Relationships between conformation of beta-lactoglobulin in solution and gel states as revealed by attenuated total reflection Fourier transform infrared spectroscopy

Attenuated total reflection Fourier transform infrared spectroscopy (ATR FT -IR) has been used to compare the structure of beta-lactoglobulin, the majo r component of whey proteins, in solution and in its functional gel state. To induce variation in the conformation of beta-lactoglobulin under a set o f gelling conditions, the effect of heating temperature, pH, and high press ure homogenization on the conformation sensitive amide I band in the infrar ed spectra of both solutions and gels has been investigated. The results sh owed that gelification process has a pronounced effect upon beta-lactoglobu lin secondary structure, leading to the formation of intermolecular hydroge n-bonding beta-sheet structure as evidenced by the appearance of a strong b and at 1614 cm(-1) at the expense of other regular structures. These result s confirm that this structure may be essential for the formation of a gel n etwork as it was previously shown for other globular proteins. However, thi s study reveals, for the first time, that there is a close relationship bet ween conformation of beta-lactoglobulin in solution and its capacity to for m a gel. Indeed, it is shown that conditions which promote predominance of intermolecular beta-sheet in solution such as pH 4, prevent the formation o f gel in conditions used by increasing thermal stability of beta-lactoglobu lin. On the basis of these findings, it is suggested that by controlling th e extent of intermolecular beta-structure of the protein in solution, it is possible to modify the ability of protein to form a gel and as a consequen ce to control the properties of gels. (C) 1999 Elsevier Science B.V. All ri ghts reserved.