Chemical and microstructural evaluation of 'hard-to-cook' phenomenon in legumes (pinto bean and small-type lentil)

Some physicochemical and microstructural characteristics of hard-to-cook (HTC) and easy-to-cook (ETC) pinto beans and small-type lentils were compared. The development of HTC seeds was monitored over 6 months for changes in physicochemical properties. Results indicated that hardness, extent of water absorption and solid loss of HTC legumes were, respectively, 21-97%, 7-72% and 62-236% higher than those of ETC legumes. In addition, darkening of HTC beans and lentils was significantly higher than those of ETC ones. Scanning electron microscope observations indicated deteriorations in cytoplasmic contents of cotyledon cells of hard seeds. Phytic acid and total phenolic contents were, respectively, decreased 36-61% and 43-61% during storage, whereas hardness of seeds was increased 3-6 times. The soaking of hard seeds in sodium solutions resulted in the improvement in legume texture.