Abstract
The Chilean granado bean (Phaseolus vulgaris L.) contains nutritionally
valuable proteins, and there was indication that the proteins can help
in the prevention of diabetes. To further explore tis potential purified
samples of the bean proteins is required. A membrane-based process was
developed for the isolation of proteins from granado beans, adapted from
methods reported earlier for mustard protein processing. The optimised
process consists of alkaline protein extraction from granado bean flour
at pH 10, ultrafiltration at concentration factor 4 and diafiltration
with diavolume 4 followed by isoelectric protein precipitation at pH 4.
The process starting with granado beans containing 28% protein,
recovered 60.1% of the protein as precipitated protein isolate (PPI)
and 7.2% as acid soluble protein isolates (SPI). The losses in the
process system were approximately 26% of mass and 18.8% of nitrogen
due to removal of non-protein nitrogen and small molecular weight
components, likely carbohydrates. The protein contents of the PPI and
SPI were ~92 % and ~ 62% on a
moisture-free basis; the protein content of the SPI produced is
considerably lower than typical isolates. This may be due to the
co-recovery of high molecular weight carbohydrates. The water absorption
capacity and nitrogen solubility index, of the PPI and SPI were measured
and compared to other oilseed isolates. The PPI showed high water
absorption (<400%). SPI dissolved completely – a nitrogen
solubility index of 100%, while PPI had low nitrogen solubility near
its isoelectric point. Both isolates had traits desirable for easy
incorporation into food products.