Isolation and identification,fermentation process optimization and antioxidant activity of a high exopolysaccharides-producing leuconostoc sp.from sugar beet molasses

ZHANG Han; CHEN Haijun; LONG Xiaoyu; ZHAO Shuna; WEI Xuejun; WEI Guokun; SHEN Guanghui

doi:10.12187/2024.03.002

Abstract：The objective of this study was to screen lactic acid bacteria strains with high exopolysaccharides production potential from sugar beet molasses.The taxonomic identification and growth characteristics of a lactic acid bacteria strain M1 with high exopolysaccharides-producing capacity isolated from sugar beet molasses were investigated.Furthermore,the exopolysaccharides fermentation parameters using sugar beet molasses as an alterna-tive carbon source to sucrose were optimized using a single-factor experiment and response surface methodology based on Box-Behnken design.Moreover,antioxidant activity of the harvested crude exopolysaccharides were eval-uated.The results showed that strain M1 was taxonomically classified as Leuconostoc suionicum.The growth profile of L.suionicum M1 indicated a lag phase of 2 hours,an optimal temperature of 35℃,a favorable pH value of 8.0,and a remarkable tolerance to sucrose concentrations up to 60％.The optimal medium for exopolysaccharides pro-duction consisted of 300 g/L sugar beet molasses,20.0 g/L yeast extract,15.0 g/L K2HPO4·3H2O,0.2 g/L MgSO4·7H2O,0.01 g/L NaCl,0.01 g/L CaCl2·2H2O,0.01 g/L MnSO4·4H2O,0.01 g/L FeSO4·7H2O.The maximum exopolysaccharides yield of 39.1 g/L was achieved under the following conditions:loading volume 200 mL/250 mL,inoculum size 5％,initial pH value 8.1,fermentation temperature of 38.5℃ and fermentation period 41.1 h.The exopolysaccharides produced by strain M1 exhibited significant antioxidant activities,with quenching capacities of 70.25％for DPPH radicals,47.16％for·OH radicals,35.92％for ABTS+radicals and 0.42 for Fe3+total reducing force at a concentration of 6.0 mg/mL.Strain M1 was capable of producing exopolysac-charides with antioxidant activity using sugar beet molasses,and could be used as a promising candidate for the bioconversion of sugar beet molasses into functional exopolysaccharides products.