Enzyme Degradation During Spray Drying
Advancing the chemical engineering fundamentals
Particulate Systems (T2-3)
Keywords: Drying Technology, Enzymes, Particle Formation
Jakob Sloth*(1,2), Poul Bach(1), Søren Kiil(2) and Anker D. Jensen(2)
(1) Novozymes A/S , Krogshøjvej 36, DK-2880 Bagsværd, Denmark
(2) Department of Chemical Engineering, Building 229, DK-2800 Lyngby, Denmark
Industrial enzymes are often subject to spray drying because handling is easier and enzyme storage stability is better in a solid product than in a liquid product. However, the enzymes may thermally deactivate during the drying process due to the high temperatures prevailing in the spray dryer. Avoiding this degradation is of primary concern to enzyme producers as any activity loss represents a reduction of the final product value.
In this work a combined experimental and theoretical approach is taken to optimize the spray drying process in terms of minimizing the enzyme degradation. A series of experiments using amylase samples with different water to enzyme ratios have been conducted by differential scanning calorimetry. The experimental data have been used to find reaction rate parameters in a first order reaction model, including an Arrhenius type expression for the rate constant. Also, the reaction order for the water concentration has been identified and the rate of deactivation at different levels of moisture content and temperatures relevant for spray drying may be simulated.
Further, a model for the drying kinetics inside a spray dryer is used to simulate the moisture content and temperature inside a droplet during the course of drying. This model accounts for the most important transport phenomena of the droplet drying process. It includes heat and mass transfer from the bulk to the surface and inside the droplet.
Relevant model parameters have been found experimentally or estimated using thermodynamic correlations. The drying kinetics model has been combined with the model for the amylase deactivation rate. This allows for simulations of the specific deactivation at different process conditions such as bulk air temperature, humidity and initial droplet size to be conducted.
The simulations show that certain combinations of process variables lead to unfortunate temperature and moisture content combinations inside the droplet. This results in significant deactivation which may be lowered by changing the process conditions.
*Corresponding author. jsl@kt.dtu.dk, Phone: +45 45252923, Fax +45 45882258
Presented Monday 17, 15:20 to 15:40, in session Particulate Systems (T2-3).
