Binding of carotenoids to milk proteins: Why and how

Caseins and whey proteins have great potential for interacting with carotenoids due to their binding sites with hydrophobic domains. Even if a neglected amount of carotenoids is naturally bound to milk proteins, the complexation of these molecules has been proven to be an efficient approach for increasing carotenoid solubility and protection against oxidation, for instance. This review compiled the updated research progress in this field, pointing out all the benefits associated with the interaction between carotenoids and milk proteins and the challenges of characterizing the mechanisms involved in the binding. The impact of temperature, pH, and ionic strength, and the intrinsic characteristics of milk proteins and carotenoids on their binding affinity were reviewed. The main analytical methods applied for the characterization of the binding mechanism were comparatively discussed. The binding of carotenoids to milk proteins is a promising strategy for the development of functional fat-free foods enriched with these bioactive molecules. However, the practical challenges to investigate the interaction between milk proteins and this low-water soluble group of molecules must be considered. Despite being affected by many factors, a binding constant of about 104 M−1 and moderate affinity between carotenoids and milk proteins were frequently reported. Finally, promising techniques and future challenges for this scientific field were addressed. Besides research groups focused on elucidating the mechanism behind the binding between carotenoids and proteins, the scope covered by this review may also interest those involved in the development of healthier formulated food products.