Papain Adsorption on Latex Particles: Charging, Aggregation, and Enzymatic Activity.

The effect of papain adsorption on the surface charge properties and aggregation mechanism of sulfate-functionalized polystyrene latex particles was studied. The positively charged enzyme possessed a high affinity to the oppositely charged particles, giving rise to charge neutralization and charge reversal at appropriate papain concentrations. The tendency in the particle aggregation rates at different enzyme doses revealed that the colloidal stability of the samples is governed by interparticle forces of electrostatic origin. The aggregation mechanism was qualitatively described within the classical DLVO theory, and unstable dispersions were detected near the charge neutralization point, while particle aggregation was not observed at low and elevated papain concentrations. The relatively high dispersion stability of the bare latex particles was maintained upon the formation of an enzyme layer on the surface, and the obtained latex-papain composite showed notable resistance against salt-induced aggregation. Remarkable hydrolytic and antioxidant activities of the immobilized enzyme were observed in probe reactions; therefore, the obtained hybrid can be considered as a multifunctional biocatalytic system with great promise in applications in industrial manufacturing processes.