Conjugation of polyphenols prevents lactoferrin from thermal aggregation at neutral pH

• Lactoferrin (LF) was covalently modified by polyphenol (chlorogenic acid (CA) or EGCG) in alkaline solution.
• Lactoferrin-polyphenol conjugates were thermal stable at pH 7.0 and 0–200 mM NaCl.
• The modification lowered the surface hydrophobicity and increased the magnitude of ζ-potential of LF.
• Repulsive steric interactions were the dominant mechanism controlling lactoferrin aggregation.
• LF-CA conjugate exhibited better thermal stability than LF-EGCG conjugate.

Because of the aggregation and/or gelation of lactoferrin (LF) occurred during thermal treatment, its application is limited in food products. The present study was focused on the effect of covalently binding polyphenols on the heat-induced structural changes of LF in a neutral aqueous solution. LF, LF-chlorogenic acid (CA) and LF-epigallocatechin-3-gallate (EGCG) mixtures and conjugates in sodium phosphate buffer were heated between 50 °C and 90 °C for 20 min with or without NaCl (100–200 mM). The mechanism for the inhibition of LF aggregation during thermal treatment was elucidated by multispectral and physicochemical methods. Fourier transform infrared and circular dichroism spectroscopies suggested that a higher degree of changes in the secondary structure occurred for LF than LF-polyphenol conjugates. According to physicochemical analysis, the conjugation of polyphenols to LF increased the magnitude of ζ-potential and reduced the surface hydrophobicity, resulting in a lower turbidity during heat treatment. In addition, after heating at 90 °C for 20 min, a greater extent of aggregation was found in LF than LF-polyphenol conjugates by atomic force microscope. These results revealed that LF could generate aggregates at neutral pH after heating and the conjugation of polyphenols prevented LF from thermal aggregation by steric hindrance and electrostatic repulsion.

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