DEATH KINETICS OF LACTOBACILLUS-BULGARICUS IN A SPRAY-DRYING PROCESS

Survival of Lactobacillus bulgaricus during spray drying was studied a t various outlet air temperatures. During spray drying the logarithmic survival ratio decreased with increased outlet air temperature with f irst-order kinetics; the pseudo-z value for Lactobacillus bulgaricus w as 17.3 degrees C. Plots of the death-rate constant for Lactobacillus bulgaricus versus reciprocal outlet temperature during spray drying in skim milk show a curve with two different activation energies (E(a)). The calculated E(a) values were 33.47 kJ/mol above 70 degrees C and 8 5.77 kJ/mol below 70 degrees C. Thermodynamic quantities for spray dry ing of Lactobacillus bulgaricus are also presented. Results show that the relationship between the entropy of activation and the enthalpy of activation for both spray drying and heating in liquid medium is line ar, with all the data for drying falling in the range of a negative en tropy.