Structural and functional characterization of freeze-dried fibrillated pinto bean protein isolate

Protein concentrations and protein isolates can be made from legume seeds. Pinto bean protein isolate was heated at 85 °C and pH 2 for 5, 10 and 20 hours before forming fibrillar aggregates. Three different techniques- Congo red spectrum analysis, Fourier Transform Infrared spectroscopy (FT-IR) and Transmission Electron Microscopy (TEM)- were used to find these nanofibrils after being freeze-dried. Congo red spectrum was right-shifted from about 500 nm in standard congo red solution to about 534-536 nm in fibrillated pinto bean protein isolate. FT-IR spectra peak, moved from 1630 cm -1 in native pinto bean protein to 1619 and 1618, in protein solutions fibrillated for 10 and 20 hours, respectively. However, TEM scans revealed that the aggregates after 20 hours of heating were numerous than aggregates from 10 hours of heating. After fibrillation, the average percentage of three replicates for protein degree of hydrolysis (DH) of pinto bean protein isolates heated for 5, 10, 20 hours, was increased initially and then decreased due to fibrillation. Electrophoregrams of freeze-dried fibrillated proteins showed hydrolysis of the main band of native protein. Functional properties including Emulsion Activity Index and Emulsion Stability Index, lowered upon fibrillation treatment; while Water Holding Capacity and Oil Holding Capacity increased.