Characterization of new exopolysaccharides produced by coculturing of L. kefiranofaciens with yoghurt strains.

This project was designed to study the coculturing affect of exopolysaccharide (EPS) producing strains Lactobacillus kefiranofaciens (L.k) ZW3, with non EPS producing strains L. bulgaricus (L.b) and Streptococcus thermophilus (S.t) in three different combinations: L.k+L.b, L.k+S.t, and L.k+L.b+S.t. FTIR analysis revealed presence of strong stretch in regions of 3400, 2900 and 1647cm(-1) which is characteristic of a typical polysaccharide. Co-cultured EPSs were composed of glucose, galactose, arabinose and xylose; and their sugar compositions were different from ZW3 polysaccharide that was mainly composed of gluco-galactan. Peak temperature for L.k+L.b, L.k+S.t, L.k+S.t+L.b and ZW3 polymers were 90.59, 87.61, 95.18 and 97.38°C, respectively. Thermal analysis revealed degradation temperature of 326.44, 294.6, 296.7 and 299.62°C for L.k+L.b, L.k+S.t, L.k+S.t+L.b and ZW3 polymers, respectively. SEM and AFM analysis divulged that three cocultured EPSs had different surface morphology than ZW3 polymer. Since co-cultured polymers have different structure than the polymer produced exclusively by EPS producing strain, it can be safely concluded from the study that co-culturing can be one way to change the structure of polymers. Coculturing of L. kefiranofaciens with non-EPS producing strains resulted in yoghurt with increased viscosity and delayed syneresis.