Investigation of Physicochemical, Microbiological, and Rheological Properties and Volatile Compounds of Ewe and Cow Milk Yoghurt

Yoghurt, with viscous texture and containing volatile compounds, has special appeal for the consumer. In this study, to produce such a yoghurt without any additives, two types of yoghurt from ewe and cow milk were prepared. The samples were evaluated for physicochemical and volatile compounds and viscosity on the first, 7th, and 14th days of shelf life. In addition, the enumeration and viability of Lb. bulgaricus and Str. thermophilus were studied. Ewe yoghurt had more dry matter, protein, and acid production ability compared to cow yoghurt, with lower pH. The number of lactobacilli was greater in ewe yoghurt which caused increase in acidity and decrease in pH value in ewe yoghurt. The number of lactobacilli and streptococcus decreased during shelf life of both yoghurts. The viscosity of ewe yoghurt was greater than cow yoghurt and it increased during 14 days of storage. Regarding volatile compounds, acetaldehyde and diacetyl decreased during shelf life while ethanol increased in both cow and ewe milk yoghurt.