The effect of pH on the volatiles formed in an extruded starch-glucose-lysine model system

Starch-glucose-lysine extrudates were produced using a twin-screw co-rotating machine. The final barrel zone and die temperatures were 150 ± 3 °C and 150 ± 7 °C, respectively. The residence time was 32 s, the moisture content of the feed was 18% (m m−1) and the feed pH was 4.0, 5.0 or 7.7. Isolates of the volatile components were prepared using continuous steam distillation-solvent extraction with pentane:ether (9:1, v/v) as the solvent. Analysis by gas chromatography-mass spectrometry resulted in the identification of 32, 20 and 16 compounds, respectively, from each isolate. At pH 7.7, nitrogen compounds dominated the isolate and pyrazines accounted for over 80% (m m−1) of the volatiles. At pH values of 5.0 and 4.0, the yield of pyrazines was less than 10% of that at pH 7.7 and furans comprised more than 80% (m m−1) of these aroma isolates. The yield of total volatiles was more than 60% greater at pH 7.7 than at the other pH values.