Modeling the inactivation kinetics of lactic acid bacteria in a spray dryer

Changes in the viability of probiotic cells during spray drying were tracked, by developing an inactivation model of Lactobacillus rhamnosus GG (LGG) and coupling the model to the drying kinetics of spray drying using Computational Fluid Dynamics simulation. Six inactivation models in the Arrhenius-equation form were developed using single droplet drying experiments with average drying rates of 0.011–0.044 kg/kg/s; all gave reliable goodness-of-fit. In simulating spray drying process, the predicted moisture content of LGG-containing particles well followed experimental trends. However, only inactivation model 6, which incorporated droplet temperature, moisture content, rate of temperature change, and drying rate, accurately predicted the survival of LGG. Models 1–5 that incorporated fewer kinetics parameters with higher activation energy values underestimated the degree of inactivation. The findings highlighted the crucial effects of the rates of temperature and moisture content change on the inactivation of probiotics during rapid drying with average drying rates of 0.31–0.81 kg/kg/s.