Pea flour was extruded under various conditions; extrusion treatment was characterised by specific mechanical energy (SME), moisture content, shear rate at the die and product temperature. Product transformation was measured by starch solubility, protein solubility in specific buffers and by immunoassay with anti-legumin antibodies. Response surfaces showed that SME influenced starch and protein solubility more than did temperature. Decrease of protein solubility was attributed to formation of non-covalent bonds and disulphide bonds which could partly take place at the die, according to flow conditions. The most severe extrusion conditions (SME>250 kWh t−1) led to the creation of other covalent bonds. Immunoassay proved an efficient method for assessing the severity of treatment by following the loss of legumin antigenicity.