Changes in the concentrations of potent crust odourants during storage of white bread

The headspace volatiles of the crust from both freshly baked and stored (96 h) white bread were evaluated by aroma extract dilution analyses (AEDA). In the fresh crust, 3‐methylbutanal (malty), 2‐acetyl‐1‐pyrroline (roast) and butane‐2,3‐dione (buttery) appeared with the highest FD‐factors, followed by 2‐methylpropanal, oct‐1‐en‐3‐one, 2‐ethyl‐3,5‐dimethylpyrazine and (E)‐non‐2‐enal with lower FD‐factors. During storage a stale off‐odour was formed in the crust. This was reflected by the AEDA: the FD‐factors of 3‐methylbutanal, 2‐acetyl‐1‐pyrroline, butane‐2,3‐dione, pentane‐2,3‐dione and methional were significantly lowered in the crust of the stored white bread, while the FD‐factors of oct‐1‐en‐3‐one, 2‐ethyl‐3,5‐dimethylpyrazine and (E)‐non‐2‐enal remained unchanged. Quantitative measurements of five odourants by stable isotope dilution assays established that the stale off‐odour formed during storage of white bread was caused by the rapid loss of key odourants of the fresh bread, e.g. 2‐acetyl‐1‐pyrroline and 3‐methylbutanal, and the retention of those formed by lipid peroxidation, e.g. (E)‐non‐2‐enal.