Solubilization of a Lipophilic Compound in Highly Concentrated Saccharide Solutions Containing Protein

Abstract

Solubilization of a lipophilic compound in highly concentrated saccharide solutions containing protein was studied by measuring the amount of the lipophilic compound solubilized, the surface hydrophobicity of protein, the line width of the water signal in 1H-NMR spectra, and the unfreezable water content using a differential scanning calorimeter (DSC). The solubilizing ability, which was shown by the amount of solubilized p-dimethylaminoazobenzene (DMAB), increased with increasing saccharide concentration in the aqueous system. The effects of different saccharides on the solubilizing ability of a saccharide and bovine serum albumin (BSA) mixture decreased in the following order: sucrose > maltose > fructose > glucose. The solubilizing ability of a saccharide and BSA mixture was higher about 4–5 times than that of saccharide only. A good correlation was observed between the solubilizing ability of a saccharide and BSA mixture and the surface hydrophobicity of BSA. The line width of the water signal in 1H-NMR spectrum and the unfreezable water content using DSC, that is, the bound water content in saccharide solution containing BSA increased with increasing saccharide concentration. From these results, a large amount of DMAB solubilized in a highly concentrated saccharide solution containing BSA would be attributed to the hydrophobicity interaction between BSA and DMAB due to the surface hydrophobicity of BSA which increased with increasing bound water content.