A mannose-rich exopolysaccharide from Weissella cibaria SK01: Purification, characterization, antibiofilm, anticancer, and physicochemical properties.

Among lactic acid bacteria (LAB) strains isolated from minced beef, an effective exopolysaccharide (EPS)-producing bacterium was identified using 16S rRNA gene sequencing as Weissella cibaria SK01. A distinctive EPS, designated EPS-SK01, was produced in relatively high yield (2.79 g/L) and purified to apparent homogeneity by consecutive chromatographic procedures. Structural characterization using monosaccharide composition analysis, FTIR, GPC, and one-dimensional NMR revealed that EPS-SK01 is mainly composed of α-linked mannose residues, necessitating further validation through advanced structural analyses. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses revealed a hierarchical, porous-like architecture characterized by multiscale surface features ranging from nanoscale to microscale. Thermal investigations (DSC, DTG, and TGA) revealed well-defined thermal transitions and significant thermal stability, with a principal decomposition event occurring at around 273 °C. EPS-SK01 exhibited favorable physicochemical characteristics, such as high solubility, shear-thinning rheological properties, and efficient emulsifying and foaming abilities. EPS-SK01 showed concentration-dependent antioxidant activity (DPPH IC50 = 22.95 mg/mL) and antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) (MIC of 5 mg/mL). Moreover, it could restrain MRSA biofilm formation by 55.3 ± 1.7%, which was associated with a significant reduction in the expression of biofilm-related genes (icaA, icaD, and srtA) and quorum-sensing regulatory genes. In MCF-7 breast cancer cells, EPS-SK01 exhibited dose-dependent antiproliferative activity with an IC50 value of 1313 μg/mL, while maintaining negligible cytotoxicity toward normal L929 fibroblasts. Taken together, these findings identify EPS-SK01 as a microbial exopolysaccharide with a distinct structure and biological activity, underscoring its potential for use in the fermented food processing industry.