RESUMO
Wheat flour was extruded using a single- and double-screw extruder at 130, 150, and 170 °C, respectively, to determine the effect of extrusion on the content and possible modifications of protein in wheat flour. Regarding to proteins, their yield under non-reducing extraction conditions (in SDS only) decreased to one-third after extrusion-but remained constant after extraction under reduced conditions (in SDS + DTT). This phenomenon possibly reflected protein cross-linking through intermolecular disulfide bonds to gluten proteins, especially at high temperature and high screw speed during double-screw extrusion, as suggested by the increased number of free-SH-groups and reduced intensity of low-MW proteins in SDS-PAGE under this extrusion condition. Lysinoalanine was not detected in the extruded gluten fraction, indicating that non-disulfide bonds did not develop under the extrusion conditions. Furthermore, the reducing sugar content also decreased to > 50% only in all double-screw samples, indication Maillard reaction may contribute to protein modification during extrusion to some extent. Eventually, protein modification during extrusion may affect the celiac gluten toxicity of wheat gluten assessed by total gluten content and potential celiac toxicity.