Optimizing cryopreservation protocols of Saccharomyces eubayanus using heat transfer modeling

Area of Science:

• Microbiology and Biotechnology
• Biophysics and Engineering

Background:

• Efficient cryopreservation is crucial for industrial yeasts like Saccharomyces eubayanus.
• Understanding heat transfer during freezing is key to optimizing cell viability.

Purpose of the Study:

• To assess the impact of different cryopreservation protocols on S. eubayanus viability.
• To integrate experimental heat transfer data with numerical simulations for cryopreservation analysis.

Main Methods:

• Two freezing protocols were compared: direct freezing in cryoboxes (convection) and freezing in a CoolCell device (conduction).
• Finite element method modeling was used to simulate transient heat transfer during freezing.
• Post-thaw viability and vitality assessments were conducted after one year of storage.

Main Results:

• Direct freezing (Protocol A) achieved optimal cooling rates (5-7°C/min) and higher post-thaw viability (71.7%) compared to the CoolCell device (Protocol B, 51.2%).
• Simulations accurately predicted experimental temperature-time data, allowing estimation of heat transfer coefficients (UA=18.04 W m⁻² K⁻¹, UB=4.76 W m⁻² K⁻¹).
• The overall heat transfer coefficient was identified as a critical parameter for cryopreservation performance.

Conclusions:

• Direct freezing in cryoboxes is a more effective, simpler, and cost-efficient method for cryopreserving S. eubayanus.
• This study provides a basis for standardizing cryogenic storage of yeast for industrial and biotechnological applications.