Streptococcus thermophilus ST 111 produces a stable high-molecular-mass exopolysaccharide in milk-based medium

Streptococcus thermophilus ST 111, grown in milk medium supplemented with whey protein hydrolysate, produced an exopolysaccharide (EPS) composed of galactose and rhamnose in a molar ratio of 2.5:1, and with a molecular mass of more than 5000 kDa. Fermentations in milk medium supplemented with whey protein hydrolysate further demonstrated the stability of this high-molecular-mass EPS, as its molecular mass was affected neither by the pH of the medium nor the fermentation time, indicating no enzymatic degradation. On the other hand, drying of the isolated EPS resulted in a decrease of the molecular mass. The stability of an EPS produced in milk-based media is an important asset for the production of fermented milk and yoghurt products.