Physicochemical and functional characterization of mannan exopolysaccharide from Weissella confusa MD1 with bioactivities.

The present study focused on production, optimization and characterization of exopolysaccharide (EPS) from Weissella confusa MD1. The purified EPS MD1 was also evaluated for in vitro biological activities. The maximum yield of EPS (10.07 ± 0.32 g/L) was obtained with optimized culture conditions of 35 °C at pH 6.5 for 36 h with 4% (w/v) galactose and 1% (w/v) ammonium nitrate supplemented in MRS broth. The crude EPS was purified with diethylamino ethanol-Sepharose Fast Flow column and Sephadex-G 75 column. The physicochemical and functional characterization of the EPS was done by high-performance thin-layer chromatography (HPTLC), high-performance gel permeation chromatography (HPGPC), fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), thermo gravimetric and differential scanning calorimetric (TG-DSC) analysis, x-ray diffraction (XRD) and scanning electron microscopy (SEM). HPGPC analysis showed molecular weight of purified EPS MD1 as 2.909 KDa. Monosaccharide analysis showed that EPS was a novel mannan with mannose as the only monomeric unit present, suggesting EPS to be a homopolysaccharide containing → 6) α-Man p (1 → linkages. Microstructure studies by SEM showed MD1 EPS has globular and porous structure. The purified EPS MD1 exhibited higher thermal stability having degradation temperature around 267.74 °C with melting enthalpy value (Δ H) of 337.7 J/g. The EPS showed promising antioxidant activities with excellent antibiofilm activity against Staphylococcus aureus, Listeria monocytogenes, Salmonella enterica and Salmonella typhi. These striking physicochemical characteristics features and bioactivities of EPS would serve as potential candidate in food processing industry to be used as food adjunct in foods with health benefits. This is the first study reporting a mannan homopolysaccharide from Weissella sp. to be structurally characterized.