Production of set yoghurts using thermophilic starters composed of two strains with different growth biocompatibilities and producing different exopolysaccharides

The growth biocompatibility of Streptococcus thermophilus (131, MR1C, HC15) and Lactobacillus delbrueckii subsp. bulgaricus (291, 2074 and 210R) producing free ropy (131 and 291) or capsular non-ropy (MR1C and 2074) exopolysaccharides with different structural characteristics was evaluated using a spectrophotometry technique. Strains with different growth biocompatibilities were combined to produce three thermophilic starters (131/291, MR1C/291, MR1C/2074) used to ferment yoghurt from milk fortified with whey proteins. The syneresis, firmness and viscosity of the yoghurts were monitored for 20 d at 4 °C. Using a starter composed of the incompatible MR1C/2074 strains, the syneresis, firmness and viscosity of the yoghurts were not improved. The highest whey protein content resulted in lower syneresis and higher firmness, viscosity and EPS production in the yoghurts. These effects were more noticeable for starters with free ropy EPS strains, especially with strain 291, which produces stiff β (1 → 4) chains.