Abstract

In the present study, a laccase gene (BaLc) from a lignin degrading bacterium, Bacillus atrophaeus, has been cloned and expressed in Escherichia coli. The optimal catalytic activity of the protein was achieved at 5.5 pH and 35°C temperature, measured by oxidation of ABTS. The Km and Vmax values were determined as 1.42 mM and 4.16 μmole/min, respectively. To achieve the enzyme recovery, the biocatalyst (BaLc) was covalently attached onto the functionalized iron magnetic-nanoparticles. The nanoparticles were characterized by zeta-potential and FTIR analyses. The immobilized BaLc enzyme was physico-kinetically characterized, exhibiting retention of 60% of the residual activity after ten reaction cycles of ABTS oxidation. The immobilized biocatalyst system was tested for its biotechnological exploitability in plant juice processing, achieving 41–58% of phenol reduction, 41–58% decolorization, 50–59% turbidity reduction in the extracts of banana pseudo-stem and sweet sorghum stalk, and apple fruit juice. This is the first study to demonstrate the use of nanoparticle- laccase conjugate in juice clarification. The findings suggest that B. atrophaus laccase is a potential catalytic tool for plant juice bioprocessing activities.

• Keywords: laccase; Bacillus atrophaeus; immobilization; magnetic nanoparticles; fruit juice clarification