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-r otating machine. The final barrel zone and die temperatures were 150+/ -3 degrees C and 150+/-7 degrees C, respectively. The residence time w as 32 s, the moisture content of the feed was 18% (m m(-1)) and the fe ed pH was 4.0, 5.0 or 7.7. Isolates of the volatile components were pr epared using continuous steam distillation-solvent extraction with pen tane:ether (9:1, v/v) as the solvent. Analysis by gas chromatography-m ass spectrometry resulted in the identification of 32, 20 and 16 compo unds, respectively, from each isolate. At pH 7.7, nitrogen compounds d ominated 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 wa s 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 mor e than 60% greater at pH 7.7 than at the other pH values. Copyright (C ) 1996 Elsevier Science Ltd.