Characterization of milk proteins–lutein complexes and the impact on lutein chemical stability

• Lutein doesn’t affect the secondary structure of milk proteins.
• Degradation of lutein was inhibited by binding with milk proteins.
• Sodium caseinate is a better choice in improving lutein’s stability.

In this study, the interaction of WPI (whey protein isolate) and SC (sodium caseinate) with hydrophobic lutein was investigated through UV–vis spectroscopy and circular dichroism (CD) as well as fluorescence. The effects on lutein’s chemical stability were also examined. The decrease of turbidity of lutein suggested that lutein’s aqueous solubility was improved after binding with milk proteins. CD analysis indicated lutein had little impact on the secondary structures of both proteins. Different preparation methods have significant impacts on the binding constant. Fluorescence results indicated that WPI and SC interact with lutein by hydrophobic contacts. Milk proteins have protective effects on lutein against oxidation and decomposition, and SC showed better capability in protecting lutein from oxidation than WPI during 16 days storage. The lutein’s chemical stability was increased with increasing of proteins concentration. The results indicated that milk proteins may act as effective carriers for lipophilic nutraceuticals.