Quantitative Analysis of Aroma Compounds in Wheat and Rye Bread Crusts Using a Stable Isotope Dilution Assay

A stable isotope dilution assay was developed for the quantitative analysis of acetylpyrazine, 2-methyl-3-ethylpyrazine, 5-methyl-5/f-cyclopenta[6]pyrazine, and 2-acetyl-l-pyrroline in bread crusts. Model experiments showed that these compounds, which contribute significantly to the crust flavor, can be determined with high sensitivity and accuracy. The method revealed that the levels of the three pyrazines lie in similar concentration ranges in the wheat and rye crusts. In contrast, 2-acetyl-l-pyrroline appeared at an approximately 20-fold higher concentration in wheat crust than in rye. Comparison of two different processes for rye bread revealed that the level of the four compounds was twice as high in the three-stage sourdough than in the one-stage process.