HS-protein associates in the aqueous/oil system: Composition and colloidal properties

Abstract

Tritium-labeled Leonardite humic acids (HA) and two types of globular proteins lysozyme from chicken egg white and human serum albumin were used to study its interference in the aqueous/oil system. p-Xylene was chosen as an oil phase. Tritium was introduced in each compound by thermal activation method. The studies of liquid/liquid systems were carried out by scintillation phase technique developed for compound mixtures. The reaches were performed for fixed concentration of protein (0.1 mg/mL for lysozyme and 0.06 mg/mL for albumin). HA concentration was varied from 0.2 to 50 μg/mL. It was found that the increase of ionic strength of an aqueous phase leads to the respective growth of the distribution coefficient and adsorption of HA. Both the distribution coefficient and the adsorption of HA were increased in presence of lysozyme (positively charged protein under the experimental conditions) and decreased in presence of albumin (negatively charged protein under the experimental conditions). The distribution coefficient of lysozyme was also increased in protein-HA mixture compared to individual protein. However, its amount in the adsorption layer was decreased with HA concentration growth that is explained by the formation of protein-HA hydrophobic associate that precipitates from the solution. For the first time, the quantitative composition of HA-lysozyme precept was determined for a wide range of HA concentrations. The interference of HA and albumin revealed the increase in solubility of HA-protein associate in the aqueous phase. The experimental data revealed that protein encapsulation by humic substances is controlled by both electrostatic and hydrophobic interactions.