THE EFFECT OF TECHNOLOGICAL QUALITY AND EXTRUSION PROCESSING IN GLUTEN PROTEIN PROFILE OF WHEAT FLOURS

Wheat is considered the most suitable raw material for pasta and baking products due to its unique viscoelastic properties. The study aimed to access the changes in the protein profile of wheat flours (Triticum aestivum) presenting contrasting technological end-use qualities after thermoplastic and cold extrusion processes. Two wheat genotypes (ORS Agile; ORS Vintecinco) were used firstly to obtain flour, then the extrudates, applying two different screw rotation speeds (150 and 300 rpm), and pasta by cold-extrusion process with further cooking. Protein extracts were sequentially extracted based on the Osborne fractions – salt-soluble (AG), ethanol-soluble (Gli), SDS-soluble with reduction (Glu). All extracts were characterized by RP-HPLC, AG were calculated by total area and Gli and Glu subunits by using PWG-gliadin (Prolamin Working Group) as calibrant. Total protein content ranged from 8.6% to 13.8%, this variation can be due to the diversity of processes even considering the same genotype. Extruded samples shown the same behavior in the protein profile for both genotypes, with a decrease in AG and Gli and increase of Glu content, indicating the protein insolubilization. The highest gluten polymerization occurred with the increasing of the screw rotation speed. The protein profile of raw and cooked pasta was also similar for both genotypes. AG and Gli contents were decreased when sample was submitted to the cooking process, with the increasing of Glu. These changes might be explained by the high temperature applied during the pasta cooking process promoting modifications in the gluten polymer due to the participation of monomeric subunits (soluble) that before cooking were extracted in the AG and Gli fractions and after cooking are part of the Glu polymers. The Gli/Glu ratios were significantly lower than the respective wheat flours for all samples, except for raw pasta, which follows the same Osborne distribution as wheat flour. Gli and Glu subunits were separated and ω-5-, ω-1,2-, α-, γ-, ωb-gliadins, HMW and LMW-GS contents were assessed. ω-5- and ω-1,2-gliadin were the less affected by wheat flour processing in both genotypes. α- and γ-gliadins, as well as LMW-GS, were mainly responsible by promoting interactions contributing to improve the gluten fraction. Remarkably and contrary to ORS Agile, pasta samples from ORS Vintecinco showed much higher α-gliadin amounts than γ-gliadin. The γ-gliadin content in 300 rpm extrudate was the lowest when compared to other ORS Agile samples. Considering the crude protein content determined by Kjeldahl, ORS Agile was strongly impacted by processing, since the protein recovery in these samples (~59%) was considerably lower than in ORS Vintecinco (~94%). Independent of the type of processing applied, wheat genotypes showed different protein recovery yield. The bread/improver wheat (ORS Agile) produces a stronger gluten network than ORS Vintecinco, classified as biscuit wheat. The highest gluten force rendered more difficult the protein extract in the ORS Agile samples after processing. Thermoplastic extrusion decreased protein extractability more than cold extrusion, but cooking pasta intensified the protein cross-linkages. Further analysis, as the application of proteomic approaches, can be used to characterize the differences in protein expression in the samples.