Physicochemical and pH-dependent functional properties of proteins isolated from eight traditional Chinese beans

Abstract

Mung bean (MPI), black bean (BPI), adzuki bean (API), rice bean (RPI), black kidney bean (BKPI), speckled kidney bean (SKPI), chickpea (CPI) and cowpea (CPPI) protein isolates were assessed for their surface (charge, hydrophobicity: H0 and tension) and functional properties (solubility, water/oil holding capacity, WHC/OHC; foaming capacity/stability, FC/FS; emulsifying activity/stability indices, EAI/ESI and least gelling capacity, LGC) at pH 3.0, 5.0, 7.0 and 9.0, using soybean (SPI) and pea (PPI) protein isolates as controls. Physicochemical properties of these proteins, e.g., amino acid composition and colour (L*, a* &b*, WI: whiteness index), were also characterized. API, RPI, BKPI, SKPI and CCPI exhibited a better amino acid profile and protein digestibility than other isolates. BKPI (27.01) and SKPI (20.48) showed higher WI, while CPI (−21.92) was the lowest. For all isolates, H0 was the highest at pH 3.0, followed by pH 7.0 and 9.0, while surface tension was the highest at pH 5.0, followed by pH 3.0. Compared to other proteins, BKPI and SKPI showed lower solubility, but were more effective to reduce surface tension. Most of the traditional legume proteins had similar EAI. CCPI showed better WHC/OHC and API, RPI, BKPI and SKPI displayed excellent FC/FS. Interestingly, LGCs of MPI (8%), BKPI (4%), SKPI (4%) and CCPI (6%) at pH 3.0 were significantly lower than other isolates (12%). Overall, BKPI and SKPI have good nutritional profiles and also possess excellent functionalities (except for WHC/OHC), which are very promising as new alternative legume proteins to SPI and PPI.