid batter rather than a dough or products with a crumbling texture, poor color and other quality defects may be obtained. Thus, the addition of substances that mimic the viscoelastic properties of gluten are always required in order to provide structure. Hydrocolloids and proteins are essential ingredients in gluten-free doughs for improving their rheological properties and final appearance. The selection of a hydrocolloid for a processed food often depends on the unique properties of the starch or gum, as suitability is related to underlying physicochemical properties imparted by the component, their interaction with water and other food ingredients.The rheological characterization of doughs provides important information for food technologists, allowing ingredient selection strategies to design, improve, and optimize the final product. Rheological studies become particularly useful when predictive relationships for rheological properties of foods can be developed which start from the molecular architecture of the constituent species. This chapter focuses on the linear viscoelastic characterization of gluten-free non-fermented doughs and the effect of proteins (dry egg and ovoalbumin) and hydrocolloids (xanthan and guar gums) content. Small amplitude oscillatory data (storage modulus, G´, and loss modulus, G´´) was used to obtain the relaxation spectrum and compare it to the spectrum of a traditional wheat dough.The increase in gums content produced an increase in both moduli (G´ and G´´) and a more elastic dough was obtained. G? was always greater than G´´ in the frequency range measured and the increase of the two moduli with frequency was small. The broadened Baumgaertel-Schausberger-Winter model was successfully used to predict the mechanical relaxation spectrum from dynamic oscillatory data.Gluten free doughs exhibited similar elastic modulus to those prepared with wheat flour. However, analyzing the tan(d) vs. frequency curves, commercial wheat flour doughs presented distinctively higher values, which correspond to a more viscous contribution. The gluten matrix is more easily deformed under applied stress, and it is possible to correlate this behavior with large deformation experiments when doughs are submitted to extensibility tests.Using the mechanical spectrum all dynamic data could be converted into the time domain by the application of BSW model. From the relaxation curves thus obtained, it could be noticed the difference in the characteristic relaxation parameters of these systems.