The effect of calcium and magnesium on the interaction between β-lactoglobulin and carotenoids from sea buckthorn berries.

β-Lactoglobulin has been shown to interact with carotenoids from sea buckthorn berries. However, previously, no studies have taken into account the effect of calcium and magnesium on the β-lactoglobulin-carotenoids complex. This study aims to determine the effect of calcium and magnesium on the interaction between β-lactoglobulin and carotenoids from sea buckthorn berries extract, during heating from the perspective of deepening interaction mechanisms as prerequisites for micro- and nanoencapsulation. Phase diagram, intrinsic fluorescence spectra, quenching experiments and synchronous spectra were employed to acquire information regarding the conformation of protein in the presence of calcium chloride and magnesium chloride. Intrinsic fluorescence data showed that, between 25°C and 60°C, the presence of calcium chloride in the complex favoured the movement of tryptophan residues to domains located at the protein-water interface, while magnesium chloride favoured the burial of tryptophan residues. Higher temperatures generated blue shifts regardless of which salt was present, suggesting exposure of tryptophan residues to the hydrophobic core of the protein. Extrinsic fluorescence intensity of the non-heat-treated complex with magnesium chloride was significantly higher (P < 0.01) than of the complex with calcium chloride, suggesting that 1-anilino-8-naphtalenesulphonic acid was bound to a higher proportion of the β-lactoglobulin-carotenoids complex. Calcium chloride increased extrinsic fluorescence to a greater extent than magnesium chloride at temperatures above 70°C and was related to small structural changes induced by preheating β-lactoglobulin.