Extraction and Characterization of Cereal Protein Fractions

Defatted flours (2 × 50 g) were extracted three times each with 200 mL of (a) salt solution by homogenizing with an Ultra Turrax blender (16 000 rpm, IKA-Werke, Staufen, Germany) in a centrifuge vessel for 5 min at 22°C. The suspensions were centrifuged (3750 × g, 25 min, 22°C) and the supernatants discarded (→ ALGL fraction). The sediments were extracted three times with 200 mL of (b) ethanol/water as described for the ALGL fraction. The resulting supernatants were combined, concentrated under reduced pressure, dialyzed (M_r cut-off: 12 000–14 000, Medicell Membranes, London, UK) and lyophilized (→ prolamin fraction). Then, the sediments were extracted three times under nitrogen with 200 mL of (c) glutelin solution (see above) by homogenizing with an Ultra Turrax blender for 5 min, stirring for 30 min at 60°C, cooling and centrifugation as described. The supernatants were combined, concentrated, dialyzed and lyophilized (→ glutelin fraction). For oat flour, the extraction was stopped after the prolamin fraction (M_r cut-off for dialysis: 7 000, Medicell Membranes), because oat glutelins are mainly composed of polymeric 12S globulins [30 ]. The CP contents of the dried prolamin and glutelin fractions were determined according to ICC Standard 167 (n = 3) [24 ].