Partial characterization and dynamics of synthesis of high molecular mass exopolysaccharides from Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus |
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Authors: | Z L Urshev Z P Dimitrov N S Fatchikova I G Petrova D I Ishlimova |
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Institution: | (1) LB Bulgaricum Plc., R&D Center, 12A Malashevska str., Sofia, 1202, Bulgaria |
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Abstract: | Exopolysaccharide (EPS) preparations from Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus) strains LBB.B26 and LBB.B332 and Streptococcus thermophilus strains LBB.T54 and LBB.T6V were characterized using ion-exchange chromatography and gel filtration. All four preparations
contained a neutral EPS with molecular mass in the range of 1.3−1.6 × 106 Da (HMM-EPS). The EPS preparations from the two L. bulgaricus strains also contained an acidic low molecular mass EPS fraction (LMM-EPS) comprising from 10% to 34% of the total EPS yield.
HMM-EPS preparations were subjected to High Pressure Liquid Chromatography (HPLC) analysis of monomer sugars after complete
hydrolysis. Glucose, galactose and/or rhamnose in different ratios proved to be the principal sugars building the HMM-EPS
from all four strains. The chemical composition of HMM-EPS was strictly strain-specific. The LMM-EPS contained galactose.
The viscosifying properties of the four different HMM-EPS varied greatly with intrinsic viscosity in the range from 0.26 (strain
B26) to 2.38 (strain T6V). For 24 h the two L. bulgaricus strains accumulated more HMM-EPS in milk (>70 mg l−1) than S. thermophilus strains T54 and T6V (<30 mg l−1), but maximal yields were reached earlier with cocci (8 h) than with rods (16–24 h). The contribution of HMM-EPS production
to increased viscosity of fermented milk was demonstrated for all of the tested strains grown as monocultures or as mixed
yogurt starters compared to non-EPS producing S. thermophilus LBB.A and poor EPS-producer L. bulgaricus LBB.B5. The extent of increased viscosity was strongly dependent on the nature of the produced HMM-EPS, rather than simply
on polymer yield. |
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Keywords: | Exopolysaccharide (EPS) Lactobacillus delbrueckii ssp bulgaricus Streptococcus thermophilus |
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