Thermal stability of black turtle soup bean (Phaseolus vulgaris) lectins

A method for determining the thermal stability of porcine thyroglobulin (PTG)‐binding lectins in whole black turtle soup beans ( Phaseolus vulgaris L) is described. The procedure utilises PTG‐Sepharose affinity chromatography and the Folin‐Ciocalteau protein assay. The majority of lectin activity in whole black turtle soup beans was destroyed by heating presoaked beans at 97.8°C for 10 min whereas unsoaked beans required 20 min of heat treatment at 97.8°C. Residual lectin activity was eliminated by thermally processing the presoaked and unsoaked beans for 25 and 50 min at 97.8°C, respectively. Thermal inactivation of the lectin in the whole seed is a biphasic, first‐order reaction mechanism. Lectin‐rat intestinal epithelial cell binding studies indicated the presence of a second lectin in the BTS albumin protein fraction. The lectin lacked an affinity for PTG and was inactivated by heating unsoaked whole beans for 50 min at 97.8°C.