Fermentation profile and characteristics of yoghurt manufactured from frozen sheep milk

Abstract

The impact of yoghurt production from frozen sheep milk was assessed. The milk was thawed one day (T1) or immediately (T0) before processing and the fermentation profile and yoghurt characteristics were compared with those of yoghurt made from fresh (F) milk. With respect to F-yoghurt, the T0-yoghurt acidification rate was 40% slower, acidity (>7.5%) and the shear stress for the yoghurt to start to flow (>16.3%) was higher and its syneresis in set yoghurt (<58.1%) and consistency in set (<21.4%) and stirred (<10.5%) yoghurt were lower. Microstructure indicated the presence of dense protein agglomerates in yoghurts from T0 and T1 milks, but only T0-yoghurt showed lower protein network aggregation. F and T1 yoghurt showed similar characteristics, demonstrating that thawing milk 24 h before production was an alternative to obtain a yoghurt similar to that manufactured from fresh milk. Moreover, sugar addition minimised the differences between yoghurt from F, T0 and T1-milk