Properties of low-fat stirred yoghurts made from high-pressure-processed skim milk

Physical properties of stirred yoghurt made from reconstituted skim milk that was high-pressure (HP)treated at 100, 250 or 400 MPa, at 25, 70 or 90 degrees C, for 10 min, prior to inoculation with yoghurt cultures, were studied; portions of milk HP-treated at 25 degrees C were also heat-treated at 90 degrees C for 10 min before or after pressure treatment. Control yoghurts were made from skim milk given a heat treatment at 90 degrees C for 10 min. Fermentation time was not affected by treatment applied to the milk. HP treatment of skim milk at 25 degrees C, before or after heat treatment, gave stirred yoghurts of similar viscosities to that made from conventionally heat-treated milk. Lower viscosities were obtained when stirred yoghurts were made with milk HP-treated at elevated temperatures. A model is proposed to correlate properties of yoghurt with HP/heat-induced changes in interactions and structures of protein in the milk samples.