A microwave spectroscopy study for gluten-free bread doughs

Gluten-free products market is experiencing a noticeable growth, due to the worldwide increase of celiac disease and intolerances. Among gluten-free products, bread is the most challenging food to replace, since gluten-free flours have a complex microstructure and processing. Microwave (MW) dielectric spectroscopy can help to provide insights in food composition and structure. However, the dielectric spectra of gluten-free doughs have never been investigated. In this study, we systematically investigate the dielectric properties of gluten-free doughs. We analyzed the dielectric response of raw ingredients using an open-ended coaxial probeinthefrequencyrangef ∈ [0.2,4]GHzandthenevaluated the feasibility of using mixing formulas to predict the gluten-free dough spectra. Homogenization formulas are not able to predict the MW dielectric response of gluten-free doughs. Therefore, we tested the multipole Debye, Cole-Cole, and the Havriliak–Negami dielectric models. The three-pole Cole-Cole model is the best di electric model, resulting in an average relative percentage error of 0.84% and 0.65% on the real and imaginary parts, respectively. After identifying the best dielectric model, we have used it to fit the spectra of 54 doughs with variable water, yeast, and salt content, thus providing, for the first time, an MW spectroscopy framework to define the dielectric properties of this food material. From our investigations, it turned out that salt increases the dielectric losses, yeast affects the energy storage, but water plays the main role in determining doughs properties. Comparing the dielectric spectra of gluten and gluten-free doughs, we observed relevant differences for dry, wet, yeast-free, and salt-free cases, but a similar dielectric spectrum was found for the reference dough composition.