Decreased formulation pH and protein preheating treatment enhance the interaction, storage stability, and bioaccessibility of caseinate-bound lutein/zeaxanthin

Heat treatment and pH are crucial factors in the formulation and processing of food and beverages; thus, a thorough understanding of the impact of these factors on the interactions between bioactive constituents and proteins is essential to developing effective protein-based delivery systems. This study explores the influences of pH (ranged from 1.5 to 7.5) and preheating treatment on the characteristics of caseinates-lutein (LU)/zeaxanthin (ZX) complexes and evaluates the potential application of caseinates as protective carriers in xanthophyll-fortified beverages. The properties and interactions of caseinates and two xanthophylls were systematically investigated utilizing a range of spectroscopic techniques, including ultraviolet-visible (UV-Vis) spectroscopy, dynamic light scattering (DLS), fluorescence spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. Caseinates were bound to LU/ZX with a binding constant of the order 10⁵ M^-1. Furthermore, ZX exhibited a higher affinity for caseinates than LU. In particular, the decreased pH level of complex formulation and the preheating of caseinates at 85 °C strengthened the binding affinity between LU/ZX and caseinates. The caseinate-LU/ZX complexes effectively improved the chemical stability of LU/ZX and achieved a bioaccessibility rate of over 70 %. This study provides a guide for developing commercially available xanthophyll-fortified beverages and further expanding the application of caseinates as encapsulation carriers for extremely hydrophobic nutrients in the food industry.