Relaxation spectrum of doughs: influence of content and type of biopolymers

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

Buenos Aires

Jornada; VI Jornadas Internacionales de Proteínas y Coloides Alimentarios; 2011

Facultad de Ciencias Exactas y Naturales de la Universidad de Buenos Aires

Gluten contains the protein fractions glutenin and gliadin; their interactions through covalent and non-covalent bonds to form gluten complexes result in viscoelastic dough that exhibits cohesive, elastic and viscous properties. In recent years, gluten-free bakery products have an increase demand because of the improvement in celiac disease (CD) diagnosis. Hydrocolloids and proteins are essential ingredients in gluten-free doughs for improving their rheological properties and final appearance. Rheological studies become particularly useful when predictive relationships for rheological properties of foods can be developed based on the molecular architecture of the constituent species. This work compares linear viscoelastic characteristics of gluten-free and commercial doughs formulated with wheat flour. The effect of proteins (dry egg and ovoalbumin), hydrocolloids (xanthan and locust bean gums), and water contents on the rheological behavior of gluten-free doughs was also studied. Small amplitude oscillatory data (storage G?, and loss moduli, G??) were used to obtain the mechanical relaxation spectra (H()) of the systems. The broadened Baumgaertel-Schausberger-Winter (BSW) equation was successfully used to model H(). Gluten-free dough exhibited similar elastic modulus to those prepared with wheat flour. However commercial wheat flour dough presented higher loss tangent values. The gluten matrix is more easily deformed under applied stress, and it is possible to correlate this behavior with large deformation experiments in which dough formulations are submitted to extensibility tests. In gluten-free doughs starch granules probably act as inactive fillers because of their inability to form a cohesive network, which is mainly formed by the xanthan and locust bean gums. Dough with 35.5 % water presented the highest values of elastic modulus, exhibiting a more pronounced plateau. The parameters of the BSW model could be used to explain structural characteristics of the systems. The slope of the spectrum in the entanglement regime, together with the spacing between characteristic times, decreased when more water was added to the formulation. The higher value of the slope in the plateau region may be related to the development of a more entangled network. A significantly higher value of the plateau modulus was also observed in the formulation with the lowest water content. This tendency was in agreement with the behavior of the other parameters. The increase in gums content produced an increase in both moduli (G? and G??) and a more elastic dough was obtained. G? was always larger than G?? in the frequency measured range and the increase of the two moduli with frequency was small. There was a marked change when gum content increase from 0.5% to 1.5%. Both the plateau modulus and the width between characteristic times showed a positive correlation with the hydrocolloids increment reflecting a decrease in the molecular mobility. 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 notice the difference in the characteristic relaxation parameters of these systems.