AROMA VOLATILES GENERATED DURING EXTRUSION-COOKING OF MAIZE FLOUR

Volatile components in maize flour, extruded under different condition s obtained by varying product temperature (120, 150, or 180 degrees C) , moisture level (14, 18, or 22%), and residence time (35 or 60 s), we re identified and evaluated by gas chromatography/mass spectrometry (G C/MS) and GC olfactometry (GCO). Eighty compounds were identified in t he headspace collections of the extrudates. Increasing the product tem perature, reducing the moisture level, or prolonging the residence tim es generally increased the numbers and quantities of Maillard-derived compounds, such as pyrazines, pyrroles, furans, and sulfur-containing heterocycles. In low-temperature (120 degrees C) and high-moisture (22 %) extrusions, the main volatiles were compounds associated with lipid degradation, with few compounds derived from the Maillard reaction. I ncreasing the temperature and reducing the moisture level to 18% gave rise to the formation of some pyrazines and thiophenones. A marked inc rease in quantities of 2-furfural, 2-furanmethanol, and alkylpyrazines occurred in the extrusions at 180 degrees C and 14% moisture level. U nder these conditions, other nitrogen-and sulfur-containing heterocycl ic compounds were also generated. GCO assessments identified 2-acetyl- 1-pyrroline and 2-acetylthiazole as compounds that contributed to cere al-like odors of the extrudates. Some other sulfur-containing compound s were also believed to be involved in the aroma of extrudates process ed at 180 degrees C and 14% moisture level.