Antioxidant and angiotensin-I converting enzyme inhibitory activities of phenolic extracts and fractions derived from three phenolic-rich legume varieties

Lentil, black soybean and black turtle bean are commonly consumed legumes of different genera, containing high phenolic contents, which are effective antioxidants and angiotensin-I converting enzyme (ACE) inhibitors. However, these legumes' phenolic compositions and ACE inhibition ability have not been compared. Crude water extract (CE) was semi-purified (SPE) and fractionated using column chromatography. Results showed that purification and fractionation could substantially increase phenolic contents and antioxidant capacities. Heating and variety had great effect on phenolic substances, antioxidant potential and mass yield of extracts and fractions. Only crude extracts showed potent ACE inhibitory activity. Black turtle bean's ACE inhibition potential was largely reduced by cooking. The order from low to high in terms of ACE inhibitory activity was black turtle bean < lentil < black soybean. Identification and quantification of individual phenolic compounds by UV spectroscopy and LC-MSn analysis confirmed 18, 22, and 14 compounds, respectively, for the three legumes.