Death Kinetics of Lactobacillus bulgaricus in a Spray Drying Process.

Area of Science:

• Food Microbiology
• Biotechnology
• Chemical Engineering

Background:

• Lactobacillus bulgaricus is a key probiotic microorganism.
• Spray drying is a common method for preserving probiotics, but survival rates can be affected by process parameters.
• Understanding the kinetics and thermodynamics of spray drying is essential for maintaining probiotic viability.

Purpose of the Study:

• To investigate the survival of Lactobacillus bulgaricus during spray drying under varying outlet air temperatures.
• To determine the kinetic parameters, including the pseudo-z value and death-rate constants.
• To analyze the thermodynamic aspects of Lactobacillus bulgaricus survival during spray drying.

Main Methods:

• Spray drying of Lactobacillus bulgaricus in skim milk at different outlet air temperatures.
• Measurement of logarithmic survival ratios and calculation of death-rate constants.
• Determination of activation energies (Ea) and thermodynamic quantities (entropy and enthalpy of activation).

Main Results:

• Logarithmic survival ratio decreased with increasing outlet air temperature, following first-order kinetics.
• The pseudo-z value for Lactobacillus bulgaricus was determined to be 17.3°C.
• Two distinct activation energies were calculated: 33.47 kJ/mol above 70°C and 85.77 kJ/mol below 70°C. A linear relationship was observed between entropy and enthalpy of activation, with negative entropy for drying.

Conclusions:

• Outlet air temperature is a critical factor influencing Lactobacillus bulgaricus survival during spray drying.
• The study provides specific kinetic and thermodynamic data that can be used to optimize spray drying conditions for enhanced probiotic survival.
• The findings contribute to a better understanding of the physical and chemical stresses experienced by probiotics during spray drying.