Separation of minor protein components from whey protein isolates by heparin affinity chromatography

Heparin affinity chromatography has been used to extract minor protein components from two whey protein isolates (WPIs), one produced by ion-exchange chromatography (IEC-WPI) and the second by microfiltration/ultrafiltration (MF/UF-WPI). Only 1–13% of the major whey proteins bound to the heparin column. However, insulin-like growth factor-I (IGF-I), transforming growth factor-beta2 (TGF-β2) and lactoferrin were concentrated by factors of 24–38, 10–0 and 32–93, respectively, in the fraction eluted with 0.5 m NaCl from IEC-WPI and MF/UF-WPI. Two-dimensional gel electrophoresis of this fraction from IEC-WPI (but not from MF/UF-WPI) also revealed the presence of minor proteins, including heart fatty acid-binding protein, transthyretin, β2-microglobulin, and angiogenin. These observations suggest that heparin affinity chromatography can be used not only to separate the major proteins contained in some WPIs, but also to concentrate the minor cationic proteins and some milk growth factors.