Effect of decortication, germination and extrusion on physicochemical and in vitro protein and starch digestion characteristics of black beans (Phaseolus vulgaris L.)

Black beans (BB) are a rich source of carbohydrates and proteins, and an excellent source of antioxidants with potential pharmacological use. Decortication (D) and extrusion (Ext.) processes have been applied to different seed sources to diversify their use, while germination (G) have shown to improve bioavailability and potential health benefits of both starch and protein fractions. The focus of this work was to investigate the effects of decortication and germination of black beans and their combinations with thermoplastic extrusion on some functional and physicochemical characteristics as well as their effects on in vitro protein and starch digestion rates. The combination of germinated beans plus decortication and extrusion (BBGD + Ext. 145) resulted in higher water and oil absorption capacities (3.5 and 3.9 g/g, respectively), along with reduced trypsin inhibitor activity (from 0.4 to 0.1 TIU/mg). Overall, germination promoted a decrease on the starch content, whilst extrusion produced further depolymerization of amylose molecules. The comparative predicted glycemic indexes (pGI) of the black bean flour and the extruded counterpart (BBGD + Ext. 145) were 60 and 85%, respectively. ATR-FTIR analyses indicated molecular interactions between proteins and depolymerized starch molecules, which yielded moderate pGI, as well as the functional properties and improvements in protein digestibilities.