Aroma volatiles generated during extrusion cooking of maize flour

Volatile components in maize flour, extruded under different conditions obtained by varying product temperature (120, 150, or 180 °C), moisture level (14, 18, or 22%), and residence time (35 or 60 s), were identified and evaluated by gas chromatography/mass spectrometry (GC/MS) and GC olfactometry (GCO). Eighty compounds were identified in the headspace collections of the extrudates. Increasing the product temperature, reducing the moisture level, or prolonging the residence times generally increased the numbers and quantities of Maillard-derived compounds, such as pyrazines, pyrroles, furans, and sulfur-containing heterocycles. In low-temperature (120 °C) and high-moisture (22%) extrusions, the main volatiles were compounds associated with lipid degradation, with few compounds derived from the Maillard reaction. Increasing the temperature and reducing the moisture level to 18% gave rise to the formation of some pyrazines and thiophenones. A marked increase in quantities of 2-furfural, 2-furanmethanol, and alkylpyrazines occurred in the extrusions at 180 °C and 14% moisture level. Under these conditions, other nitrogen- and sulfur-containing heterocyclic compounds were also generated. GCO assessments identified 2-acetyl-1-pyrroline and 2-acetylthiazole as compounds that contributed to cereal-like odors of the extrudates. Some other sulfur-containing compounds were also believed to be involved in the aroma of extrudates processed at 180 °C and 14% moisture level.