Confocal Raman microscopy of frozen bread dough

• We investigated frozen wheat bread dough by confocal Raman microscopy.
• The phase distribution within the frozen dough was assessed.
• Starch, gluten, ice, liquid water and yeast distribution were imaged.
• Ice could be identified very reliably based on its specific Raman spectrum.
• Ice appeared as a continuous phase within the frozen dough.

The use of freezing technology is well established in industrial and craft bakeries and is still gaining importance. In order to optimize recipes and processes of frozen baked goods, it is essential to be able to investigate the products' microstructure. Especially ice crystals and their interaction with the other components of the frozen products are of interest. In this study, frozen wheat bread dough was investigated by confocal Raman microscopy. The Raman spectra measured within the dough were compared with spectra of the main components of frozen dough, i.e. ice, liquid water, starch, gluten and yeast. In this way, the spatial distribution of the single components within the dough was determined and corresponding images of the frozen dough microstructure were generated. On these images, ice appears as a continuous network rather than as isolated crystals. We suggest that this method may be appropriate for characterizing crystallization phenomena in frozen baked goods, allowing to better understand the reasons for quality losses and to develop strategies for avoiding such losses.