Foaming and emulsifying properties of pea albumin fractions and partial characterisation of surface-active components

Whole albumin of pea seed (Palb) was extracted from pea flour (var Frilene) by solubilisation at pH 4.9 and dialysis against water. Palb was fractionated by differential solubilisation in 60% methanol, yielding a soluble (S60) and an insoluble (IS60) fraction. The composition of the fractions was determined by SDS-PAGE and RP-HPLC. Albumins exhibited a wide variability of surface hydrophobicity. Albumin PA2 was present as a major component in Palb and IS60. Low-MW hydrophobic albumins were concentrated in S60. Foaming and emulsifying properties of the three extracts were determined in model conditions. Functionality of albumins was highest at acid pH, but the fractions differed in their properties. The presence of PA2 albumin resulted in the best foaming and emulsifying properties. This protein was shown to adsorb preferentially at air/water and oil/water interfaces, whereas low-MW hydrophilic albumins did not. Low-MW hydrophobic albumins were also adsorbed at interfaces, as shown by the behaviour of the S60 fraction, but they formed more fragile films than did PA2. This was related to the structure of the polypeptide chains.