The yield of exopolysaccharide (EPS) produced by Streptococcus thermophilus 05-34 reached up to
250 mg/L under the optimal fermentation condition, which was 4.2-fold higher than that produced under
the non-optimal fermentation condition. Structure analysis showed that EPS produced under the optimal
fermentation condition was composed of galactose and glucose in a molar ratio of 1.0:0.8. This EPS was
with a molecular mass of 4.7 105 Da, which was increased by 9 times compared with that in the
non-optimal fermentation condition, while monosaccharide composition did not change. Furthermore,
real-time quantitative PCR showed that the transcription level of epsC, which is responsible for chainlength
determination, was up-regulated by 2.7-fold, suggesting that the increased molecular mass of
EPS was resulted from improving polymerization degree of monosaccharide. These findings
demonstrated that the optimized fermentation condition can improve EPS molecular mass, and may consequently
modify the rheological properties of EPS.