5.1.2. Effect of ageing on the aroma quality
The principal reasons for the deterioration of the aroma quality of baked goods are because of the loss of some of the most important odorant compounds during ageing and the formation of ‘‘off-flavours’’ originated from lipid oxidation. These two events are the reasons for the dramatic decrease in the flavour quality of baked cereal products that will make the product unacceptable for consumption. Soon after baking, a process of gradual but unstoppable deterioration in quality begins. This process of changes is referred as ‘‘staling’’ and manifests itself principally by a loss of flavour and an increase in crumb firmness (Van Dam & Hille, 1992). After baking, some of the most important odorant compounds such as pyrazines disappear very rapidly via evaporation of the volatile compounds of the crust. After 3 h at room temperature there is a loss of 47% and after 24 h the loss is of 74% of acetyl-pyrazine (Grosch & Shieberle, 1997). The other important process that takes place during ageing of baked cereal goods is the generation of volatile compounds from lipid oxidation, such as hexanal and (E)-2-nonenal. The elaboration method may also have an influence on the concentration of stale aldehydes. Zehentbauer and Grosch (1997) have shown that 1 and 4 h after baking the Strecker aldehydes (methylpropanal, 2 and 3-methylbutanal) that also disappeared via evaporation decreased about 45 and 50% for the baguettes produced by the industrial method and about 24% and 27% in the baguettes produced by the traditional method. The formation of the stale aldehydes and the loss of compounds with pleasant roasty notes such as pyrazines increase the stale off-flavour perceivable after storage of wheat bread (Schieberle & Grosch, 1992).