Molecular Interactions Between Xanthan Gum, Psyllium, Milk Proteins and Starches, and Their Implications on Gluten-Free Bakery Products

Sammanfattning: Gluten in bread can cause severe health problems in patients with celiac disease. However, gluten-free substitutions often show impaired quality characteristic like a liquid dough because of a missing gluten-network or accelerated staling due to the high amount of gluten-free starch. Therefore, hydrocolloids are considered to improve gluten-free bread quality characteristics. The idea of this degree project was to understand the interactions between xanthan gum and specific bread ingredients on a molecular basis with subsequent analysis of xanthan gum’s function in gluten-free dough and bread. The molecular interactions between xanthan gum, psyllium, starches and milk powder were tested as model systems in water-salt solutions and analysed by rheological measurements, i.e. amplitude sweep, temperature sweep and apparent viscosity profile. Based on these analyses, two types of gluten-free doughs and breads were prepared, one of which contained 1.2% xanthan gum and the other not. The doughs were analysed using rheometry, moisture analysis, texture analysis and kneading behaviour. Moisture analysis as well as texture analysis was performed after baking bread loafs of both types of dough. The analysis of molecular interactions showed that the addition of xanthan gum increased the overall rigidity and viscosity when mixed with starches and psyllium. Also, the combination of xanthan gum with starches resulted in a lower pasting temperature compared to starches without xanthan gum probably due to enhanced starch granule swelling. In contrast to that, the behaviour of the xanthan gum and milk powder formulation seemed to be xanthan-gum driven. The derived effects on gluten-free dough and bread based on the molecular interactions in solution could be partially confirmed in the analysis of dough and bread. For example, the incorporation of xanthan gum to gluten-free dough resulted in a more rigid dough with less moisture release during moisture analysis compared to the gluten-free dough without xanthan gum. The different properties of both tested gluten-free breads showed the thickening effect of xanthan gum, which led to lower baking loss and higher loaf weight with a firmer bread texture in comparison. Also, the observed lower moisture content in the crust of the bread with xanthan gum could probably delay retrogradation and bread staling. From these results it can be concluded that xanthan gum can act as a moisturizer and thickener for gluten-free bread and affects the molecular behaviour of gluten-free starches and psyllium.