Effect of extrusion cooking on structure and functional properties of pea and kidney bean proteins

Pea (Pisum sativum L cv Ballet) and kidney bean (Phaseolus vulgaris L cv Pi nto) seeds were extruded at 148 and 156 degrees C respectively. Protein sol ubility at various pH values and in various solvents was determined and ana lysis of protein fractions was carried out by SDS-PAGE. Also, sulphhydryl a nd disulphide groups, water-holding capacity (WHC), water solubility index (WSI) and oil absorption capacity (OAC) were determined. No changes in tota l nitrogen content of pea and kidney bean seeds occurred as a result of the rmal treatment. Protein solubility from raw and extruded legumes was signif icantly higher in saline solutions than in water in the pH range 2-10. The solubility of proteins from extruded pea and kidney bean flours was greatly decreased with respect to native flours when extraction was in buffer (pH 7.0) alone. Extraction with buffer containing 2-mercaptoethanol (2-ME) or s odium dodecyl sulphate (SDS), alone or in combination, greatly increased pr otein extractability. As a result, the relative solubility was nearly 100% in buffer with SDS and 2-ME for both raw and extruded samples. Total and fr ee sulphhydryl group and disulphide contents decreased significantly (P <0. 05) after extrusion cooking. Moreover, extrusion treatment caused major cha nges in the band patterns of the albumin and globulin fractions obtained by SDS-PAGE. WHC and WSI of extrudates increased significantly in both peas a nd kidney beans. A significant reduction in OAC was observed in extruded ki dney bean flour. (C) 2000 Society of Chemical Industry.