Methods: A chemically defined medium (CDM) was used as basal medium to study factors affecting growth and EPS production under anaerobic condition with various cultural treatments. Fermentation experiments at different factors were carried out by individually supplementing dextrose, maltose, lactose, sucrose and fructose. Initial concentration of carbon source (2, 5, 10, 15, 20 and 25 g/l) was compared. Initial pH of CDM was adjusted to 4.3, 5.5, 6.8, 7.0 and 7.5. Incubation temperature was compared among 30, 35, 37, 42 and 45 °C. Fermentation time was incubated for 6, 12, 24, 48, 60, 72 and 84 h. Growth was measured by gravimetric method. EPS was determined by measuring dry weight. EPS was precipitated by two volumes of cold ethanol. Precipitates were collected by centrifugation and resuspended in one volume of demineralized water. After precipitation, pellets were dried at 55°C.
Results: Factors found to affect EPS production in CDM were conducted. Growth and EPS were associated which were greatest during the stationary phase. Both lactose and sucrose proved to be the effective carbon sources for EPS production, however sucrose gave higher concentration of EPS (3.56±0.06 g/l) whereas dextrose and maltose were more effective than others for growth supporting. Initial concentration of sucrose (25 g/l) gave the highest EPS concentration at 4.13±0.23 g/l. The initial pH of CDM was 7.5. Incubation temperature was moderate temperature (35-37°C). High yield of EPS was shown at duration time of 48 h. Factors increased growth about 2.74 folds from 2.36±0.04 to 6.46± 0.25 g/l whereas 4.3 folds for EPS concentration from 2.2±0.2 to 9.53±0.21 g/l.
Conclusions: EPS production from L. paracasei SD1 was growth-associated. The optimal condition for growth and EPS was 25g/l sucrose, pH 7 incubated at 35-37°C for 48 h.