Effects of exopolysaccharide-producing strains of Streptococcus thermophilus on technological and rheological properties of set-type yoghurt

This study investigated the effects of two Streptococcus thermophilus strains, ST 285 and ST 1275, on selected technological and rheoloaical characteristics of set-type yoghurt. The strains were selected for their capability to produce distinctly different exopolysaccharides (EPS) and were thus coded as capsular (ST 285) or ropy-capsular (ST 1275). The culture performance and physico-chemical properties of yoghurt were assessed in relation to different fermentation temperatures (30, 37 or 42 degrees C) and prolonged storage (up to 30 days) at low temperature (4 degrees C). ST 1275 showed faster growth and acidification rates, resulting in yoghurt with lower syneresis and higher-flow behaviour index, than ST 285. EPS production appeared to be growth associated with the maximum given at growth temperatures of 37 and 42 degrees C for ST 285 and ST 1275, respectively; however, EPS concentration declined considerably during storage. Prolonged cold storage increased several rheological characteristics of yoghurt including G', consistency index and hysteresis loop area. A weak correlation between EPS concentration and textural properties of yoghurt was observed. (c) 2007 Elsevier Ltd. All rights reserved.