Exopolysaccharide production by Streptococcus thermophilus SY: production and preliminary characterization of the polymer

Dipartimento di Biologia, Difesa e Biotecnologie Agro-forestali, Università della Basilicata, Potenza, Italy.
Journal of Applied Microbiology (Impact Factor: 2.39). 02/2002; 92(2):297-306. DOI: 10.1046/j.1365-2672.2002.01487.x
Source: PubMed

ABSTRACT 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.
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.
The fermentation conditions and some properties of an EPS produced by Strep. thermophilus, a dairy starter organism, were described.

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Available from: Flavio Zanetti, Oct 08, 2014
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    • "These complex polymers can also contain acetylated amino sugar moieties, as well as noncarbohydrate constituents such as phosphate, lactate, acetate and glycerol (De Vuyst & Degeest, 1999; De Vuyst et al., 2001; Ruas-Madiedo et al., 2002; Girard & Schaffer-Lequart, 2007). The composition of the bacterial EPS varies with the type of microorganism (Vaningelgem et al., 2004; Panhota et al., 2007), nutrient availability (De Vuyst & Degeest, 1999; Ricciardi et al., 2002), growth phase and environmental conditions (Fischer et al., 2003; Bahat-Samet et al., 2004). However, the mechanisms involved in the synthesis of EPS seem to be relatively conserved for Gram-negative and Gram-positive bacteria (De Vuyst et al., 2001; Jolly & Stingele, 2001; Laws et al., 2001; Sutherland, 2001; Welman & Maddox, 2003; Whitfield, 2006). "
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    • "Earlier studies revealed that though EPS synthesis by thermophilic LAB occurs at an optimum pH of 4.0 (Mozzi, Oliver, Savoy de Giori, & Font de Valdez, 1995) a pH of 5.5 and temperature of 40 °C were found to be optimal for EPS production by Streptococcus thermophilus 1275 with a very low yield of 458 mg/L (Zisu & Shah, 2003). Similarly, depending on the medium composition , the quantity of EPS produced by S. thermophilus was 152 and 600 mg/L in whey medium (Ricciardi et al., 2002) and skim milk medium (Cerning et al., 1992), respectively . This is very low compared to the yield obtained in the present study. "
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    • "Hydrolysis of EPS fractions and analysis of their composition The HMM-EPS preparations produced by S. thermophilus strains T54 and T6V were found to be different with respect to their monomer composition (Table 1). Glucose was the predominant sugar in the EPS hydrolysates from strain T54 (galactose:glucose : rhamnose ratio of 1:5:1), unlike S. thermophilus strains Sfi12 (Lemoine et al. 1997), SY (Ricciardi et al. 2002), OR 901 (Bubb et al. 1997), and LY03, BTC and Sfi20 (De Vuyst et al. 1998) for which galactose was the prevailing EPS monomer. As other monomer components such as amino-sugars were absent in the hydrolysate from the HMM-EPS of strain T54, this strain falls within group IV of S. thermophilus strains (EPS composed of galactose, glucose and rhamnose) as determined by Vaningelgem et al. (2004). "
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