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