Effect of spray drying temperature of yoghurt on the survival of starter cultures, moisture content and sensoric properties of yoghurt powder

A synergistic set of the strains Lactobacillus delbrueckii subsp. bulgaricus 151 and Streptococcus thermophilus MK-10 was preserved with the method of spray drying. Studies were performed on the effect of outlet air temperature in range of 60-80 degrees C upon the survival of yoghurt cultures, as well as the moisture content and sensoric properties of yoghurt powder. Survival of yoghurt cultures was the highest at 60 and 65 degrees C, but excessive moisture (10.2%) of yoghurt powder had a negative effect on its texture. Moisture content of the powder was low at 80 degrees C (4.4%), unfortunately sensoric faults appeared at this temperature, and survival of bacteria cultures decreased considerably. Temperatures within the range 70-75 degrees C ensured satisfactory survival of yoghurt cultures (L. delbrueckii subsp. bulgaricus - 13.7-15.8%; S. thermophilus - 51.6-54.7%), maintained proportion of the strains (L:S-1:3), satisfactory moisture content (5.1-6.3%), and good sensoric properties of yoghurt powder.