Enhancement of antioxidant activity of levan through the formation of nanoparticle systems with metal ions

Levan, a natural polymer, is widely used in biomedical applications, such as antioxidants, anti-inflammatory, and anti-tumor. The present study aimed to enhance the antioxidant activity of levan by combining it with various metal ions in the nanoparticle (NP) system. Levansucrase encoding gene from Bacillus licheniformis BK1 has been inserted into an expression vector and the obtained recombinant was labeled as Lsbl-bk1 (accession number MF774877.1). That enzyme was used for in vitro levan synthesis in 12% (w/v) sucrose as a substrate and about 4.28 mg/mL of levan was obtained. Levan-based metal ion NPs were synthesized using the coprecipitation method. In the production of NPs, levan acts as a reducing and stabilizing agent. Four types of levan-based metal ion NPs were synthesized, namely, levan–Fe(2+) NPs, levan–Cu(+) NPs, levan–Co(2+) NPs, and levan–Zn(2+) NPs. The transmission electron microscopy (TEM) technique was applied to visualize the size and shape of the synthesized levan–metal NPs. All levan-based metal ion NPs have a particle size of less than 100 nm, and even levan–Cu(+) and levan–Zn(2+) have particle sizes less than 50 nm. Levan–Fe(2+) NPs and levan–Cu(+) NPs exhibited prominent antioxidant activity with an inhibition level of up to 88% and 95%, respectively. And the inhibition level of two metal ion NPs had about 33%–40% higher antioxidant activity compared with the inhibition level of levan only. The two levan–metal ion NPs, therefore, have future prospects to be developed as the new formulation for the antioxidant drugs.