LIGNIFICATION: EVIDENCE FOR A ROLE IN HARD-TO-COOK BEANS

Abstract

An investigation was undertaken to establish whether lignification was a possible mechanism contributing to the hard-to-cook defect in beans (Phaseolus vulgaris). Cell wall material (CWM) from control and defective beans was isolated and microscopic techniques employed to compare the two fractions. Transmission electron microscopy indicated that potassium permanganate-fixed material had heavier deposition of manganese dioxide in cell corners, secondary walls and middle lamella of hard beans, a pattern seen during the lignification of plant tissue. CWM from hard beans had a lamellated appearance not seen in the control as viewed by scanning electron microscopy. It is suggested that this is a result of cellulose deposition, a process known to occur before lignification. This tentative evidence of lignin within the cell walls of legume seeds has a host of implications for hydration during cooking, cell separation and ultimately, texture.