THERMAL EXTRUSION AND ALKALI PROCESSING OF DRY BEANS (PHASEOLUS-VULGARIS L)

Dry beans are an important source of protein but contain antinutritional factors. An important antinutrient is phytohemagglutinin (PHA), a heat-labile lectin known to depress the nutritional quality of dry beans. This work was undertaken to evaluate the utility of two processes that may aid in the inactivation of PHA, extrusion and cooking in a high pH medium. Extrusion was found to be relatively ineffective in reducing the activity of PHA of whole red kidney or black beans. Extrusion was more effective but highly variable in reducing the PHA activity of bean flours (25-80%). However, soaking and cooking beans at high pH was very effective, significantly reducing the activity of PHA and also reducing the time required to reach a palatable texture. Soaking and cooking dry beans at high pH also caused significant changes in the saline soluble protein extract as determined by gel electrophoresis. High pH cooking treatment may be useful in improving nutritional quality of dry beans.