Structural and Biochemical Characterization of Levan Produced by Gluconobacter cerinus UELBM11 Isolated from Brazilian Grapes

Acetic acid bacteria (AAB) are versatile organisms that catalyze the conversion of a wide range of carbon sources into biomolecules of great industrial interest. In this study, we exploited the ability of Gluconobacter spp. to synthesize levans. Among the isolated strains, Gluconobacter cerinus UELBM11 produced approximately 14.0 g L-1 of levan under non-optimized conditions. Gas chromatography-mass spectrometry (GC-MS), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR) analyses confirmed that levan obtained from G. cerinus UELBM11 consisted of a β-(2→6)-D-fructose backbone with some β-(2→1) ramifications. The average molecular weight (Mw) of the purified levan was 8.78 × 105 Da. Thermogravimetric/differential thermogravimetric (TGA/DTG) analysis indicated high thermal stability, with the maximum decomposition rate observed at 227.44 °C. Scanning electron microscopy (SEM) revealed a microporous morphology, and the antioxidant activity assays demonstrated that levan had a high scavenging capacity of 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and hydroxyl radicals. Therefore, it has been demonstrated the levan produced by G. cerinus UELBM11 is a promising natural antioxidant and, owing to its microporosity and excellent thermal properties and stability, is a potential candidate as an additive in cosmetics, pharmaceuticals, and food products.