ALBUMINS FROM THE BEAN PHASEOLUS VULGARIS: EFFECTS OF HEAT TREATMENT

Bean albumins heated at different temperature and time intervals (60C to 135C, 1 to 30 min) suffered a reduction of in vitro digestibility, proportional to the intensity of treatment. The electrophoretic (SDS-PAGE) and chromatographic (gel filtration) profiles showed the formation of high molecular weight protein aggregates, involving disulfide bonds. More intense heat treatments caused formation of bonds not broken by β-mercaptoethanol or SDS, resulting in aggregates resistant toproteolysis. Determination of available lysine showed that these residues were not implied in possible crosslinking reactions, and heated albumins showed the same amino acid profile as the control. The decrease of SH groups upon heating followed a first order kinetics, with an activation energy of 76.9kJ/mol, and an increasing k value ranging from 0.0012 at 60C to 0.267 at 135C. DSC thermograms of albumins showed two peaks, with maximum denaturation temperature of 87C and 98C, and total enthalpy of denaturation of 7.7 J/g.