Effect of exopolysaccharide-producing starter cultures and post-fermentation mechanical treatment on textural properties and microstructure of low fat yoghurt

The microstructure and texture of yoghurts produced by four different exopolysaccharide (EPS)-producing starter cultures and mechanically treated post-fermentation at four levels of intensity (applied back-pressure) were studied. Two Lactobacillus delbrueckii ssp. bulgaricus (LB) strains were used in combination with two Streptococcus thermophilus (ST) strains and yoghurts were formulated by pairwise combining one LB and one ST strain. The choice of ST strain was the major determinant for the rheological properties of the yoghurts, since one of the ST strains conferred a ropy texture and resulted in yoghurts with decreased water holding capacity and an open microstructure. In addition, one of the LB strains used produced both aggregated and threadlike EPS and improved water holding. When combined with an ST strain that produced neglible amounts of EPS this LB strain resulted in yoghurt where a moderate mechanical treatment post-fermentation was able to further improve the water holding capacity.