Antinutritional, functional, thermal, rheological properties, and in vitro digestibility of soaked and germinated black bean (Phaseolus vulgaris L.) flours

This study investigated the effect of soaking and germination treatment on the physicochemical, antinutritional, functional, rheological, thermal properties, and in vitro digestibility of black bean flours (BBFs). The results indicated that the protein content of BBFs significantly (p < 0.05) increased during the soaking and germination process, showing the greatest incline, i.e., from 26.67 to 28.04%. The trypsin inhibitor activity, tannin content, and phytic acid content of BBFs reduced significantly (p < 0.05) from 6.59 to 10.25 TIU mg^− 1, 1.45–3.78 mg CE g^− 1, and 5.83–9.45 mg g^− 1, respectively, after soaking and germination, which may have resulted in an increase in the in vitro protein digestibility. Regarding techno-functional properties, there was a significant increase of 30.09–40.87% and 24.34–49.56% in water absorption capacity and oil holding capacity, respectively. Similarly, the emulsion stability of raw BBFs, initially at 68.23%, showed a significant increase with extended soaking (24 h) and germination (72 h), rising to 78.56% and 80.01%, respectively. SEM images and FT-IR spectra revealed alteration in morphology and amorphous regions of soaked and germinated BBFs. In addition, treated BBFs formed gels with final viscosities which were 33–38% higher than that of the raw sample. Thus, it can be concluded that soaking (24 h) and germination (72 h) have been proven to be an effective approach to producing legume flours possessing diverse nutritional properties in BBFs, which can be employed in the formulation of various functional food items.