Properties of yogurts made from whole ewe's milk treated by high hydrostatic pressure

Ewe's milk yogurts were elaborated from high pressure treated (HPP) milk at different combinations of temperature and pressure (10, 25 and 55 °C; 200, 350, 500 MPa for 15 min), from heated milk (HT) (95 °C, 5 min) and from pasteurized milk (control) (70 °C, 10 min). Gel formation, yogurt firmness and syneresis were evaluated. Yogurt firmness increased as pressure increased, but an additional increase in firmness was only observed at 55 °C. The syneresis induced by centrifugation showed a considerable increase in gel water retention when milk combined tretments were 350 and 500 MPa at 25 and 55 °C respectively. Also, in these conditions, the onset of gelation was shorter with higher pH values than those observed in control and HT milk. However, disintegration of CN micelles was only observed when HP was applied at 10 and 25 °C. Yogurt evolution in storage at 4 °C for 20 days showed a good stability in terms of firmness in all treatments but water retention was only mantained in HPP yogurts.