Enhancing antimicrobial activity in unbleached kraft pulp using laccase and phenolic compounds

Abstract

Unbleached kraft pulp fibers were reacted with laccase in the presence of different phenolic compounds (isoeugenol, butyl p-hydroxybenzoate, p-coumaric acid, and ferulic acid) in order to confer them with new properties. After the enzymatic stage, antimicrobial tests demonstrated that the handsheets formed from the laccase/phenolic-treated pulp showed a greater efficacy against Gram-positive and Gram-negative bacteria compared to handsheet paper treated only with laccase and a control. Laccase in the presence of butyl p-hydroxybenzoate produced handsheets with the most significantly enhanced bactericidal effect. An analysis of scanning electron microscope images of the treated kraft pulps increased kappa numbers and surface features of the fibers. The reduction in the absolute value of the zeta potential of the pulps indicates that the phenolic compounds produce chemical cross-linking within the fiber surface. X-ray photoelectron spectroscopy shows that the lignin content of the pulp fiber surface increased after adding the laccase and phenolic compounds.