Growth factors from bovine milk and colostrum: composition, extraction and biological activities

EGF, BTC, IGF-I, IGF-II, TGF-beta 1, TGF-beta 2, FGF1 and 2, and PDGF are the main growth factors present in bovine milk and colostrum. All of these growth factors are also found in human milk but at a lower concentration. The various compositional data reported in the literature vary greatly but it is evidenced that the day of lactation has the most important effect. Milk growth factors are characterized by a neutral to alkaline isoelectric point (pI) and a molecular mass between 6400 g.mol(-1) and 30000 g.mol(-1). However, many of the growth factors are in a latent form, bound to high-molecular-mass proteins. Milk growth factors are resistant generally to pasteurization but disulfide reducing agents have been found to inactivate some species such as TGF-beta's. The published data on bioavailability of milk growth factors are somewhat contradictory but it is generally accepted that they are resistant to gastric digestion and they can exert local and systemic effects on the gastrointestinal tract. Cation-exchange chromatography has been widely used for the extraction of milk growth factors because of the basic nature of these molecules. Membrane separations such as microfiltration (MF) have also been used successfully for the extraction of immunoglobulins and of some growth factors from colostrum, while ultrafiltration (UF) was successful only at separating IGF-I and IGF-II in whey. Milk growth factor extracts have been developed for various applications such as treatment of gastrointestinal disorders and skin diseases, wound healing, and induction of oral tolerance.