title: Exopolysaccharide production by Streptococcus thermophilus SY: production and preliminary characterization of the polymer.
abstract: OBJECTIVE
  To evaluate the effect of yeast extract (YE) concentration, temperature and pH on growth and exopolysaccharide (EPS) production in a whey-based medium by Streptococcus thermophilus SY and to characterize the partially purified EPS.
  
  
  RESULTS
  Factorial experiments and empirical model building were used to optimize fermentation conditions and the chemical composition, average molecular weight (MW) and rheological properties of aqueous dispersions of the EPS were determined. Exopolysaccharide production was growth associated and was higher (152 mg l(-1)) at pH 6.4 and 36 degrees C with 4 g l(-1) YE. High performance size exclusion chromatography of the partially purified EPS showed two peaks, with a weight average MW of 2 x 10(6) and 5 x 10(4), respectively. The EPS was a heteropolysaccharide, with a glucose : galactose : rhamnose ratio of 2 : 4.5 : 1. Its water dispersions had a pseudoplastic behaviour and showed a higher viscosity of xanthan solutions.
  
  
  CONCLUSIONS
  The fermentation conditions and some properties of an EPS produced by Strep. thermophilus, a dairy starter organism, were described.
authors.affiliation: Dipartimento di Biologia, Difesa e Biotecnologie Agro-forestali, Università della Basilicata, Potenza, Italy. Aricciardi@unibas.it
authors.forename: A
authors.initials: A
authors.lastname: Ricciardi
authors.forename: E
authors.initials: E
authors.lastname: Parente
authors.forename: M A
authors.initials: MA
authors.lastname: Crudele
authors.forename: F
authors.initials: F
authors.lastname: Zanetti
authors.forename: G
authors.initials: G
authors.lastname: Scolari
authors.forename: I
authors.initials: I
authors.lastname: Mannazzu
mesh_terms: D001704:Biopolymers / Q000096:biosynthesis / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis* / Q000737:chemistry; D013291:Streptococcus / Q000201:enzymology* / Q000254:growth & development; D013696:Temperature; D015003:Yeasts
chemical_list: D001704:Biopolymers; D011135:Polysaccharides, Bacterial; C098632:exopolysaccharide, Streptococcus