Are stirring and homogenisation processes capable of improving physicochemical and sensory characteristics of stirred yoghurt produced with fresh, refrigerated and frozen/thawed sheep milk?

The impacts of stirring and homogenisation processes on the physicochemical and sensory characteristics of stirred yoghurt produced from fresh, refrigerated and frozen/thawed sheep milk were studied. Yoghurt from frozen/thawed milk was more sensitive to post acidification and had a higher Casson yield stress than yoghurt from fresh milk. The main differences caused by stirring and homogenisation were observed in NIR backscattering and in rheological parameters of yoghurt from refrigerated and frozen/thawed milk (Casson yield stress reduced and Casson consistency index increased). These modifications, however, were not able to improve the low scores of sensory evaluation of yoghurt from frozen/thawed milk, probably penalised by their worst textures. Results suggest that sheep milk cold preservation, mainly freezing/thawing, negatively affects the characteristics of yoghurt; although some improvements in physicochemical parameters are observed after stirring and homogenisation, these were not enough to avoid poor sensory evaluation of the samples.