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 degrees C; 200, 350, 500 MPa for 15 min), from heated milk (HT) (95 degrees C, 5 mi n) and from pasteurized milk (control) (70 degrees C, 10 min). Gel formatio n, yogurt firmness and syneresis were evaluated. Yogurt firmness increased as pressure increased, but an additional increase in firmness was only obse rved at 55 degrees C. The syneresis induced by centrifugation showed a cons iderable increase in gel water retention when milk combined treatments were 350 and 500 MPa at 25 and 55 degrees C respectively. Also, in these condit ions, the onset of gelation was shorter with higher pH values than those ob served in control and HT milk. However, disintegration of CN micelles was o nly observed when HP was applied at 10 and 25 degrees C. Yogurt evolution i n storage at 4 degrees C for 20 days showed a good stability in terms of fi rmness in all treatments but water retention was only mantained in HPP yogu rts.