Physicochemical changes in Pisum sativum L. and Phaseolus vulgaris L. proteins induced by extrusion cooking

There were no differences in the nitrogen content of pea and kidney bean se ed before and after extrusion (P=0.104 and P=0.256, respectively). The amou nt of protein extracted after thermal treatment was reduced both in water a nd in the NaCl solutions in the pH 1-13 range. The protein solubility of ex truded pea and kidney bean flour decreased significantly (P < 0.05) compare d with raw seed: 71 % and 82 % in Tris-Gly-EDTA (pH 8.0) buffer. However, t he relative solubility was nearly 100 % in buffer with SDS plus urea and 2- mercaptoethanol (ME), in both raw and extruded samples. Total and free sulp hydryl groups and disulphide content decreased after extrusion-cooking in p ea proteins (35 %, 74 % and 6 %, respectively P < 0.05) and in kidney bean proteins (60 %, 61 % and 4 %, respectively P < 0.05). The water-holding cap acity (WHC) of extrudates increased significantly in both peas and kidney b eans (57 % P < 0.05 and 32 % P < 0.05, respectively). A reduction (25 %, P < 0.05) in oil absorption capacity (OAC) was observed in extruded kidney be an flour.