Optimization, fractional characterization, and antioxidant potential of exopolysaccharides from Levilactobacillus brevis NCCP 963 isolated from "kanji"

Abstract

A novel exopolysaccharide (EPS) was obtained from Levilactobacillus brevis NCCP 963 isolated from a black carrot drink named "kanji". The culture conditions for maximum EPS yield were explored by the Plackett-Burman (PB) design and response surface methodology (RSM) along with the fractional characterization and antioxidant potential of EPSs. The PB design screened out five significant factors, namely, glucose, sucrose, tryptone, CaCl₂, and di-potassium phosphate out of eleven independent factors. The RSM indicated glucose and CaCl₂ as significant factors in EPS production and a maximum EPS production of 968.89 mg L^-1 was obtained at optimized levels of 10.56% glucose, 9.23% sucrose, 0.75% tryptone, 0.446% CaCl₂, and 0.385% K₂HPO₄. A R² value above 93% indicates higher variability, depicting the validity of the model. The obtained EPS has a molecular weight of 5.48 × 10⁴ Da and is a homopolysaccharide in nature with glucose monosaccharides. FT-IR analysis showed significant band stretching of C-H, O-H, C-O and C-C and indicated the β-glucan nature of EPSs. The comprehensive antioxidant investigation showed significant in vitro DPPH, ABTS, hydroxyl, and superoxide scavenging capacity with EC₅₀ values of 1.56, 0.31, 2.1, and 6.7 mg mL^-1 respectively. Curd formation from the resulting strain prevented syneresis.