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-degrees-C for 10 min whereas unsoaked beans required 20 min of heat treatment at 97.8-degrees-C. Residual lectin activity was eliminated by thermally processing the presoaked and unsoaked beans for 25 and 50 min at 97.8-degrees-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-degrees-C.