RELATION BETWEEN SENSORY TEXTURE PROPERTIES AND EXOPOLYSACCHARIDE DISTRIBUTION IN SET AND IN STIRRED YOGHURTS PRODUCED WITH DIFFERENT STARTER CULTURES

摘要

Set yoghurts produced with seven different exopolysaccharide-producing starter cultures were subjected to sensory texture profiling including texture evaluation before and after a stirring procedure carried out by trained assessors. The microstructure of four selected yoghurts was investigated by con-focal laser scanning microscopy with special focus on the distribution of exopolysaccharides (EPS) in the protein network. Two different types of micro-structures were observed, one in which EPS were associated with the protein network and another where EPS appeared to be incompatible with the protein; as a consequence, the EPS were situated in the void spaces in the protein network. The latter yoghurts were less ropy and had higher serum separation than the yoghurts where EPS were associated with the protein, and they exhibited a significant increase in mouth thickness as a result of stirring. Yoghurts in which the EPS were associated with protein had high ropiness, low serum separation and appeared more resistant to stirring. The nature of EPS-protein interactions is extremely important for the textural effects of EPS in fermented milk products, and such interactions depend on the specific starter culture used.