Quantitative Analyses of Key Odorants and Their Precursors Reveal Differences in the Aroma of Gluten-Free Rice Bread and Wheat Bread

Rice flour is one of the most important raw materials in gluten-free products. However, the aroma of gluten-free rice bread is less accepted by consumers than that of commercial wheat bread. Therefore, 18 selected aroma compounds were determined in rice and wheat breads by stable isotope dilution assays (SIDA) to elucidate differences in the sensory characteristics, concentrations, and odor activity values (OAVs). The OAVs of most aroma compounds varied greatly between a rice and a wheat bread. In particular, 2-aminoacetophenone with a grape-like, medicinal aroma was characteristic for rice bread crumb and crust, while maltol was only relevant in wheat bread crust. Ehrlich pathway products varied in their concentration between the bread crumbs and were correlated with the contents of their corresponding free amino acid precursors in the flours and doughs. The analysis of rice flour revealed that only a few aroma compounds were retained in the bread. Consequently, the bread making process has a high relevance in aroma compound formation. In a comparison of breads prepared from fresh and stored rice flour, hexanal was identified as an important indicator for aging in rice bread and flour.