Combined Effects of Temperature and Medium Composition on Exopolysaccharide Production by Lactobacillus rhamnosus RW-9595M in a Whey Permeate Based Medium

The effects of temperature (22-42 °C), whey permeate concentration (WP, 1.6-8.4%), and supplementation level with yeast nitrogen base (YNB, 0-2.0%) on exopolysaccharide (EPS) production was studied during 20 pH-controlled (pH = 6.0) batch cultures with Lactobacillus rhamnosus RW-9595M, using a central composite design (CCD). The EPS production was measured using both the conventional method based on ethanol precipitation of EPS and a new ultrafiltration (UF) method. EPS production was not growth-associated for high temperatures (32—42 °C) and WP concentrations (7.0-8.4%). In contrast, at suboptimal temperature (22-26 °C), EPS production was growth-associated. Maximal EPS production measured with the UF method was approximately 2-fold higher than those measured with the conventional method and varied from 125 to 477 mg/L. This parameter was significantly influenced by WP and YNB*WP interaction, whereas ANOVA for maximal EPS production measured by the conventional method did not show significant factor effects. EPS volumetric productivities varied from 3.0 to 16.4 mg EPS/Lʹh. YNB supplementation did not promote cell growth but did increase EPS production at high WP concentrations. Our data indicate the potential of L. rhamnosus RW-9595M for producing EPS in a supplemented WP medium and suggest that this production could be further increased by the addition of a growth-limiting nutrient in the medium.