Survival of Lactic acid Bacteria during Microwave Vacuum-drying of Plain Yoghurt

The combined effect of water activity and temperature on the survival of lactic acid bacteria was determined and model regression equations for the survival were developed. The survival of lactic acid bacteria in yoghurt during microwave vacuum-drying was predicted using the developed equations and was compared with experimental valves. Decimal reduction times (D values) of both Streptococcus salivariussubsp. thermophilusand Lactobacillus delbrueckiisubsp. bulgaricusin a mixture (cocci : rod = 1 : 1) had linear (negative) relationships with water activity and temperature in the lower temperature range of 35 to 45 °C; in the higher temperature range of 50 to 60 °C however, the relationships were not linear by exponential. The predicted survival of lactic acid bacteria in yoghurt during microwave vacuum-drying agreed well with the experimental survival.