Probing thermal stability of the β-lactoglobulin–oleic acid complex by fluorescence spectroscopy and molecular modeling

• Conformational changes of β-lactoglobulin–oleic acid were analyzed.
• The emissive properties indicated unfolding at temperatures higher than 70 °C.
• The most significant increase of accessible surface area was identified at Tyr99 and Tyr102.
• No contact between Ile56 or Lys60 and the fatty acid could be identified at 85 °C.

Bovine β-lactoglobulin is able to interact with different bioactive compounds, thus being an important candidate in the development of delivery systems with improved functionality.The heat induced changes in the β-lactoglobulin–oleic acid complex were examined by means of fluorescence spectroscopy and molecular modeling techniques.Fluorescence spectroscopy results indicated a rigid protein structure in the temperature range 25–70 °C, whereas at temperatures over 75 °C, the rearrangements of the polypeptide chains led to higher exposure of hydrophobic residues. The most significant increase of the accessible surface area with temperature increase was identified in case of Tyr99 and Tyr102. The phase diagram method indicated an all or none transition between two conformations. Due to conformational changes, no contact between Ile56 or Lys60 and the fatty acid could be identified at 85 °C, but new non-bonding interaction were established with Ile12 and Val15.The results obtained in this study provide important details about thermal induced changes in the conformation of β-lactoglobulin–oleic acid complex. Significant conformational changes were registered above 75 °C, suggesting the possibility of obtaining highly functional complexes between whey proteins and natural unsaturated fatty acids.

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