Production of exopolysaccharides by lactic acid bacteria and dairy propionibacteria

Abstract

Summary -The exopolysaccharide (EPS)-producing gram-positive bacteria which have been studied extensively in the last 10 years are the dairy lactic acid bacteria used in the manufacture of fermented milks such as Streptococcus thermophilus, Lactobacillus delbrueckii subsp bulgaricus and Lactococcus lactis subsp cremoris. The role of exopolysaccharides in the manufacture of fermented milks and in particular yoghurt is weil established; that is, they are essential for proper consistency and texture. A number of strains of these bacteria are capable of producing heteropolysaccharides composed of Iinear or branched repeating units varying in size from disaccharides to heptasaccharides.The final exopolysaccharide of high molecular weight (1 to 2 x 106) is formed by polymerisation of some hundreds to several thousands of these repeating units. Dairy propionibacteria are also capable of producing exopolysaccharides, but this area of research has received comparatively Iittle attention. Nevertheless, similarities appear when the few results obtained with propionibacteria are compared with those concerning dairy lactic acid bacteria. Fermentation conditions (temperature and incubation time) and medium composition (carbon and nitrogen sources) affect the polymer yield and the sugar composition of the polymer. The most frequent identified monosaccharides in polysaccharides formed by propionibacteria are glucose, galactose and mannose. Small amounts of fucose and rhamnose have also been found. A striking difference exists in the molecular weight of polysaccharides produced by lactic acid bacteria and propionibacteria (le, values for exopolysaccharides from the latter are in the range of 200 to 5 000). The polymer-producing ability is an extremely unstable property; it seems to be linked to the presence of plasmids of varying size in mesophilic lactic acid bacteria, whereas most of the exopolysaccharide-producing strains of thermophilic lactic acid bacteria do not harbour plasmids. Propionibacteria harbour plasmids, but their functions are not clearly established; therefore, the question of whether the EPS-producing trait of propionibacteria is plasmid encoded cannot be answered yet.

Exopolysaccharides producing Lactobacillus fermentum strain for enhancing rheological and sensory attributes of low-fat dahi

“…bulgaricus NCDC 285 were glucose: rhamnose : galactose in a proportion of 1 : 13 : 1.5 and rhamnose : galactose in a proportion of 1:6.8 respectively ( Table 1). The monosaccharides most frequently occurring in the various LAB strains are glucose (Cerning 1995), rhamnose (Mozzi et al 2006;Nakajima et al 1990) and galactose (De Vuyst et al 2003;Doleyres et al 2005).…”

Growth and exopolysaccharide production by Streptococcus thermophilus ST1 in skim milk

“…temperature, pH, and components of growth medium and fermentation time, among others (9,27). Streptococcus thermophilus strains have been reported to produce EPSs from 50 to 350 mg l -1 (3). S.…”

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

“…Among the products of their metabolism, extracellular polysaccharides (EPS) have received increasing attention in recent years (Cerning 1995;De Vuyst and Degeest 1999;Ricciardi and Clementi 2000). Lactic acid bacteria usually produce only small amounts of EPS (100-200 mg l -1 ; Cerning 1995) but yields up to 4 g l -1 have been obtained with Lactobacillus sakei O-1 (van den Berg et al 1995).…”