Effect of thermal processing methods on flavonoid and isoflavone content of decorticated and whole pulses

Legumes have always been consumed as a staple source of proteins, and they are the only dietary source of isoflavones, flavonoid class of secondary plant metabolites. Isoflavones impart physiological effects via estrogenic action in humans and hence, looked upon as potential replacement of hormone estrogen in its deficiency. Legumes are an integral part of the Indian staple diet. Legumes are processed by soaking, germination, and thermal cooking. These methods have been reported to modify the nutrient composition of legumes. The sample population was surveyed to determine the most commonly used household processing methods. Soaking or germination followed by pressure cooking (with or without direct contact of water) or open pan cooking was found to be commonly followed by cooking practice in Indian households. Amongst the decorticated pulses, the highest cooking time was taken by chickpea (Cicer arietinum), and lentil (Lens culinaris) was cooked in the least amount of time. The pressure-cooked decorticated chickpea showed a 63% decrease in TFC and isoflavone content while open pan cooking lowered TFC of chickpea up to 67% and isoflavone content up to 90%. TFC of pressure-cooked and open-pan cooked decorticated lentil was only reduced by 12-17%, while isoflavone content showed 60-80% depletion. TFC of whole legumes was reduced by 30-40% on pressure cooking as well as open pan cooking; however, isoflavone content was variably affected. The black-eyed pea and desi chickpea showed 40% reduced isoflavone content while the loss of isoflavone content was 70% for kidney bean. Germination of green gram significantly increased the TFC and isoflavones, which showed a decrease of 24% and 44%, respectively, on pressure cooking.