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

摘要

Effects of 2 Streptococcus thermophilus strains, ST 285 and ST 1275, on selected technological and rheological characteristics of set-type yoghurt were determined. Strains were selected for their ability to produce distinctly different exopolysaccharides (EPS) and were coded as capsular (ST 285) or ropy-capsular (ST 1275). Culture performance and physicochemical properties of the yoghurt were assessed in relation to different fermentation temp. (30, 37 or 42 degrees C) and prolonged storage (up to 30 days) at low temp. (4 degrees C). ST 1275 showed faster growth and acidification rates, resulting in yoghurt with lower syneresis and a higher flow behaviour index than ST 285. EPS production appeared to be growth associated with the max. at a growth temp. of 37 and 42 degrees C for ST 285 and ST 1275, respectively; however, EPS concn. decreased 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 concn. and yoghurt texture was observed.